diff --git a/game/internal/controller/ship_group_upgrade.go b/game/internal/controller/ship_group_upgrade.go
index 3dda566..0ec3593 100644
--- a/game/internal/controller/ship_group_upgrade.go
+++ b/game/internal/controller/ship_group_upgrade.go
@@ -5,6 +5,7 @@ import (
 	"slices"
 	"strings"
 
+	"galaxy/calc"
 	e "galaxy/error"
 
 	"galaxy/game/internal/model/game"
@@ -156,26 +157,19 @@ func (uc UpgradeCalc) UpgradeMaxShips(resources float64) uint {
 	return uint(math.Floor(resources / uc.UpgradeCost(1)))
 }
 
-func BlockUpgradeCost(blockMass, currentBlockTech, targetBlockTech float64) float64 {
-	if blockMass == 0 || targetBlockTech <= currentBlockTech {
-		return 0
-	}
-	return (1 - currentBlockTech/targetBlockTech) * 10 * blockMass
-}
-
 func GroupUpgradeCost(sg *game.ShipGroup, st game.ShipType, drive, weapons, shields, cargo float64) UpgradeCalc {
 	uc := &UpgradeCalc{Cost: make(map[game.Tech]float64)}
 	if drive > 0 {
-		uc.Cost[game.TechDrive] = BlockUpgradeCost(st.DriveBlockMass(), sg.TechLevel(game.TechDrive).F(), drive)
+		uc.Cost[game.TechDrive] = calc.BlockUpgradeCost(st.DriveBlockMass(), sg.TechLevel(game.TechDrive).F(), drive)
 	}
 	if weapons > 0 {
-		uc.Cost[game.TechWeapons] = BlockUpgradeCost(st.WeaponsBlockMass(), sg.TechLevel(game.TechWeapons).F(), weapons)
+		uc.Cost[game.TechWeapons] = calc.BlockUpgradeCost(st.WeaponsBlockMass(), sg.TechLevel(game.TechWeapons).F(), weapons)
 	}
 	if shields > 0 {
-		uc.Cost[game.TechShields] = BlockUpgradeCost(st.ShieldsBlockMass(), sg.TechLevel(game.TechShields).F(), shields)
+		uc.Cost[game.TechShields] = calc.BlockUpgradeCost(st.ShieldsBlockMass(), sg.TechLevel(game.TechShields).F(), shields)
 	}
 	if cargo > 0 {
-		uc.Cost[game.TechCargo] = BlockUpgradeCost(st.CargoBlockMass(), sg.TechLevel(game.TechCargo).F(), cargo)
+		uc.Cost[game.TechCargo] = calc.BlockUpgradeCost(st.CargoBlockMass(), sg.TechLevel(game.TechCargo).F(), cargo)
 	}
 	return *uc
 }
@@ -218,7 +212,7 @@ func UpgradeGroupPreference(sg game.ShipGroup, st game.ShipType, tech game.Tech,
 		ti = len(su.UpgradeTech) - 1
 	}
 	su.UpgradeTech[ti].Level = game.F(v)
-	su.UpgradeTech[ti].Cost = game.F(BlockUpgradeCost(st.BlockMass(tech), sg.TechLevel(tech).F(), v) * float64(sg.Number))
+	su.UpgradeTech[ti].Cost = game.F(calc.BlockUpgradeCost(st.BlockMass(tech), sg.TechLevel(tech).F(), v) * float64(sg.Number))
 
 	sg.StateUpgrade = &su
 	return sg
diff --git a/game/internal/controller/ship_group_upgrade_test.go b/game/internal/controller/ship_group_upgrade_test.go
index 393abdf..df885fc 100644
--- a/game/internal/controller/ship_group_upgrade_test.go
+++ b/game/internal/controller/ship_group_upgrade_test.go
@@ -13,12 +13,6 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestBlockUpgradeCost(t *testing.T) {
-	assert.Equal(t, 00.0, controller.BlockUpgradeCost(1, 1.0, 1.0))
-	assert.Equal(t, 25.0, controller.BlockUpgradeCost(5, 1.0, 2.0))
-	assert.Equal(t, 50.0, controller.BlockUpgradeCost(10, 1.0, 2.0))
-}
-
 func TestGroupUpgradeCost(t *testing.T) {
 	sg := &g.ShipGroup{
 		Tech: map[g.Tech]g.Float{
diff --git a/pkg/calc/ship.go b/pkg/calc/ship.go
index 0b96271..b0919f3 100644
--- a/pkg/calc/ship.go
+++ b/pkg/calc/ship.go
@@ -52,6 +52,17 @@ func WeaponsBlockMass(weapons float64, armament uint) (float64, bool) {
 	return float64(armament+1) * (weapons / 2), true
 }
 
+// Стоимость модернизации одного блока корабля -
+// доля недостающего технологического уровня (1 - currentBlockTech/targetBlockTech),
+// умноженная на массу блока и нормирующий коэффициент 10.
+// Возвращает 0, если масса блока равна нулю или целевой уровень не выше текущего.
+func BlockUpgradeCost(blockMass, currentBlockTech, targetBlockTech float64) float64 {
+	if blockMass == 0 || targetBlockTech <= currentBlockTech {
+		return 0
+	}
+	return (1 - currentBlockTech/targetBlockTech) * 10 * blockMass
+}
+
 func DestructionProbability(
 	attackingWeapons,
 	attackingWeaponsTech,
diff --git a/pkg/calc/ship_test.go b/pkg/calc/ship_test.go
new file mode 100644
index 0000000..09b0ba1
--- /dev/null
+++ b/pkg/calc/ship_test.go
@@ -0,0 +1,34 @@
+package calc_test
+
+import (
+	"math"
+	"testing"
+
+	"galaxy/calc"
+)
+
+func TestBlockUpgradeCost(t *testing.T) {
+	cases := []struct {
+		name        string
+		blockMass   float64
+		currentTech float64
+		targetTech  float64
+		want        float64
+	}{
+		{"zero block mass returns zero", 0, 1.0, 2.0, 0},
+		{"target equal to current returns zero", 5, 2.0, 2.0, 0},
+		{"target below current returns zero", 5, 2.0, 1.0, 0},
+		{"doubling tech on mass 5 costs 25", 5, 1.0, 2.0, 25},
+		{"doubling tech on mass 10 costs 50", 10, 1.0, 2.0, 50},
+		{"partial step from 2.0 to 2.5 on mass 5", 5, 2.0, 2.5, 10},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := calc.BlockUpgradeCost(tc.blockMass, tc.currentTech, tc.targetTech)
+			if math.Abs(got-tc.want) > 1e-9 {
+				t.Errorf("BlockUpgradeCost(%v, %v, %v) = %v, want %v",
+					tc.blockMass, tc.currentTech, tc.targetTech, got, tc.want)
+			}
+		})
+	}
+}
diff --git a/ui/PLAN.md b/ui/PLAN.md
index 295578d..7fe2776 100644
--- a/ui/PLAN.md
+++ b/ui/PLAN.md
@@ -2135,27 +2135,63 @@ Targeted tests:
 - Playwright e2e: click each variant from a seeded game, assert all
   expected fields render.
 
-## Phase 20. Inspector — Ship Group Actions
+## ~~Phase 20. Inspector — Ship Group Actions~~
 
-Status: pending.
+Status: done.
 
 Goal: enable group operations from the inspector: split, send, load,
 unload, modernize, dismantle, transfer to race, add to fleet.
 
 Artifacts:
 
-- action buttons in `ui/frontend/src/lib/inspectors/ship-group.svelte`
-  with disabled-state and tooltip when local validation rejects
-- `ui/frontend/src/sync/order-types.ts` extends with `SplitGroup`,
-  `SendGroup`, `LoadCargo`, `UnloadCargo`, `Modernize`, `Dismantle`,
-  `TransferToRace`, `AssignToFleet` command variants
-- `Send` action picks destination through a planet picker filtered by
-  the group's reach (uses `pkg/calc/` reach function via Core; the
-  player's tech levels are already on `GameReport.localPlayer*` from
-  Phase 18, no extra plumbing needed)
-- `Modernize` cost preview using `pkg/calc/` formula via Core
-- confirmation dialog for `Dismantle` over a foreign planet with
-  colonists onboard (special-case from [`rules.txt`](../game/rules.txt): colonists die)
+- action panel `ui/frontend/src/lib/inspectors/ship-group/actions.svelte`
+  mounted by the read-only inspector for the local variant; eight
+  inline forms (one per action) with disabled-button tooltips that
+  mirror the engine's pre-conditions
+  (`controller/ship_group*.go`)
+- `ui/frontend/src/sync/order-types.ts` extends with eight new
+  command variants — `breakShipGroup`, `sendShipGroup`,
+  `loadShipGroup`, `unloadShipGroup`, `upgradeShipGroup`,
+  `dismantleShipGroup`, `transferShipGroup`, `joinFleetShipGroup` —
+  plus `ShipGroupCargo` and `ShipGroupUpgradeTech` literal types
+- `sync/submit.ts` and `sync/order-load.ts` round-trip every new
+  variant against the existing FBS classes in
+  `proto/galaxy/fbs/order/`; the `id` field on each ship-group
+  payload carries the *target* group UUID (the source group, or
+  the freshly-minted `newGroupId` when an implicit split precedes
+  the action)
+- `Send` action picks destination through a planet picker filtered
+  by the group's reach (`localPlayerDrive * 40`, computed inline
+  via the existing `torusShortestDelta` from
+  `cargo-routes.svelte`); the player's tech levels are already on
+  `GameReport.localPlayer*` from Phase 18, no extra plumbing
+  needed
+- `Modernize` cost preview through `core.blockUpgradeCost`
+  (Phase 20 bridge), summed over the four ship-class blocks for
+  the targeted ship count; preview hides when `Core` is not yet
+  booted or the form is invalid (see
+  `ui/docs/ship-group-actions.md` for the formula breakdown)
+- two-step inline confirmation for `Dismantle` over a foreign
+  planet with colonists onboard (engine reference
+  `controller/ship_group.go:177-179` — `UnloadColonists` is not
+  called over a foreign planet, so the cargo is lost)
+- `pkg/calc/ship.go.BlockUpgradeCost` (migrated from
+  `game/internal/controller/ship_group_upgrade.go`) — the bridge
+  rule says `ui/core/calc/` only wraps `pkg/calc/` formulas, so
+  the function moved upstream and the controller now imports it
+- `GameReport.otherRaces: string[]` populated by the report
+  decoder from `report.player[]` (non-extinct, ≠ self) — used by
+  the transfer-to-race picker; Phase 22's Races View reuses the
+  same field
+- planet inspector's stationed-ship rows
+  (`lib/inspectors/planet/ship-groups.svelte`) become clickable
+  for own groups, pivoting the `SelectionStore` to the matching
+  `shipGroup.local` ref so the actions panel is reachable from
+  the standard click flow (the map deliberately hides on-planet
+  groups, so this is the on-planet entry point)
+- topic doc `ui/docs/ship-group-actions.md` covers the action
+  surface, disabled-state rules, implicit-split pattern, and the
+  modernize cost preview formula
 
 Dependencies: Phases 18, 19.
 
@@ -2171,10 +2207,61 @@ Acceptance criteria:
 
 Targeted tests:
 
-- Vitest unit tests for action enablement logic per action;
-- Vitest component tests for the dismantle-with-colonists confirmation;
-- Playwright e2e for at least one complete flow (send a group between
-  two planets) against a local stack.
+- `pkg/calc/ship_test.go.TestBlockUpgradeCost` — formula coverage
+  on the migrated function;
+- `ui/core/calc/ship_test.go.TestBlockUpgradeCostParity` — bridge
+  parity against `pkg/calc/`;
+- Vitest:
+  - `tests/inspector-ship-group-actions.test.ts` — disabled-state
+    rules per action and the implicit-split pattern;
+  - `tests/inspector-ship-group-dismantle-confirm.test.ts` —
+    two-step confirm over foreign-COL groups;
+  - `tests/inspector-ship-group-modernize-cost.test.ts` —
+    preview formula matches `BlockUpgradeCost` × ship count and
+    hides when `Core` is null;
+  - `tests/sync-order-types-ship-group.test.ts` —
+    `validateCommand` for each new variant;
+  - `tests/sync-submit-ship-group.test.ts` — encoder/decoder
+    round-trip per new variant;
+- Playwright `tests/e2e/ship-group-send.spec.ts` — synthetic
+  report with a 3-ship group on Earth and a reachable Mars,
+  drives the planet inspector → ship-group inspector pivot, then
+  Send 2 of 3 with map-pick destination, asserts both Break and
+  Send land in the order draft via the order tab.
+
+Decisions during stage:
+
+1. **`BlockUpgradeCost` migration**. The pre-existing copy in
+   `game/internal/controller/ship_group_upgrade.go` moved to
+   `pkg/calc/ship.go`; the controller's `GroupUpgradeCost` and
+   `UpgradeGroupPreference` now call `calc.BlockUpgradeCost`.
+   The unit test moved from `controller/ship_group_upgrade_test.go`
+   to `pkg/calc/ship_test.go`.
+2. **`GameReport.otherRaces`** field added to
+   `ui/frontend/src/api/game-state.ts`; the synthetic-report
+   decoder populates it the same way (`api/synthetic-report.ts`).
+   Phase 22's Races View can read this directly without a fresh
+   plumbing pass — the Phase 22 stage text below is updated to
+   reflect that.
+3. **Stationed-ship rows are clickable**. The Phase 19 stationed-
+   ship subsection on the planet inspector becomes interactive
+   for own groups (Phase 21+ table view stays a separate target).
+   The map renderer continues to hide on-planet groups — this is
+   the cheaper navigational fix.
+4. **Inline forms, no modal**. Every action opens an inline
+   editor under the buttons row, matching the Phase 14 rename and
+   Phase 16 cargo-route patterns. Send reuses
+   `MAP_PICK_CONTEXT_KEY` (Phase 16's renderer service) for the
+   destination picker. Foreign-COL Dismantle uses a two-step
+   inline confirm (button label flips to "confirm — colonists
+   die") rather than a separate modal component.
+5. **Implicit split for Send/Load/Unload/Modernize/Dismantle/
+   Transfer**. The number-of-ships input defaults to the group's
+   full count; when the player picks a smaller M, the inspector
+   prepends `breakShipGroup(id, newId, M)` and routes the action
+   at `newId`. JoinFleet and Split do not get a counter (JoinFleet
+   is whole-group atomically per the engine; Split *is* the break
+   command).
 
 ## Phase 21. Sciences — CRUD List + Designer
 
@@ -2226,7 +2313,12 @@ Artifacts:
 - `ui/frontend/src/routes/games/[id]/table/races/+page.svelte` table
   with one row per race, including name, tech levels, total
   population, total production, planet count, war-or-peace from this
-  race's perspective, votes received
+  race's perspective, votes received. The race list itself is read
+  from `GameReport.otherRaces` (introduced in Phase 20 for the
+  ship-group transfer-to-race picker); the table view widens the
+  per-race shape (tech / population / production / planet count /
+  votes / relation) by walking `report.player[]` directly when those
+  fields are needed
 - per-row toggle for declaring war or peace (adds
   `SetDiplomaticStance` command)
 - voting control: a single slot for `give my votes to <race>` (adds
diff --git a/ui/core/calc/ship.go b/ui/core/calc/ship.go
index d1bf5e8..1a446c9 100644
--- a/ui/core/calc/ship.go
+++ b/ui/core/calc/ship.go
@@ -55,3 +55,13 @@ func CargoCapacity(cargo, cargoTech float64) float64 {
 func CarryingMass(load, cargoTech float64) float64 {
 	return calc.CarryingMass(load, cargoTech)
 }
+
+// BlockUpgradeCost wraps `calc.BlockUpgradeCost` (`pkg/calc/ship.go`):
+// production cost of upgrading a single ship block from currentBlockTech
+// to targetBlockTech. Returns 0 when blockMass is zero or the target is
+// not above the current level. Used by the ship-group inspector's
+// modernize cost preview, with each of the four blocks (drive, weapons,
+// shields, cargo) priced through a separate call.
+func BlockUpgradeCost(blockMass, currentBlockTech, targetBlockTech float64) float64 {
+	return calc.BlockUpgradeCost(blockMass, currentBlockTech, targetBlockTech)
+}
diff --git a/ui/core/calc/ship_test.go b/ui/core/calc/ship_test.go
index de6f3c1..529802f 100644
--- a/ui/core/calc/ship_test.go
+++ b/ui/core/calc/ship_test.go
@@ -171,6 +171,31 @@ func TestCarryingMassParity(t *testing.T) {
 	}
 }
 
+func TestBlockUpgradeCostParity(t *testing.T) {
+	t.Parallel()
+	cases := []struct {
+		name        string
+		blockMass   float64
+		currentTech float64
+		targetTech  float64
+	}{
+		{"zero_block_mass", 0, 1, 2},
+		{"target_equal_to_current", 5, 2, 2},
+		{"target_below_current", 5, 2, 1},
+		{"doubling_tech_on_mass_5", 5, 1, 2},
+		{"partial_step_2_to_2_5", 5, 2, 2.5},
+		{"high_tech_to_higher_tech", 12, 4, 6},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			t.Parallel()
+			want := source.BlockUpgradeCost(c.blockMass, c.currentTech, c.targetTech)
+			got := bridge.BlockUpgradeCost(c.blockMass, c.currentTech, c.targetTech)
+			assert.Equal(t, want, got)
+		})
+	}
+}
+
 // TestDesignerPreviewComposition exercises the exact composition the
 // ship-class designer performs: empty mass, full-load mass via
 // CarryingMass(CargoCapacity), max speed at empty, and range at full
diff --git a/ui/docs/calc-bridge.md b/ui/docs/calc-bridge.md
index 15446a2..6d88ebb 100644
--- a/ui/docs/calc-bridge.md
+++ b/ui/docs/calc-bridge.md
@@ -9,30 +9,33 @@ Go → WASM → TypeScript bridge mounted under `ui/core/calc/` and a
 matching TS adapter in `ui/frontend/src/platform/core/`.
 
 Phase 18 lands the **ship-math slice** of the bridge — everything
-the ship-class designer needs to render its preview pane. Other
-slices (production forecast, science research, ship build progress)
-remain deferred to dedicated future phases. This document is the
-running audit trail of what is live, what is missing, and how each
-function maps to its `pkg/calc/` source.
+the ship-class designer needs to render its preview pane. Phase 20
+extends it with `BlockUpgradeCost` so the ship-group inspector can
+preview modernize cost. Other slices (production forecast, science
+research, ship build progress) remain deferred to dedicated future
+phases. This document is the running audit trail of what is live,
+what is missing, and how each function maps to its `pkg/calc/`
+source.
 
-## Live bridge surface (Phase 18)
+## Live bridge surface
 
 The Go module `galaxy/core/calc` (`ui/core/calc/ship.go`) exposes
-seven thin wrappers around `pkg/calc/ship.go`. Each is a one-line
-passthrough — the bridge contains zero math. The same seven names
-appear on the JS-side `globalThis.galaxyCore` (registered in
+thin wrappers around `pkg/calc/ship.go`. Each is a one-line
+passthrough — the bridge contains zero math. The same names appear
+on the JS-side `globalThis.galaxyCore` (registered in
 `ui/wasm/main.go`) and on the typed `Core` interface
 (`ui/frontend/src/platform/core/index.ts`).
 
-| Bridge function    | `pkg/calc/` source                                  | JS return shape | Used by                          |
-| ------------------ | --------------------------------------------------- | --------------- | -------------------------------- |
-| `driveEffective`   | `calc.DriveEffective(drive, driveTech)`             | `number`        | designer preview (`Speed` input) |
-| `emptyMass`        | `calc.EmptyMass(drive, weapons, armament, …)`       | `number\|null`  | designer preview (mass row)      |
-| `weaponsBlockMass` | `calc.WeaponsBlockMass(weapons, armament)`          | `number\|null`  | reserved for future stages       |
-| `fullMass`         | `calc.FullMass(emptyMass, carryingMass)`            | `number`        | designer preview (full-load row) |
-| `speed`            | `calc.Speed(driveEffective, fullMass)`              | `number`        | designer preview (speed + range) |
-| `cargoCapacity`    | `calc.CargoCapacity(cargo, cargoTech)`              | `number`        | designer preview (cargo row)     |
-| `carryingMass`     | `calc.CarryingMass(load, cargoTech)`                | `number`        | designer preview (full-load mass)|
+| Bridge function     | `pkg/calc/` source                                       | JS return shape | Used by                                  |
+| ------------------- | -------------------------------------------------------- | --------------- | ---------------------------------------- |
+| `driveEffective`    | `calc.DriveEffective(drive, driveTech)`                  | `number`        | designer preview (`Speed` input)         |
+| `emptyMass`         | `calc.EmptyMass(drive, weapons, armament, …)`            | `number\|null`  | designer preview (mass row)              |
+| `weaponsBlockMass`  | `calc.WeaponsBlockMass(weapons, armament)`               | `number\|null`  | designer preview, modernize cost preview |
+| `fullMass`          | `calc.FullMass(emptyMass, carryingMass)`                 | `number`        | designer preview (full-load row)         |
+| `speed`             | `calc.Speed(driveEffective, fullMass)`                   | `number`        | designer preview (speed + range)         |
+| `cargoCapacity`     | `calc.CargoCapacity(cargo, cargoTech)`                   | `number`        | designer preview (cargo row)             |
+| `carryingMass`      | `calc.CarryingMass(load, cargoTech)`                     | `number`        | designer preview (full-load mass)        |
+| `blockUpgradeCost`  | `calc.BlockUpgradeCost(blockMass, currentTech, target)`  | `number`        | ship-group inspector modernize preview   |
 
 `number|null` returns mirror the Go `(float64, bool)` signature: the
 upstream validator rejects weapons/armament pairings with one zero
@@ -64,6 +67,8 @@ waivers below for the rationale on each deferral.
 | `ShipProductionCost(shipEmptyMass float64) float64`    | Production units required per unit of ship empty mass (×10).                                     |
 | `PlanetProduceShipMass(L, Mat, Res float64) float64`   | Ship mass produced per turn given free production `L`, material stockpile `Mat`, resources `Res`.|
 | `DriveEffective`, `Speed`, `EmptyMass`, `FullMass`, …  | Ship-level derivations (`pkg/calc/ship.go`).                                                     |
+| `BlockUpgradeCost(blockMass, currentTech, target)`     | Production cost of upgrading a single ship block (Phase 20 migrated this from `controller`).     |
+| `FligthDistance(driveTech)`, `VisibilityDistance(...)` | Race-level reach formulas (`pkg/calc/race.go`).                                                  |
 | `ValidateShipTypeValues`, `CheckShipTypeValueDWSC`     | Ship-design validators (`pkg/calc/validator.go`).                                                |
 
 Nothing else lives in `pkg/calc/` today. Production-side formulas
@@ -79,6 +84,7 @@ whether the underlying Go function exists.
 | UI feature                                        | Go formula                                                                                                                  | In `pkg/calc/`? | Surfaced to TS? |
 | ------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------- | :-------------: | :-------------: |
 | Ship-class designer preview (Phase 18)            | `EmptyMass`, `FullMass`, `Speed`, `DriveEffective`, `CargoCapacity`, `CarryingMass`, `WeaponsBlockMass` (`pkg/calc/ship.go`) |       yes       |       yes       |
+| Ship-group modernize cost preview (Phase 20)      | `BlockUpgradeCost` (`pkg/calc/ship.go`, migrated from `game/internal/controller/ship_group_upgrade.go`)                     |       yes       |       yes       |
 | Free production potential (`freeIndustry`)        | `Planet.ProductionCapacity` → `industry*0.75 + population*0.25` (`game/internal/model/game/planet.go`)                       |       no        |       no        |
 | Industry production output per turn               | `Planet.ProduceIndustry(freeProduction)` (`planet.go`); `freeProduction/5` modulo material constraint                       |       no        |       no        |
 | Materials production output per turn              | `Planet.ProduceMaterial(freeProduction)` (`planet.go`); `freeProduction * resources`                                          |       no        |       no        |
diff --git a/ui/docs/ship-group-actions.md b/ui/docs/ship-group-actions.md
new file mode 100644
index 0000000..eb5cf98
--- /dev/null
+++ b/ui/docs/ship-group-actions.md
@@ -0,0 +1,151 @@
+# Ship-group inspector actions
+
+Phase 20 turns the read-only ship-group inspector
+(`ui/frontend/src/lib/inspectors/ship-group.svelte`) into an
+interactive command source for the player's own groups in orbit.
+This document is the running spec for the actions panel
+(`ui/frontend/src/lib/inspectors/ship-group/actions.svelte`):
+which actions exist, what gates each one, how partial-ship
+operations split a group on the fly, and what the modernize cost
+preview shows.
+
+## Reaching a group
+
+The map renderer hides on-planet ship groups to avoid crowding
+the canvas. The player reaches an own on-planet group through the
+planet inspector's **stationed ship groups** subsection: clicking
+a row pivots the `SelectionStore` to the matching
+`shipGroup.local` ref, the sidebar swaps from the planet
+inspector to the ship-group inspector, and the actions panel
+mounts. In-flight (in-space) groups appear as map primitives and
+can be selected by clicking the rendered point.
+
+## Action surface
+
+| Action      | Implicit-split? | Partial input | FBS payload                  | Engine reference                                      |
+| ----------- | :-------------: | ------------- | ---------------------------- | ----------------------------------------------------- |
+| Split       |       —         | ships count   | `CommandShipGroupBreak`      | `controller/ship_group.go.breakGroup`                  |
+| Send        |       yes       | ships count + destination | `CommandShipGroupSend` | `controller/ship_group_send.go.shipGroupSend`         |
+| Load        |       yes       | ships count + cargo + quantity | `CommandShipGroupLoad` | `controller/ship_group.go.shipGroupLoad`              |
+| Unload      |       yes       | ships count + quantity | `CommandShipGroupUnload` | `controller/ship_group.go.shipGroupUnload`            |
+| Modernize   |       yes       | ships count + tech + level | `CommandShipGroupUpgrade` | `controller/ship_group_upgrade.go.shipGroupUpgrade` |
+| Dismantle   |       yes       | ships count + foreign-COL confirm | `CommandShipGroupDismantle` | `controller/ship_group.go.shipGroupDismantle`         |
+| Transfer    |       yes       | ships count + acceptor race | `CommandShipGroupTransfer` | `controller/ship_group.go.shipGroupTransfer`          |
+| Join Fleet  |       —         | fleet name (existing or new) | `CommandShipGroupJoinFleet` | `controller/fleet.go.ShipGroupJoinFleet`              |
+
+"Implicit-split" means the inspector accepts a number of ships
+`M < N` and emits a `CommandShipGroupBreak(id, newId, M)` command
+*before* the action command, then targets the action at the
+freshly-minted `newId`. The FBS schema only carries a per-ship
+`quantity` on `CommandShipGroupBreak`; every other ship-group
+command applies to the whole group, so the implicit-split
+pattern is the only way to act on a subset without forcing the
+player to pre-split manually. Acceptance criteria: "splitting a
+group of N into K and N-K results in two valid commands" — that
+is exactly the (Break, Action) pair this pipeline emits.
+
+Split and Join Fleet do not accept a partial ship count: Split
+*is* the break operation; Join Fleet attaches the whole group
+atomically (the engine handles a partial detach by issuing Split
+first, which the player drives explicitly).
+
+## Disabled-state rules
+
+The inspector mirrors the engine's pre-conditions per command
+(see the references column above) and surfaces each as a
+disabled-button tooltip. Any state other than `In_Orbit` disables
+every action with `ships are busy ({state})`. Per-action gates:
+
+- **Send**: requires the ship class to have a non-zero drive
+  block (`controller/ship_group_send.go:32`); the picker
+  pre-filters destinations by reach
+  (`localPlayerDrive * 40`), so a valid pick is always within
+  range. With no reachable planet, the action is disabled with
+  the "no planets in drive range" tooltip.
+- **Load**: requires the orbit planet to be owned by the player
+  or unowned (`controller/ship_group.go:215`) and the ship class
+  to have a cargo block (`shipGroupLoad:220`). The dropdown is
+  pinned to the existing cargo type when the group is already
+  partially loaded (the engine refuses cargo-type changes at
+  `shipGroupLoad:223`).
+- **Unload**: requires non-empty cargo. Colonists (`COL`) over a
+  foreign planet are blocked (`shipGroupUnload:283`), with the
+  matching tooltip in the disabled state.
+- **Modernize**: requires the orbit planet to be own/unowned
+  (`shipGroupUpgrade:29`) and at least one block whose race tech
+  exceeds the group tech (otherwise nothing can be upgraded).
+- **Dismantle**: always available in orbit. When the orbit is
+  over a foreign planet AND the group carries colonists, the
+  inline form replaces the normal "confirm" with "confirm —
+  colonists die"; the player has to click twice to commit
+  (engine reference `shipGroupDismantle:177-179` — over a
+  foreign planet, `UnloadColonists` is not called and the
+  cargo is lost).
+- **Transfer**: requires at least one non-extinct race other
+  than the local player (sourced from
+  `GameReport.otherRaces`).
+- **Join Fleet**: existing-fleet picker is restricted to fleets
+  in the same orbit (`fleet.go:135-137`); creating a new fleet
+  always works.
+
+## Modernize cost preview
+
+The form's preview line calls
+`core.blockUpgradeCost({ blockMass, currentTech, targetTech })`
+once per ship block (drive, weapons, shields, cargo) and sums
+the per-ship totals before multiplying by the targeted ship
+count. Block masses come from the player's
+`ShipClassSummary` for the group's class:
+
+- Drive / shields / cargo block mass = the corresponding ship-
+  class field (raw value).
+- Weapons block mass = `core.weaponsBlockMass({ weapons,
+  armament })` (Phase 18 bridge); returns null on the invalid
+  weapons/armament pairing, in which case the row contributes
+  zero.
+
+For `tech === "ALL"` every block whose mass is non-zero
+contributes against the player's race tech as the target. For
+per-block tech (`DRIVE` / `WEAPONS` / `SHIELDS` / `CARGO`) only
+the chosen block contributes, with `level` as the target.
+
+The preview hides when the form is invalid (`tech !== "ALL"`
+with non-positive `level`) or when `Core` has not yet booted —
+the bridge call is the only source of truth, so we surface
+"preview unavailable" rather than fall back to a JS
+re-implementation that could drift from the engine.
+
+## Wire shape
+
+Every emitted command carries:
+
+- `id` — client-minted UUID (`crypto.randomUUID()`), used by the
+  order draft for status tracking; mirrored as
+  `CommandItem.cmdId` on the wire.
+- `groupId` — the source ship-group's UUID (or `newGroupId` when
+  the action is the second half of an implicit split). On the
+  wire it is the `id` field of every ship-group payload type.
+
+Per-action additional fields are documented on the
+`OrderCommand` union in
+`ui/frontend/src/sync/order-types.ts` next to the JSDoc for each
+variant.
+
+## Decisions baked into Phase 20
+
+- **`BlockUpgradeCost` migrated to `pkg/calc`**. The cost
+  formula previously lived in
+  `game/internal/controller/ship_group_upgrade.go`. To keep the
+  `ui/core/calc` bridge a wrapper around pure `pkg/calc/`
+  formulas, the function moved to `pkg/calc/ship.go` and the
+  controller now imports it (`controller/ship_group_upgrade.go`).
+- **`GameReport.otherRaces`**. The transfer-to-race picker reads
+  from a new `GameReport.otherRaces: string[]` field, populated
+  by walking `report.player[]` and excluding the local race plus
+  every `extinct` entry. Phase 22 (Races View) reuses the same
+  field.
+- **Stationed-ship rows are clickable**. The map deliberately
+  hides on-planet groups; the planet inspector's stationed-ship
+  rows now pivot the selection to the corresponding ship-group
+  variant so the actions panel is reachable from the standard
+  click flow.
diff --git a/ui/frontend/src/api/game-state.ts b/ui/frontend/src/api/game-state.ts
index 3078bc1..2475840 100644
--- a/ui/frontend/src/api/game-state.ts
+++ b/ui/frontend/src/api/game-state.ts
@@ -272,6 +272,18 @@ export interface GameReport {
 	incomingShipGroups: ReportIncomingShipGroup[];
 	unidentifiedShipGroups: ReportUnidentifiedShipGroup[];
 	localFleets: ReportLocalFleet[];
+	/**
+	 * otherRaces lists the names of every non-extinct race other than
+	 * the local player, sorted alphabetically. Drawn from the
+	 * `report.player[]` block in the FBS report (each `Player` row
+	 * carries an `extinct` flag). The ship-group inspector consumes
+	 * this list for the "transfer to race" picker; Phase 22's Races
+	 * View reuses the same field so the read shape is stable across
+	 * stages. Empty when the report has no `player` block (boot
+	 * state, history-mode snapshots) or when the local player is the
+	 * only non-extinct race.
+	 */
+	otherRaces: string[];
 }
 
 export async function fetchGameReport(
@@ -405,6 +417,7 @@ function decodeReport(report: Report): GameReport {
 	const raceName = report.race() ?? "";
 	const routes = decodeReportRoutes(report);
 	const localTech = findLocalPlayerTech(report, raceName);
+	const otherRaces = collectOtherRaces(report, raceName);
 	const localShipGroups = decodeLocalShipGroups(report);
 	const otherShipGroups = decodeOtherShipGroups(report);
 	const incomingShipGroups = decodeIncomingShipGroups(report);
@@ -429,6 +442,7 @@ function decodeReport(report: Report): GameReport {
 		incomingShipGroups,
 		unidentifiedShipGroups,
 		localFleets,
+		otherRaces,
 	};
 }
 
@@ -705,6 +719,27 @@ function findLocalPlayerTech(
 	return { drive: 0, weapons: 0, shields: 0, cargo: 0 };
 }
 
+/**
+ * collectOtherRaces walks the `report.player[]` block and returns
+ * the alphabetically-sorted names of every non-extinct race other
+ * than the local player. Used by `GameReport.otherRaces` to back the
+ * ship-group inspector's transfer-to-race picker (Phase 20) and the
+ * Races View list (Phase 22).
+ */
+function collectOtherRaces(report: Report, raceName: string): string[] {
+	const out: string[] = [];
+	for (let i = 0; i < report.playerLength(); i++) {
+		const player = report.player(i);
+		if (player === null) continue;
+		if (player.extinct()) continue;
+		const name = player.name() ?? "";
+		if (name === "" || name === raceName) continue;
+		out.push(name);
+	}
+	out.sort((a, b) => a.localeCompare(b));
+	return out;
+}
+
 /**
  * uuidToHiLo splits the canonical 36-character UUID string
  * (`xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`) into the two big-endian
diff --git a/ui/frontend/src/api/synthetic-report.ts b/ui/frontend/src/api/synthetic-report.ts
index a3b6915..d9e3398 100644
--- a/ui/frontend/src/api/synthetic-report.ts
+++ b/ui/frontend/src/api/synthetic-report.ts
@@ -102,6 +102,7 @@ interface SyntheticPlayer {
 	weapons: number;
 	shields: number;
 	cargo: number;
+	extinct?: boolean;
 }
 
 interface SyntheticShipGroup {
@@ -269,9 +270,25 @@ function decodeSyntheticReport(json: unknown): GameReport {
 		incomingShipGroups,
 		unidentifiedShipGroups,
 		localFleets,
+		otherRaces: collectOtherRacesFromSynthetic(root, race),
 	};
 }
 
+function collectOtherRacesFromSynthetic(
+	root: SyntheticReportRoot,
+	raceName: string,
+): string[] {
+	const out: string[] = [];
+	for (const player of root.player ?? []) {
+		if (player.extinct === true) continue;
+		const name = typeof player.name === "string" ? player.name : "";
+		if (name === "" || name === raceName) continue;
+		out.push(name);
+	}
+	out.sort((a, b) => a.localeCompare(b));
+	return out;
+}
+
 function toShipGroupTech(raw: Record<string, number> | undefined): ShipGroupTech {
 	const out: ShipGroupTech = { drive: 0, weapons: 0, shields: 0, cargo: 0 };
 	if (raw === undefined || raw === null) return out;
diff --git a/ui/frontend/src/lib/i18n/locales/en.ts b/ui/frontend/src/lib/i18n/locales/en.ts
index 8c37f75..df699b8 100644
--- a/ui/frontend/src/lib/i18n/locales/en.ts
+++ b/ui/frontend/src/lib/i18n/locales/en.ts
@@ -194,6 +194,14 @@ const en = {
 	"game.sidebar.order.label.cargo_route_remove": "remove {loadType} route from planet {source}",
 	"game.sidebar.order.label.ship_class_create": "design ship class {name}",
 	"game.sidebar.order.label.ship_class_remove": "remove ship class {name}",
+	"game.sidebar.order.label.ship_group_break": "split group {group} → {quantity} ships into new group",
+	"game.sidebar.order.label.ship_group_send": "send group {group} → planet {destination}",
+	"game.sidebar.order.label.ship_group_load": "load {cargo} × {quantity} onto group {group}",
+	"game.sidebar.order.label.ship_group_unload": "unload × {quantity} from group {group}",
+	"game.sidebar.order.label.ship_group_upgrade": "modernize group {group} {tech} → {level}",
+	"game.sidebar.order.label.ship_group_dismantle": "dismantle group {group}",
+	"game.sidebar.order.label.ship_group_transfer": "transfer group {group} → {acceptor}",
+	"game.sidebar.order.label.ship_group_join_fleet": "assign group {group} → fleet {fleet}",
 	"game.table.ship_classes.title": "ship classes",
 	"game.table.ship_classes.column.name": "name",
 	"game.table.ship_classes.column.drive": "drive",
@@ -276,6 +284,54 @@ const en = {
 	"game.inspector.ship_group.fleet.none": "—",
 	"game.inspector.ship_group.unidentified_no_data": "no data — only the radar blip is known",
 
+	"game.inspector.ship_group.action.split": "split",
+	"game.inspector.ship_group.action.send": "send",
+	"game.inspector.ship_group.action.load": "load",
+	"game.inspector.ship_group.action.unload": "unload",
+	"game.inspector.ship_group.action.modernize": "modernize",
+	"game.inspector.ship_group.action.dismantle": "dismantle",
+	"game.inspector.ship_group.action.transfer": "transfer",
+	"game.inspector.ship_group.action.join_fleet": "join fleet",
+	"game.inspector.ship_group.action.confirm": "confirm",
+	"game.inspector.ship_group.action.cancel": "cancel",
+	"game.inspector.ship_group.action.confirm_destroy": "confirm — colonists die",
+	"game.inspector.ship_group.action.disabled.not_in_orbit": "ships are busy ({state}); only orbiting groups accept actions",
+	"game.inspector.ship_group.action.disabled.no_reach": "no planets are within drive range",
+	"game.inspector.ship_group.action.disabled.no_drive": "this ship class has no drive block",
+	"game.inspector.ship_group.action.disabled.no_cargo_block": "this ship class has no cargo block",
+	"game.inspector.ship_group.action.disabled.no_planet": "the orbit planet is not visible",
+	"game.inspector.ship_group.action.disabled.foreign_planet": "this action is only available on your own or unowned planets",
+	"game.inspector.ship_group.action.disabled.empty_cargo": "the group is empty",
+	"game.inspector.ship_group.action.disabled.foreign_unload_col": "colonists cannot be unloaded over a foreign planet",
+	"game.inspector.ship_group.action.disabled.no_headroom": "the group's tech is already at your race level",
+	"game.inspector.ship_group.action.disabled.no_planet_stock": "the planet has no available stock of this cargo",
+	"game.inspector.ship_group.action.disabled.full_load": "the group is fully loaded",
+	"game.inspector.ship_group.action.disabled.no_other_races": "no other non-extinct races to transfer to",
+	"game.inspector.ship_group.action.disabled.unknown_class": "the ship class is missing from the report",
+	"game.inspector.ship_group.action.field.ships": "ships ({max} total)",
+	"game.inspector.ship_group.action.field.cargo": "cargo type",
+	"game.inspector.ship_group.action.field.quantity": "quantity",
+	"game.inspector.ship_group.action.field.level": "tech level",
+	"game.inspector.ship_group.action.field.tech": "tech",
+	"game.inspector.ship_group.action.field.acceptor": "acceptor",
+	"game.inspector.ship_group.action.field.fleet": "fleet name",
+	"game.inspector.ship_group.action.field.destination": "destination planet",
+	"game.inspector.ship_group.action.tech.all": "all blocks",
+	"game.inspector.ship_group.action.tech.drive": "drive",
+	"game.inspector.ship_group.action.tech.weapons": "weapons",
+	"game.inspector.ship_group.action.tech.shields": "shields",
+	"game.inspector.ship_group.action.tech.cargo": "cargo",
+	"game.inspector.ship_group.action.send.pick_prompt": "click a planet on the map (Esc to cancel)",
+	"game.inspector.ship_group.action.send.no_destination": "no destination chosen",
+	"game.inspector.ship_group.action.modernize.cost": "estimated cost: {cost}",
+	"game.inspector.ship_group.action.modernize.cost_unavailable": "cost preview unavailable",
+	"game.inspector.ship_group.action.dismantle.warning": "the group is over a foreign planet with colonists aboard — they will die",
+	"game.inspector.ship_group.action.fleet.create_new": "+ new fleet",
+	"game.inspector.ship_group.action.invalid.ship_count": "ships must be in the range 1…{max}",
+	"game.inspector.ship_group.action.invalid.quantity": "quantity must be greater than zero",
+	"game.inspector.ship_group.action.invalid.level": "level must be in ({current}, {max}]",
+	"game.inspector.ship_group.action.invalid.fleet_name": "fleet name does not match the entity-name rules",
+
 	"game.inspector.planet.ship_groups.title": "stationed ship groups",
 	"game.inspector.planet.ship_groups.row.count": "{count} ships",
 	"game.inspector.planet.ship_groups.row.mass": "mass {mass}",
diff --git a/ui/frontend/src/lib/i18n/locales/ru.ts b/ui/frontend/src/lib/i18n/locales/ru.ts
index 2f2512d..4f91cb8 100644
--- a/ui/frontend/src/lib/i18n/locales/ru.ts
+++ b/ui/frontend/src/lib/i18n/locales/ru.ts
@@ -195,6 +195,14 @@ const ru: Record<keyof typeof en, string> = {
 	"game.sidebar.order.label.cargo_route_remove": "удалить маршрут {loadType} с планеты {source}",
 	"game.sidebar.order.label.ship_class_create": "сконструировать класс корабля {name}",
 	"game.sidebar.order.label.ship_class_remove": "удалить класс корабля {name}",
+	"game.sidebar.order.label.ship_group_break": "разделить группу {group} → новая группа из {quantity} кораблей",
+	"game.sidebar.order.label.ship_group_send": "отправить группу {group} → планета {destination}",
+	"game.sidebar.order.label.ship_group_load": "загрузить {cargo} × {quantity} в группу {group}",
+	"game.sidebar.order.label.ship_group_unload": "выгрузить × {quantity} из группы {group}",
+	"game.sidebar.order.label.ship_group_upgrade": "модернизация группы {group} {tech} → {level}",
+	"game.sidebar.order.label.ship_group_dismantle": "разобрать группу {group}",
+	"game.sidebar.order.label.ship_group_transfer": "передать группу {group} → {acceptor}",
+	"game.sidebar.order.label.ship_group_join_fleet": "включить группу {group} → флот {fleet}",
 	"game.table.ship_classes.title": "классы кораблей",
 	"game.table.ship_classes.column.name": "название",
 	"game.table.ship_classes.column.drive": "двигатель",
@@ -277,6 +285,54 @@ const ru: Record<keyof typeof en, string> = {
 	"game.inspector.ship_group.fleet.none": "—",
 	"game.inspector.ship_group.unidentified_no_data": "данных нет — известны только координаты",
 
+	"game.inspector.ship_group.action.split": "разделить",
+	"game.inspector.ship_group.action.send": "отправить",
+	"game.inspector.ship_group.action.load": "загрузить",
+	"game.inspector.ship_group.action.unload": "выгрузить",
+	"game.inspector.ship_group.action.modernize": "модернизировать",
+	"game.inspector.ship_group.action.dismantle": "разобрать",
+	"game.inspector.ship_group.action.transfer": "передать",
+	"game.inspector.ship_group.action.join_fleet": "во флот",
+	"game.inspector.ship_group.action.confirm": "подтвердить",
+	"game.inspector.ship_group.action.cancel": "отмена",
+	"game.inspector.ship_group.action.confirm_destroy": "подтвердить — колонисты погибнут",
+	"game.inspector.ship_group.action.disabled.not_in_orbit": "корабли заняты ({state}); действия доступны только на орбите",
+	"game.inspector.ship_group.action.disabled.no_reach": "в радиусе двигателей нет планет",
+	"game.inspector.ship_group.action.disabled.no_drive": "у класса корабля нет блока двигателей",
+	"game.inspector.ship_group.action.disabled.no_cargo_block": "у класса корабля нет грузового отсека",
+	"game.inspector.ship_group.action.disabled.no_planet": "планета орбиты не видна",
+	"game.inspector.ship_group.action.disabled.foreign_planet": "действие доступно только над вашей или ничейной планетой",
+	"game.inspector.ship_group.action.disabled.empty_cargo": "трюм пуст",
+	"game.inspector.ship_group.action.disabled.foreign_unload_col": "колонистов нельзя высадить на чужой планете",
+	"game.inspector.ship_group.action.disabled.no_headroom": "технологии группы уже на вашем расовом уровне",
+	"game.inspector.ship_group.action.disabled.no_planet_stock": "на планете нет такого ресурса",
+	"game.inspector.ship_group.action.disabled.full_load": "трюм полностью заполнен",
+	"game.inspector.ship_group.action.disabled.no_other_races": "нет других нерасправленных рас для передачи",
+	"game.inspector.ship_group.action.disabled.unknown_class": "класс корабля не найден в отчёте",
+	"game.inspector.ship_group.action.field.ships": "кораблей (всего {max})",
+	"game.inspector.ship_group.action.field.cargo": "тип груза",
+	"game.inspector.ship_group.action.field.quantity": "количество",
+	"game.inspector.ship_group.action.field.level": "уровень технологии",
+	"game.inspector.ship_group.action.field.tech": "технология",
+	"game.inspector.ship_group.action.field.acceptor": "получатель",
+	"game.inspector.ship_group.action.field.fleet": "имя флота",
+	"game.inspector.ship_group.action.field.destination": "планета назначения",
+	"game.inspector.ship_group.action.tech.all": "все блоки",
+	"game.inspector.ship_group.action.tech.drive": "двигатели",
+	"game.inspector.ship_group.action.tech.weapons": "оружие",
+	"game.inspector.ship_group.action.tech.shields": "защита",
+	"game.inspector.ship_group.action.tech.cargo": "груз",
+	"game.inspector.ship_group.action.send.pick_prompt": "выберите планету на карте (Esc — отмена)",
+	"game.inspector.ship_group.action.send.no_destination": "планета не выбрана",
+	"game.inspector.ship_group.action.modernize.cost": "ожидаемая стоимость: {cost}",
+	"game.inspector.ship_group.action.modernize.cost_unavailable": "предпросмотр недоступен",
+	"game.inspector.ship_group.action.dismantle.warning": "группа над чужой планетой везёт колонистов — они погибнут",
+	"game.inspector.ship_group.action.fleet.create_new": "+ новый флот",
+	"game.inspector.ship_group.action.invalid.ship_count": "число кораблей должно быть в диапазоне 1…{max}",
+	"game.inspector.ship_group.action.invalid.quantity": "количество должно быть больше нуля",
+	"game.inspector.ship_group.action.invalid.level": "уровень должен быть в ({current}, {max}]",
+	"game.inspector.ship_group.action.invalid.fleet_name": "имя флота не соответствует правилам имён сущностей",
+
 	"game.inspector.planet.ship_groups.title": "корабли на орбите",
 	"game.inspector.planet.ship_groups.row.count": "{count} кораблей",
 	"game.inspector.planet.ship_groups.row.mass": "масса {mass}",
diff --git a/ui/frontend/src/lib/inspectors/planet/ship-groups.svelte b/ui/frontend/src/lib/inspectors/planet/ship-groups.svelte
index e5131c5..fe5270b 100644
--- a/ui/frontend/src/lib/inspectors/planet/ship-groups.svelte
+++ b/ui/frontend/src/lib/inspectors/planet/ship-groups.svelte
@@ -1,29 +1,37 @@
 <!--
-Phase 19 read-only "ship groups stationed here" subsection of the
-planet inspector. Phase 19 originally rendered every in-orbit group
-as an offset point near its planet on the map, which crowded the
-canvas to the point of unreadability. The map now hides on-planet
-groups and the planet inspector lists them instead — one row per
-group, showing its race, class, ship count, and mass.
-
-Race attribution is best-effort:
+"Ship groups stationed here" subsection of the planet inspector.
+The map deliberately hides on-planet groups (rendering them as
+offset points crowds the canvas), so this list is the player's
+view of which fleets sit in this orbit. Race attribution is
+best-effort:
   - LocalGroup → the player's own race (`localRace` prop).
   - OtherGroup on an `other`-kind planet → the planet's owner.
   - OtherGroup elsewhere → "foreign" placeholder; the engine's
     typed contract does not carry per-group ownership outside
     battle rosters.
 
-Rows are intentionally non-interactive in Phase 19. Phase 21+ will
-deliver a full ship-groups table view; clicking a row will then
-deep-link into that table with a `(planet, race)` filter pre-applied.
+Phase 20 makes own-ship rows interactive: clicking a row pivots
+the inspector to the corresponding ship-group inspector through
+the shared `SelectionStore`. The actions panel mounts on top of
+the existing ship-group inspector, so the row is the on-planet
+entry point for Send / Load / Modernize / etc. Foreign rows stay
+non-interactive — there are no actions to drive against another
+race's fleet. Phase 21+ will reuse the same row shape inside the
+ship-groups table view with an additional `(planet, race)` filter.
 -->
 <script lang="ts">
+	import { getContext } from "svelte";
+
 	import type {
 		ReportLocalShipGroup,
 		ReportOtherShipGroup,
 		ReportPlanet,
 	} from "../../../api/game-state";
 	import { i18n } from "$lib/i18n/index.svelte";
+	import {
+		SELECTION_CONTEXT_KEY,
+		type SelectionStore,
+	} from "$lib/selection.svelte";
 
 	type Props = {
 		planet: ReportPlanet;
@@ -33,12 +41,18 @@ deep-link into that table with a `(planet, race)` filter pre-applied.
 	};
 	let { planet, localShipGroups, otherShipGroups, localRace }: Props = $props();
 
+	const selection = getContext<SelectionStore | undefined>(
+		SELECTION_CONTEXT_KEY,
+	);
+
 	interface StationedRow {
 		key: string;
 		race: string;
 		class: string;
 		count: number;
 		mass: number;
+		selectable: boolean;
+		groupId: string | null;
 	}
 
 	const stationedRows: StationedRow[] = $derived.by(() => {
@@ -52,6 +66,8 @@ deep-link into that table with a `(planet, race)` filter pre-applied.
 				class: g.class,
 				count: g.count,
 				mass: g.mass,
+				selectable: true,
+				groupId: g.id,
 			});
 		}
 		const foreignRace =
@@ -67,6 +83,8 @@ deep-link into that table with a `(planet, race)` filter pre-applied.
 				class: g.class,
 				count: g.count,
 				mass: g.mass,
+				selectable: false,
+				groupId: null,
 			});
 		}
 		return rows;
@@ -75,6 +93,11 @@ deep-link into that table with a `(planet, race)` filter pre-applied.
 	function formatNumber(value: number): string {
 		return value.toLocaleString(undefined, { maximumFractionDigits: 2 });
 	}
+
+	function selectLocalGroup(groupId: string): void {
+		if (selection === undefined) return;
+		selection.selectShipGroup({ variant: "local", id: groupId });
+	}
 </script>
 
 {#if stationedRows.length > 0}
@@ -83,20 +106,45 @@ deep-link into that table with a `(planet, race)` filter pre-applied.
 		<ul class="rows">
 			{#each stationedRows as row (row.key)}
 				<li class="row" data-testid="inspector-planet-ship-groups-row">
-					<span class="race" data-testid="inspector-planet-ship-groups-race">
-						{row.race}
-					</span>
-					<span class="class">{row.class}</span>
-					<span class="count">
-						{i18n.t("game.inspector.planet.ship_groups.row.count", {
-							count: String(row.count),
-						})}
-					</span>
-					<span class="mass">
-						{i18n.t("game.inspector.planet.ship_groups.row.mass", {
-							mass: formatNumber(row.mass),
-						})}
-					</span>
+					{#if row.selectable && row.groupId !== null}
+						{@const groupId = row.groupId}
+						<button
+							type="button"
+							class="select"
+							data-testid="inspector-planet-ship-groups-select"
+							onclick={() => selectLocalGroup(groupId)}
+						>
+							<span class="race" data-testid="inspector-planet-ship-groups-race">
+								{row.race}
+							</span>
+							<span class="class">{row.class}</span>
+							<span class="count">
+								{i18n.t("game.inspector.planet.ship_groups.row.count", {
+									count: String(row.count),
+								})}
+							</span>
+							<span class="mass">
+								{i18n.t("game.inspector.planet.ship_groups.row.mass", {
+									mass: formatNumber(row.mass),
+								})}
+							</span>
+						</button>
+					{:else}
+						<span class="race" data-testid="inspector-planet-ship-groups-race">
+							{row.race}
+						</span>
+						<span class="class">{row.class}</span>
+						<span class="count">
+							{i18n.t("game.inspector.planet.ship_groups.row.count", {
+								count: String(row.count),
+							})}
+						</span>
+						<span class="mass">
+							{i18n.t("game.inspector.planet.ship_groups.row.mass", {
+								mass: formatNumber(row.mass),
+							})}
+						</span>
+					{/if}
 				</li>
 			{/each}
 		</ul>
@@ -125,11 +173,30 @@ deep-link into that table with a `(planet, race)` filter pre-applied.
 		gap: 0.2rem;
 	}
 	.row {
+		display: block;
+		font-size: 0.85rem;
+		font-variant-numeric: tabular-nums;
+	}
+	.row > span,
+	.row > .select {
 		display: grid;
 		grid-template-columns: 1fr 1fr auto auto;
 		gap: 0.5rem;
-		font-size: 0.85rem;
-		font-variant-numeric: tabular-nums;
+	}
+	.select {
+		width: 100%;
+		font: inherit;
+		text-align: left;
+		background: transparent;
+		color: inherit;
+		border: 1px solid transparent;
+		border-radius: 3px;
+		padding: 0.15rem 0.3rem;
+		cursor: pointer;
+	}
+	.select:hover {
+		border-color: #2a3150;
+		background: #0d1224;
 	}
 	.race {
 		font-weight: 600;
diff --git a/ui/frontend/src/lib/inspectors/ship-group-sheet.svelte b/ui/frontend/src/lib/inspectors/ship-group-sheet.svelte
index 314785c..26e1509 100644
--- a/ui/frontend/src/lib/inspectors/ship-group-sheet.svelte
+++ b/ui/frontend/src/lib/inspectors/ship-group-sheet.svelte
@@ -6,17 +6,44 @@ mounted by the in-game shell layout only while the active tool is
 `map` so it does not stack on top of the calc / order overlays.
 -->
 <script lang="ts">
-	import type { ReportPlanet } from "../../api/game-state";
+	import type {
+		ReportLocalFleet,
+		ReportPlanet,
+		ShipClassSummary,
+	} from "../../api/game-state";
 	import { i18n } from "$lib/i18n/index.svelte";
 	import ShipGroup, { type ShipGroupSelection } from "./ship-group.svelte";
 
 	type Props = {
 		selection: ShipGroupSelection | null;
 		planets: ReportPlanet[];
+		localShipClass: ShipClassSummary[];
+		localFleets: ReportLocalFleet[];
+		otherRaces: string[];
+		mapWidth: number;
+		mapHeight: number;
+		localPlayerDrive: number;
+		localPlayerWeapons: number;
+		localPlayerShields: number;
+		localPlayerCargo: number;
 		onMap: boolean;
 		onClose: () => void;
 	};
-	let { selection, planets, onMap, onClose }: Props = $props();
+	let {
+		selection,
+		planets,
+		localShipClass,
+		localFleets,
+		otherRaces,
+		mapWidth,
+		mapHeight,
+		localPlayerDrive,
+		localPlayerWeapons,
+		localPlayerShields,
+		localPlayerCargo,
+		onMap,
+		onClose,
+	}: Props = $props();
 </script>
 
 {#if selection !== null && onMap}
@@ -34,7 +61,19 @@ mounted by the in-game shell layout only while the active tool is
 		>
 			✕
 		</button>
-		<ShipGroup {selection} {planets} />
+		<ShipGroup
+			{selection}
+			{planets}
+			{localShipClass}
+			{localFleets}
+			{otherRaces}
+			{mapWidth}
+			{mapHeight}
+			{localPlayerDrive}
+			{localPlayerWeapons}
+			{localPlayerShields}
+			{localPlayerCargo}
+		/>
 	</section>
 {/if}
 
diff --git a/ui/frontend/src/lib/inspectors/ship-group.svelte b/ui/frontend/src/lib/inspectors/ship-group.svelte
index dc2d40a..8c5a440 100644
--- a/ui/frontend/src/lib/inspectors/ship-group.svelte
+++ b/ui/frontend/src/lib/inspectors/ship-group.svelte
@@ -12,12 +12,15 @@ variant — for Phase 19 the inspector is intentionally read-only.
 <script lang="ts">
 	import type {
 		ReportIncomingShipGroup,
+		ReportLocalFleet,
 		ReportLocalShipGroup,
 		ReportOtherShipGroup,
 		ReportPlanet,
 		ReportUnidentifiedShipGroup,
+		ShipClassSummary,
 	} from "../../api/game-state";
 	import { i18n, type TranslationKey } from "$lib/i18n/index.svelte";
+	import Actions from "./ship-group/actions.svelte";
 
 	export type ShipGroupSelection =
 		| { variant: "local"; group: ReportLocalShipGroup }
@@ -28,8 +31,29 @@ variant — for Phase 19 the inspector is intentionally read-only.
 	type Props = {
 		selection: ShipGroupSelection;
 		planets: ReportPlanet[];
+		localShipClass?: ShipClassSummary[];
+		localFleets?: ReportLocalFleet[];
+		otherRaces?: string[];
+		mapWidth?: number;
+		mapHeight?: number;
+		localPlayerDrive?: number;
+		localPlayerWeapons?: number;
+		localPlayerShields?: number;
+		localPlayerCargo?: number;
 	};
-	let { selection, planets }: Props = $props();
+	let {
+		selection,
+		planets,
+		localShipClass = [],
+		localFleets = [],
+		otherRaces = [],
+		mapWidth = 1,
+		mapHeight = 1,
+		localPlayerDrive = 0,
+		localPlayerWeapons = 0,
+		localPlayerShields = 0,
+		localPlayerCargo = 0,
+	}: Props = $props();
 
 	const kindKeyMap: Record<ShipGroupSelection["variant"], TranslationKey> = {
 		local: "game.inspector.ship_group.kind.local",
@@ -86,6 +110,22 @@ variant — for Phase 19 the inspector is intentionally read-only.
 		{/if}
 	</header>
 
+	{#if selection.variant === "local"}
+		<Actions
+			group={selection.group}
+			{planets}
+			{localShipClass}
+			{localFleets}
+			{otherRaces}
+			{mapWidth}
+			{mapHeight}
+			{localPlayerDrive}
+			{localPlayerWeapons}
+			{localPlayerShields}
+			{localPlayerCargo}
+		/>
+	{/if}
+
 	{#if selection.variant === "local" || selection.variant === "other"}
 		{@const g = selection.group}
 		{@const onPlanet = g.origin === null || g.range === null}
diff --git a/ui/frontend/src/lib/inspectors/ship-group/actions.svelte b/ui/frontend/src/lib/inspectors/ship-group/actions.svelte
new file mode 100644
index 0000000..1025fad
--- /dev/null
+++ b/ui/frontend/src/lib/inspectors/ship-group/actions.svelte
@@ -0,0 +1,1154 @@
+<!--
+Phase 20 ship-group action panel.
+
+Mounted by `lib/inspectors/ship-group.svelte` for `selection.variant
+=== "local"`. Renders eight inline forms — Split, Send, Load, Unload,
+Modernize, Dismantle, Transfer, Join Fleet — each gated by the same
+state-and-context predicates that the engine enforces server-side. All
+real actions either append a single command to the local order draft
+or, when the player chose fewer ships than the group holds, prepend
+an implicit `breakShipGroup` and route the action at the freshly-
+minted sub-group ID.
+
+The component owns the open/closed state for each form (so opening
+one closes the others), the ephemeral form fields, and the live
+modernize cost preview backed by `core.blockUpgradeCost`.
+-->
+<script lang="ts">
+	import { getContext } from "svelte";
+
+	import type {
+		ReportLocalFleet,
+		ReportLocalShipGroup,
+		ReportPlanet,
+		ShipClassSummary,
+	} from "../../../api/game-state";
+	import { i18n, type TranslationKey } from "$lib/i18n/index.svelte";
+	import { CORE_CONTEXT_KEY, type CoreHandle } from "$lib/core-context.svelte";
+	import {
+		MAP_PICK_CONTEXT_KEY,
+		type MapPickService,
+	} from "$lib/map-pick.svelte";
+	import { torusShortestDelta } from "../../../map/math";
+	import {
+		ORDER_DRAFT_CONTEXT_KEY,
+		OrderDraftStore,
+	} from "../../../sync/order-draft.svelte";
+	import {
+		SHIP_GROUP_CARGO_VALUES,
+		SHIP_GROUP_UPGRADE_TECH_VALUES,
+		type OrderCommand,
+		type ShipGroupCargo,
+		type ShipGroupUpgradeTech,
+	} from "../../../sync/order-types";
+	import { validateEntityName } from "$lib/util/entity-name";
+
+	type Props = {
+		group: ReportLocalShipGroup;
+		planets: ReportPlanet[];
+		localShipClass: ShipClassSummary[];
+		localFleets: ReportLocalFleet[];
+		otherRaces: string[];
+		mapWidth: number;
+		mapHeight: number;
+		localPlayerDrive: number;
+		localPlayerWeapons: number;
+		localPlayerShields: number;
+		localPlayerCargo: number;
+	};
+	let {
+		group,
+		planets,
+		localShipClass,
+		localFleets,
+		otherRaces,
+		mapWidth,
+		mapHeight,
+		localPlayerDrive,
+		localPlayerWeapons,
+		localPlayerShields,
+		localPlayerCargo,
+	}: Props = $props();
+
+	const draft = getContext<OrderDraftStore | undefined>(
+		ORDER_DRAFT_CONTEXT_KEY,
+	);
+	const pick = getContext<MapPickService | undefined>(MAP_PICK_CONTEXT_KEY);
+	const coreHandle = getContext<CoreHandle | undefined>(CORE_CONTEXT_KEY);
+
+	type FormName =
+		| "split"
+		| "send"
+		| "load"
+		| "unload"
+		| "modernize"
+		| "dismantle"
+		| "transfer"
+		| "joinFleet";
+
+	let openForm: FormName | null = $state(null);
+
+	// Per-form ephemeral state. Resets via the form-open helpers below
+	// so a stale value from a previous selection cannot leak into the
+	// next one.
+	let splitShips = $state(1);
+	let sendShips = $state(1);
+	let sendDestination: number | null = $state(null);
+	let sendPicking = $state(false);
+	let loadShips = $state(1);
+	let loadCargo: ShipGroupCargo = $state("COL");
+	let loadQuantity = $state(0);
+	let unloadShips = $state(1);
+	let unloadQuantity = $state(0);
+	let modernizeShips = $state(1);
+	let modernizeTech: ShipGroupUpgradeTech = $state("ALL");
+	let modernizeLevel = $state(0);
+	let dismantleShips = $state(1);
+	let dismantleConfirmed = $state(false);
+	let transferShips = $state(1);
+	let transferAcceptor = $state("");
+	let joinFleetMode: "existing" | "new" = $state("new");
+	let joinFleetExisting = $state("");
+	let joinFleetNew = $state("");
+
+	// Reset all per-form state whenever the selected group changes so a
+	// stale form does not leak across selection switches.
+	$effect(() => {
+		void group.id;
+		openForm = null;
+	});
+
+	const inOrbit = $derived(group.state === "In_Orbit");
+	const orbitPlanet = $derived(
+		inOrbit ? (planets.find((p) => p.number === group.destination) ?? null) : null,
+	);
+	const shipClass = $derived(
+		localShipClass.find((sc) => sc.name === group.class) ?? null,
+	);
+	const ownPlanet = $derived(orbitPlanet?.kind === "local");
+	const uninhabitedPlanet = $derived(orbitPlanet?.kind === "uninhabited");
+	const friendlyPlanet = $derived(ownPlanet || uninhabitedPlanet);
+	const hasCargoBlock = $derived(shipClass !== null && shipClass.cargo > 0);
+	const hasDriveBlock = $derived(shipClass !== null && shipClass.drive > 0);
+	const reach = $derived(40 * localPlayerDrive);
+	const cargoLoaded = $derived(group.cargo !== "NONE" && group.load > 0);
+	const carryingColonists = $derived(group.cargo === "COL" && group.load > 0);
+
+	const reachableSet = $derived.by(() => {
+		const ids = new Set<number>();
+		if (!inOrbit || !hasDriveBlock || reach <= 0 || orbitPlanet === null)
+			return ids;
+		for (const candidate of planets) {
+			if (candidate.number === orbitPlanet.number) continue;
+			const dx = torusShortestDelta(orbitPlanet.x, candidate.x, mapWidth);
+			const dy = torusShortestDelta(orbitPlanet.y, candidate.y, mapHeight);
+			if (Math.hypot(dx, dy) <= reach) ids.add(candidate.number);
+		}
+		return ids;
+	});
+
+	const techHeadroom = $derived.by(() => {
+		// At least one block must have race tech > group tech AND a non-
+		// zero block mass for modernize to do anything (engine refuses
+		// when the requested block has zero mass — see
+		// controller/ship_group_upgrade.go:54).
+		if (shipClass === null) return false;
+		const blocks: Array<[number, number, number]> = [
+			[shipClass.drive, group.tech.drive, localPlayerDrive],
+			[shipClass.shields, group.tech.shields, localPlayerShields],
+			[shipClass.cargo, group.tech.cargo, localPlayerCargo],
+		];
+		// Weapons block mass requires the bridge.
+		const core = coreHandle?.core ?? null;
+		if (core !== null) {
+			const wm = core.weaponsBlockMass({
+				weapons: shipClass.weapons,
+				armament: shipClass.armament,
+			});
+			if (wm !== null) blocks.push([wm, group.tech.weapons, localPlayerWeapons]);
+		} else if (shipClass.weapons > 0) {
+			// Without Core, fall back to a weak heuristic: if weapons > 0
+			// the block exists. The engine still re-validates server-
+			// side so a false-positive only delays the rejection.
+			blocks.push([1, group.tech.weapons, localPlayerWeapons]);
+		}
+		return blocks.some(
+			([mass, current, race]) => mass > 0 && race > current,
+		);
+	});
+
+	const planetStock = $derived.by(() => {
+		if (orbitPlanet === null || orbitPlanet.kind === "unidentified") {
+			return { COL: 0, CAP: 0, MAT: 0 };
+		}
+		return {
+			COL: orbitPlanet.colonists ?? 0,
+			CAP: orbitPlanet.industryStockpile ?? 0,
+			MAT: orbitPlanet.materialsStockpile ?? 0,
+		};
+	});
+
+	const cargoCapacityPerShip = $derived.by(() => {
+		const core = coreHandle?.core ?? null;
+		if (core === null || shipClass === null) return null;
+		return core.cargoCapacity({
+			cargo: shipClass.cargo,
+			cargoTech: localPlayerCargo,
+		});
+	});
+
+	const groupCapacity = $derived(
+		cargoCapacityPerShip === null
+			? null
+			: cargoCapacityPerShip * group.count,
+	);
+	const freeCapacity = $derived(
+		groupCapacity === null ? null : Math.max(0, groupCapacity - group.load),
+	);
+
+	const fleetsOnSamePlanet = $derived(
+		localFleets.filter(
+			(f) =>
+				f.state === "In_Orbit" &&
+				f.destination === group.destination &&
+				f.origin === null,
+		),
+	);
+
+	function disabledStateTooltip(): string | null {
+		if (!inOrbit) {
+			return i18n.t(
+				"game.inspector.ship_group.action.disabled.not_in_orbit",
+				{ state: group.state },
+			);
+		}
+		return null;
+	}
+
+	function reasonTooltip(reason: TranslationKey | null): string | null {
+		return reason === null ? null : i18n.t(reason);
+	}
+
+	const splitDisabledReason = $derived(
+		!inOrbit
+			? "game.inspector.ship_group.action.disabled.not_in_orbit"
+			: group.count < 2
+				? "game.inspector.ship_group.action.invalid.ship_count"
+				: null,
+	);
+	const sendDisabledReason = $derived.by((): TranslationKey | null => {
+		if (!inOrbit) return "game.inspector.ship_group.action.disabled.not_in_orbit";
+		if (!hasDriveBlock) return "game.inspector.ship_group.action.disabled.no_drive";
+		if (orbitPlanet === null) return "game.inspector.ship_group.action.disabled.no_planet";
+		if (reachableSet.size === 0) return "game.inspector.ship_group.action.disabled.no_reach";
+		return null;
+	});
+	const loadDisabledReason = $derived.by((): TranslationKey | null => {
+		if (!inOrbit) return "game.inspector.ship_group.action.disabled.not_in_orbit";
+		if (!hasCargoBlock) return "game.inspector.ship_group.action.disabled.no_cargo_block";
+		if (orbitPlanet === null) return "game.inspector.ship_group.action.disabled.no_planet";
+		if (!friendlyPlanet) return "game.inspector.ship_group.action.disabled.foreign_planet";
+		if (freeCapacity !== null && freeCapacity <= 0)
+			return "game.inspector.ship_group.action.disabled.full_load";
+		const stock = planetStock;
+		if (stock.COL <= 0 && stock.CAP <= 0 && stock.MAT <= 0)
+			return "game.inspector.ship_group.action.disabled.no_planet_stock";
+		return null;
+	});
+	const unloadDisabledReason = $derived.by((): TranslationKey | null => {
+		if (!inOrbit) return "game.inspector.ship_group.action.disabled.not_in_orbit";
+		if (!hasCargoBlock) return "game.inspector.ship_group.action.disabled.no_cargo_block";
+		if (!cargoLoaded) return "game.inspector.ship_group.action.disabled.empty_cargo";
+		if (group.cargo === "COL" && !ownPlanet && !uninhabitedPlanet)
+			return "game.inspector.ship_group.action.disabled.foreign_unload_col";
+		return null;
+	});
+	const modernizeDisabledReason = $derived.by((): TranslationKey | null => {
+		if (!inOrbit) return "game.inspector.ship_group.action.disabled.not_in_orbit";
+		if (orbitPlanet === null) return "game.inspector.ship_group.action.disabled.no_planet";
+		if (!friendlyPlanet) return "game.inspector.ship_group.action.disabled.foreign_planet";
+		if (shipClass === null) return "game.inspector.ship_group.action.disabled.unknown_class";
+		if (!techHeadroom) return "game.inspector.ship_group.action.disabled.no_headroom";
+		return null;
+	});
+	const dismantleDisabledReason = $derived.by((): TranslationKey | null => {
+		if (!inOrbit) return "game.inspector.ship_group.action.disabled.not_in_orbit";
+		return null;
+	});
+	const transferDisabledReason = $derived.by((): TranslationKey | null => {
+		if (!inOrbit) return "game.inspector.ship_group.action.disabled.not_in_orbit";
+		if (otherRaces.length === 0)
+			return "game.inspector.ship_group.action.disabled.no_other_races";
+		return null;
+	});
+	const joinFleetDisabledReason = $derived.by((): TranslationKey | null => {
+		if (!inOrbit) return "game.inspector.ship_group.action.disabled.not_in_orbit";
+		return null;
+	});
+
+	function maxShips(): number {
+		return group.count;
+	}
+
+	function clampShips(value: number): number {
+		if (!Number.isFinite(value)) return 1;
+		const v = Math.floor(value);
+		if (v < 1) return 1;
+		if (v > group.count) return group.count;
+		return v;
+	}
+
+	function openSplit(): void {
+		closeOthers("split");
+		splitShips = Math.max(1, Math.min(Math.floor(group.count / 2), group.count - 1));
+	}
+	function openSend(): void {
+		closeOthers("send");
+		sendShips = group.count;
+		sendDestination = null;
+	}
+	function openLoad(): void {
+		closeOthers("load");
+		loadShips = group.count;
+		// Initialise cargo type to whatever the group already carries
+		// so the validator does not require an extra click; if empty,
+		// default to colonists (the highest priority cargo on routes).
+		loadCargo = group.cargo === "NONE" ? "COL" : (group.cargo as ShipGroupCargo);
+		loadQuantity = 0;
+	}
+	function openUnload(): void {
+		closeOthers("unload");
+		unloadShips = group.count;
+		unloadQuantity = group.load;
+	}
+	function openModernize(): void {
+		closeOthers("modernize");
+		modernizeShips = group.count;
+		modernizeTech = "ALL";
+		modernizeLevel = 0;
+	}
+	function openDismantle(): void {
+		closeOthers("dismantle");
+		dismantleShips = group.count;
+		dismantleConfirmed = false;
+	}
+	function openTransfer(): void {
+		closeOthers("transfer");
+		transferShips = group.count;
+		transferAcceptor = otherRaces[0] ?? "";
+	}
+	function openJoinFleet(): void {
+		closeOthers("joinFleet");
+		const candidates = fleetsOnSamePlanet;
+		joinFleetMode = candidates.length > 0 ? "existing" : "new";
+		joinFleetExisting = candidates[0]?.name ?? "";
+		joinFleetNew = "";
+	}
+
+	function closeOthers(target: FormName): void {
+		if (openForm === target) {
+			openForm = null;
+			return;
+		}
+		openForm = target;
+	}
+
+	function cancelForm(): void {
+		// Cancel any in-flight pick session so the renderer drops the
+		// dim mask before the form re-opens for a different action.
+		if (sendPicking) {
+			pick?.cancel();
+			sendPicking = false;
+		}
+		openForm = null;
+	}
+
+	function actionGroupId(targetShips: number): {
+		groupId: string;
+		breakCommand: OrderCommand | null;
+	} {
+		// When the action targets fewer ships than the group holds, the
+		// engine needs a fresh sub-group; we mint its UUID up front and
+		// emit a `breakShipGroup` command that carves it out before the
+		// real action runs against the new id.
+		if (targetShips >= group.count) {
+			return { groupId: group.id, breakCommand: null };
+		}
+		const newGroupId = crypto.randomUUID();
+		return {
+			groupId: newGroupId,
+			breakCommand: {
+				kind: "breakShipGroup",
+				id: crypto.randomUUID(),
+				groupId: group.id,
+				newGroupId,
+				quantity: targetShips,
+			},
+		};
+	}
+
+	async function emit(
+		breakCommand: OrderCommand | null,
+		action: OrderCommand,
+	): Promise<void> {
+		if (draft === undefined) return;
+		if (breakCommand !== null) await draft.add(breakCommand);
+		await draft.add(action);
+	}
+
+	async function confirmSplit(): Promise<void> {
+		const ships = clampShips(splitShips);
+		if (ships < 1 || ships >= group.count || draft === undefined) return;
+		await draft.add({
+			kind: "breakShipGroup",
+			id: crypto.randomUUID(),
+			groupId: group.id,
+			newGroupId: crypto.randomUUID(),
+			quantity: ships,
+		});
+		openForm = null;
+	}
+
+	async function startSendPick(): Promise<void> {
+		if (pick === undefined || sendPicking) return;
+		if (reachableSet.size === 0 || orbitPlanet === null) return;
+		sendPicking = true;
+		try {
+			const picked = await pick.pick({
+				sourcePlanetNumber: orbitPlanet.number,
+				reachableIds: reachableSet,
+			});
+			if (picked !== null) sendDestination = picked;
+		} finally {
+			sendPicking = false;
+		}
+	}
+
+	async function confirmSend(): Promise<void> {
+		if (sendDestination === null || draft === undefined) return;
+		const ships = clampShips(sendShips);
+		const { groupId, breakCommand } = actionGroupId(ships);
+		await emit(breakCommand, {
+			kind: "sendShipGroup",
+			id: crypto.randomUUID(),
+			groupId,
+			destinationPlanetNumber: sendDestination,
+		});
+		openForm = null;
+	}
+
+	async function confirmLoad(): Promise<void> {
+		const ships = clampShips(loadShips);
+		const quantity = Number(loadQuantity);
+		if (!(quantity > 0) || draft === undefined) return;
+		const { groupId, breakCommand } = actionGroupId(ships);
+		await emit(breakCommand, {
+			kind: "loadShipGroup",
+			id: crypto.randomUUID(),
+			groupId,
+			cargo: loadCargo,
+			quantity,
+		});
+		openForm = null;
+	}
+
+	async function confirmUnload(): Promise<void> {
+		const ships = clampShips(unloadShips);
+		const quantity = Number(unloadQuantity);
+		if (!(quantity > 0) || draft === undefined) return;
+		const { groupId, breakCommand } = actionGroupId(ships);
+		await emit(breakCommand, {
+			kind: "unloadShipGroup",
+			id: crypto.randomUUID(),
+			groupId,
+			quantity,
+		});
+		openForm = null;
+	}
+
+	async function confirmModernize(): Promise<void> {
+		if (draft === undefined) return;
+		const ships = clampShips(modernizeShips);
+		const tech = modernizeTech;
+		const level = tech === "ALL" ? 0 : Number(modernizeLevel);
+		if (tech !== "ALL" && !(level > 0)) return;
+		const { groupId, breakCommand } = actionGroupId(ships);
+		await emit(breakCommand, {
+			kind: "upgradeShipGroup",
+			id: crypto.randomUUID(),
+			groupId,
+			tech,
+			level,
+		});
+		openForm = null;
+	}
+
+	async function confirmDismantle(): Promise<void> {
+		if (draft === undefined) return;
+		const ships = clampShips(dismantleShips);
+		const subset = ships < group.count;
+		const colonistsOverForeign = !ownPlanet && !uninhabitedPlanet && subset
+			? group.cargo === "COL" && group.load > 0
+			: !ownPlanet && !uninhabitedPlanet && carryingColonists;
+		if (colonistsOverForeign && !dismantleConfirmed) {
+			dismantleConfirmed = true;
+			return;
+		}
+		const { groupId, breakCommand } = actionGroupId(ships);
+		await emit(breakCommand, {
+			kind: "dismantleShipGroup",
+			id: crypto.randomUUID(),
+			groupId,
+		});
+		openForm = null;
+	}
+
+	async function confirmTransfer(): Promise<void> {
+		if (draft === undefined) return;
+		const ships = clampShips(transferShips);
+		const acceptor = transferAcceptor.trim();
+		if (acceptor === "") return;
+		const { groupId, breakCommand } = actionGroupId(ships);
+		await emit(breakCommand, {
+			kind: "transferShipGroup",
+			id: crypto.randomUUID(),
+			groupId,
+			acceptor,
+		});
+		openForm = null;
+	}
+
+	async function confirmJoinFleet(): Promise<void> {
+		if (draft === undefined) return;
+		const name = joinFleetMode === "existing" ? joinFleetExisting : joinFleetNew;
+		if (!validateEntityName(name).ok) return;
+		await draft.add({
+			kind: "joinFleetShipGroup",
+			id: crypto.randomUUID(),
+			groupId: group.id,
+			name,
+		});
+		openForm = null;
+	}
+
+	const modernizeCostPreview = $derived.by(() => {
+		const core = coreHandle?.core ?? null;
+		if (core === null || shipClass === null) return null;
+		const ships = clampShips(modernizeShips);
+		const targets: Record<"DRIVE" | "WEAPONS" | "SHIELDS" | "CARGO", number> =
+			modernizeTech === "ALL"
+				? {
+						DRIVE: localPlayerDrive,
+						WEAPONS: localPlayerWeapons,
+						SHIELDS: localPlayerShields,
+						CARGO: localPlayerCargo,
+					}
+				: {
+						DRIVE: 0,
+						WEAPONS: 0,
+						SHIELDS: 0,
+						CARGO: 0,
+						[modernizeTech]: Number(modernizeLevel) || 0,
+					};
+		const weapons = core.weaponsBlockMass({
+			weapons: shipClass.weapons,
+			armament: shipClass.armament,
+		});
+		const blocks: Array<[number, number, number]> = [
+			[shipClass.drive, group.tech.drive, targets.DRIVE],
+			[weapons ?? 0, group.tech.weapons, targets.WEAPONS],
+			[shipClass.shields, group.tech.shields, targets.SHIELDS],
+			[shipClass.cargo, group.tech.cargo, targets.CARGO],
+		];
+		let perShip = 0;
+		for (const [mass, current, target] of blocks) {
+			if (target <= 0) continue;
+			perShip += core.blockUpgradeCost({
+				blockMass: mass,
+				currentTech: current,
+				targetTech: target,
+			});
+		}
+		if (perShip <= 0) return 0;
+		return perShip * ships;
+	});
+
+	const cargoLabelKey: Record<ShipGroupCargo, TranslationKey> = {
+		COL: "game.inspector.ship_group.cargo.col",
+		CAP: "game.inspector.ship_group.cargo.cap",
+		MAT: "game.inspector.ship_group.cargo.mat",
+	};
+	const techLabelKey: Record<ShipGroupUpgradeTech, TranslationKey> = {
+		ALL: "game.inspector.ship_group.action.tech.all",
+		DRIVE: "game.inspector.ship_group.action.tech.drive",
+		WEAPONS: "game.inspector.ship_group.action.tech.weapons",
+		SHIELDS: "game.inspector.ship_group.action.tech.shields",
+		CARGO: "game.inspector.ship_group.action.tech.cargo",
+	};
+
+	function formatNumber(value: number): string {
+		return value.toLocaleString(undefined, { maximumFractionDigits: 2 });
+	}
+</script>
+
+<section class="actions" data-testid="inspector-ship-group-actions">
+	<div class="row">
+		<button
+			type="button"
+			class="action"
+			data-testid="inspector-ship-group-action-split"
+			disabled={splitDisabledReason !== null || draft === undefined}
+			title={reasonTooltip(splitDisabledReason as TranslationKey | null) ?? ""}
+			onclick={openSplit}
+		>
+			{i18n.t("game.inspector.ship_group.action.split")}
+		</button>
+		<button
+			type="button"
+			class="action"
+			data-testid="inspector-ship-group-action-send"
+			disabled={sendDisabledReason !== null || draft === undefined}
+			title={reasonTooltip(sendDisabledReason) ?? ""}
+			onclick={openSend}
+		>
+			{i18n.t("game.inspector.ship_group.action.send")}
+		</button>
+		<button
+			type="button"
+			class="action"
+			data-testid="inspector-ship-group-action-load"
+			disabled={loadDisabledReason !== null || draft === undefined}
+			title={reasonTooltip(loadDisabledReason) ?? ""}
+			onclick={openLoad}
+		>
+			{i18n.t("game.inspector.ship_group.action.load")}
+		</button>
+		<button
+			type="button"
+			class="action"
+			data-testid="inspector-ship-group-action-unload"
+			disabled={unloadDisabledReason !== null || draft === undefined}
+			title={reasonTooltip(unloadDisabledReason) ?? ""}
+			onclick={openUnload}
+		>
+			{i18n.t("game.inspector.ship_group.action.unload")}
+		</button>
+		<button
+			type="button"
+			class="action"
+			data-testid="inspector-ship-group-action-modernize"
+			disabled={modernizeDisabledReason !== null || draft === undefined}
+			title={reasonTooltip(modernizeDisabledReason) ?? ""}
+			onclick={openModernize}
+		>
+			{i18n.t("game.inspector.ship_group.action.modernize")}
+		</button>
+		<button
+			type="button"
+			class="action"
+			data-testid="inspector-ship-group-action-dismantle"
+			disabled={dismantleDisabledReason !== null || draft === undefined}
+			title={reasonTooltip(dismantleDisabledReason) ?? ""}
+			onclick={openDismantle}
+		>
+			{i18n.t("game.inspector.ship_group.action.dismantle")}
+		</button>
+		<button
+			type="button"
+			class="action"
+			data-testid="inspector-ship-group-action-transfer"
+			disabled={transferDisabledReason !== null || draft === undefined}
+			title={reasonTooltip(transferDisabledReason) ?? ""}
+			onclick={openTransfer}
+		>
+			{i18n.t("game.inspector.ship_group.action.transfer")}
+		</button>
+		<button
+			type="button"
+			class="action"
+			data-testid="inspector-ship-group-action-join-fleet"
+			disabled={joinFleetDisabledReason !== null || draft === undefined}
+			title={reasonTooltip(joinFleetDisabledReason) ?? ""}
+			onclick={openJoinFleet}
+		>
+			{i18n.t("game.inspector.ship_group.action.join_fleet")}
+		</button>
+	</div>
+
+	{#if openForm === "split"}
+		<form class="form" data-testid="inspector-ship-group-form-split" onsubmit={(e) => { e.preventDefault(); void confirmSplit(); }}>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.ships", { max: String(maxShips()) })}
+				<input
+					type="number"
+					min="1"
+					max={String(group.count - 1)}
+					step="1"
+					data-testid="inspector-ship-group-form-split-ships"
+					bind:value={splitShips}
+				/>
+			</label>
+			<div class="form-actions">
+				<button type="button" data-testid="inspector-ship-group-form-split-cancel" onclick={cancelForm}>
+					{i18n.t("game.inspector.ship_group.action.cancel")}
+				</button>
+				<button
+					type="submit"
+					class="primary"
+					data-testid="inspector-ship-group-form-split-confirm"
+					disabled={splitShips < 1 || splitShips >= group.count}
+				>
+					{i18n.t("game.inspector.ship_group.action.confirm")}
+				</button>
+			</div>
+		</form>
+	{/if}
+
+	{#if openForm === "send"}
+		<form class="form" data-testid="inspector-ship-group-form-send" onsubmit={(e) => { e.preventDefault(); void confirmSend(); }}>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.ships", { max: String(maxShips()) })}
+				<input
+					type="number"
+					min="1"
+					max={String(group.count)}
+					step="1"
+					data-testid="inspector-ship-group-form-send-ships"
+					bind:value={sendShips}
+				/>
+			</label>
+			<div class="destination-row">
+				<span class="label">{i18n.t("game.inspector.ship_group.action.field.destination")}</span>
+				<span data-testid="inspector-ship-group-form-send-destination">
+					{#if sendDestination !== null}
+						{planets.find((p) => p.number === sendDestination)?.name ?? `#${sendDestination}`}
+					{:else}
+						{i18n.t("game.inspector.ship_group.action.send.no_destination")}
+					{/if}
+				</span>
+				<button
+					type="button"
+					data-testid="inspector-ship-group-form-send-pick"
+					disabled={sendPicking || pick === undefined}
+					onclick={() => void startSendPick()}
+				>
+					{sendPicking
+						? i18n.t("game.inspector.ship_group.action.send.pick_prompt")
+						: i18n.t("game.inspector.ship_group.action.field.destination")}
+				</button>
+			</div>
+			<div class="form-actions">
+				<button type="button" data-testid="inspector-ship-group-form-send-cancel" onclick={cancelForm}>
+					{i18n.t("game.inspector.ship_group.action.cancel")}
+				</button>
+				<button
+					type="submit"
+					class="primary"
+					data-testid="inspector-ship-group-form-send-confirm"
+					disabled={sendDestination === null}
+				>
+					{i18n.t("game.inspector.ship_group.action.confirm")}
+				</button>
+			</div>
+		</form>
+	{/if}
+
+	{#if openForm === "load"}
+		<form class="form" data-testid="inspector-ship-group-form-load" onsubmit={(e) => { e.preventDefault(); void confirmLoad(); }}>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.ships", { max: String(maxShips()) })}
+				<input
+					type="number"
+					min="1"
+					max={String(group.count)}
+					step="1"
+					data-testid="inspector-ship-group-form-load-ships"
+					bind:value={loadShips}
+				/>
+			</label>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.cargo")}
+				<select
+					data-testid="inspector-ship-group-form-load-cargo"
+					bind:value={loadCargo}
+					disabled={group.cargo !== "NONE"}
+				>
+					{#each SHIP_GROUP_CARGO_VALUES as value (value)}
+						<option {value} disabled={planetStock[value] <= 0}>
+							{i18n.t(cargoLabelKey[value])}
+						</option>
+					{/each}
+				</select>
+			</label>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.quantity")}
+				<input
+					type="number"
+					min="0"
+					step="0.01"
+					data-testid="inspector-ship-group-form-load-quantity"
+					bind:value={loadQuantity}
+				/>
+			</label>
+			<div class="form-actions">
+				<button type="button" data-testid="inspector-ship-group-form-load-cancel" onclick={cancelForm}>
+					{i18n.t("game.inspector.ship_group.action.cancel")}
+				</button>
+				<button
+					type="submit"
+					class="primary"
+					data-testid="inspector-ship-group-form-load-confirm"
+					disabled={!(loadQuantity > 0)}
+				>
+					{i18n.t("game.inspector.ship_group.action.confirm")}
+				</button>
+			</div>
+		</form>
+	{/if}
+
+	{#if openForm === "unload"}
+		<form class="form" data-testid="inspector-ship-group-form-unload" onsubmit={(e) => { e.preventDefault(); void confirmUnload(); }}>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.ships", { max: String(maxShips()) })}
+				<input
+					type="number"
+					min="1"
+					max={String(group.count)}
+					step="1"
+					data-testid="inspector-ship-group-form-unload-ships"
+					bind:value={unloadShips}
+				/>
+			</label>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.quantity")}
+				<input
+					type="number"
+					min="0"
+					step="0.01"
+					data-testid="inspector-ship-group-form-unload-quantity"
+					bind:value={unloadQuantity}
+				/>
+			</label>
+			<div class="form-actions">
+				<button type="button" data-testid="inspector-ship-group-form-unload-cancel" onclick={cancelForm}>
+					{i18n.t("game.inspector.ship_group.action.cancel")}
+				</button>
+				<button
+					type="submit"
+					class="primary"
+					data-testid="inspector-ship-group-form-unload-confirm"
+					disabled={!(unloadQuantity > 0)}
+				>
+					{i18n.t("game.inspector.ship_group.action.confirm")}
+				</button>
+			</div>
+		</form>
+	{/if}
+
+	{#if openForm === "modernize"}
+		<form class="form" data-testid="inspector-ship-group-form-modernize" onsubmit={(e) => { e.preventDefault(); void confirmModernize(); }}>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.ships", { max: String(maxShips()) })}
+				<input
+					type="number"
+					min="1"
+					max={String(group.count)}
+					step="1"
+					data-testid="inspector-ship-group-form-modernize-ships"
+					bind:value={modernizeShips}
+				/>
+			</label>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.tech")}
+				<select
+					data-testid="inspector-ship-group-form-modernize-tech"
+					bind:value={modernizeTech}
+				>
+					{#each SHIP_GROUP_UPGRADE_TECH_VALUES as value (value)}
+						<option {value}>{i18n.t(techLabelKey[value])}</option>
+					{/each}
+				</select>
+			</label>
+			{#if modernizeTech !== "ALL"}
+				<label>
+					{i18n.t("game.inspector.ship_group.action.field.level")}
+					<input
+						type="number"
+						min="0"
+						step="0.01"
+						data-testid="inspector-ship-group-form-modernize-level"
+						bind:value={modernizeLevel}
+					/>
+				</label>
+			{/if}
+			<p class="preview" data-testid="inspector-ship-group-form-modernize-cost">
+				{#if modernizeCostPreview === null}
+					{i18n.t("game.inspector.ship_group.action.modernize.cost_unavailable")}
+				{:else}
+					{i18n.t("game.inspector.ship_group.action.modernize.cost", {
+						cost: formatNumber(modernizeCostPreview),
+					})}
+				{/if}
+			</p>
+			<div class="form-actions">
+				<button type="button" data-testid="inspector-ship-group-form-modernize-cancel" onclick={cancelForm}>
+					{i18n.t("game.inspector.ship_group.action.cancel")}
+				</button>
+				<button
+					type="submit"
+					class="primary"
+					data-testid="inspector-ship-group-form-modernize-confirm"
+					disabled={modernizeTech !== "ALL" && !(modernizeLevel > 0)}
+				>
+					{i18n.t("game.inspector.ship_group.action.confirm")}
+				</button>
+			</div>
+		</form>
+	{/if}
+
+	{#if openForm === "dismantle"}
+		<form class="form" data-testid="inspector-ship-group-form-dismantle" onsubmit={(e) => { e.preventDefault(); void confirmDismantle(); }}>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.ships", { max: String(maxShips()) })}
+				<input
+					type="number"
+					min="1"
+					max={String(group.count)}
+					step="1"
+					data-testid="inspector-ship-group-form-dismantle-ships"
+					bind:value={dismantleShips}
+				/>
+			</label>
+			{#if !ownPlanet && !uninhabitedPlanet && carryingColonists}
+				<p class="warning" data-testid="inspector-ship-group-form-dismantle-warning">
+					{i18n.t("game.inspector.ship_group.action.dismantle.warning")}
+				</p>
+			{/if}
+			<div class="form-actions">
+				<button type="button" data-testid="inspector-ship-group-form-dismantle-cancel" onclick={cancelForm}>
+					{i18n.t("game.inspector.ship_group.action.cancel")}
+				</button>
+				<button
+					type="submit"
+					class="primary"
+					data-testid="inspector-ship-group-form-dismantle-confirm"
+				>
+					{#if !ownPlanet && !uninhabitedPlanet && carryingColonists && !dismantleConfirmed}
+						{i18n.t("game.inspector.ship_group.action.confirm_destroy")}
+					{:else}
+						{i18n.t("game.inspector.ship_group.action.confirm")}
+					{/if}
+				</button>
+			</div>
+		</form>
+	{/if}
+
+	{#if openForm === "transfer"}
+		<form class="form" data-testid="inspector-ship-group-form-transfer" onsubmit={(e) => { e.preventDefault(); void confirmTransfer(); }}>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.ships", { max: String(maxShips()) })}
+				<input
+					type="number"
+					min="1"
+					max={String(group.count)}
+					step="1"
+					data-testid="inspector-ship-group-form-transfer-ships"
+					bind:value={transferShips}
+				/>
+			</label>
+			<label>
+				{i18n.t("game.inspector.ship_group.action.field.acceptor")}
+				<select
+					data-testid="inspector-ship-group-form-transfer-acceptor"
+					bind:value={transferAcceptor}
+				>
+					{#each otherRaces as race (race)}
+						<option value={race}>{race}</option>
+					{/each}
+				</select>
+			</label>
+			<div class="form-actions">
+				<button type="button" data-testid="inspector-ship-group-form-transfer-cancel" onclick={cancelForm}>
+					{i18n.t("game.inspector.ship_group.action.cancel")}
+				</button>
+				<button
+					type="submit"
+					class="primary"
+					data-testid="inspector-ship-group-form-transfer-confirm"
+					disabled={transferAcceptor === ""}
+				>
+					{i18n.t("game.inspector.ship_group.action.confirm")}
+				</button>
+			</div>
+		</form>
+	{/if}
+
+	{#if openForm === "joinFleet"}
+		<form class="form" data-testid="inspector-ship-group-form-join-fleet" onsubmit={(e) => { e.preventDefault(); void confirmJoinFleet(); }}>
+			{#if fleetsOnSamePlanet.length > 0}
+				<label>
+					<input
+						type="radio"
+						name="fleet-mode"
+						value="existing"
+						bind:group={joinFleetMode}
+						data-testid="inspector-ship-group-form-join-fleet-mode-existing"
+					/>
+					{i18n.t("game.inspector.ship_group.action.field.fleet")}
+				</label>
+				{#if joinFleetMode === "existing"}
+					<select
+						data-testid="inspector-ship-group-form-join-fleet-existing"
+						bind:value={joinFleetExisting}
+					>
+						{#each fleetsOnSamePlanet as fleet (fleet.name)}
+							<option value={fleet.name}>{fleet.name}</option>
+						{/each}
+					</select>
+				{/if}
+			{/if}
+			<label>
+				<input
+					type="radio"
+					name="fleet-mode"
+					value="new"
+					bind:group={joinFleetMode}
+					data-testid="inspector-ship-group-form-join-fleet-mode-new"
+				/>
+				{i18n.t("game.inspector.ship_group.action.fleet.create_new")}
+			</label>
+			{#if joinFleetMode === "new"}
+				<input
+					type="text"
+					data-testid="inspector-ship-group-form-join-fleet-new"
+					bind:value={joinFleetNew}
+					placeholder={i18n.t("game.inspector.ship_group.action.field.fleet")}
+				/>
+			{/if}
+			<div class="form-actions">
+				<button type="button" data-testid="inspector-ship-group-form-join-fleet-cancel" onclick={cancelForm}>
+					{i18n.t("game.inspector.ship_group.action.cancel")}
+				</button>
+				<button
+					type="submit"
+					class="primary"
+					data-testid="inspector-ship-group-form-join-fleet-confirm"
+					disabled={(joinFleetMode === "existing" ? joinFleetExisting : joinFleetNew) === ""}
+				>
+					{i18n.t("game.inspector.ship_group.action.confirm")}
+				</button>
+			</div>
+		</form>
+	{/if}
+
+	{#if disabledStateTooltip() !== null && openForm === null}
+		<p class="hint" data-testid="inspector-ship-group-actions-state-hint">
+			{disabledStateTooltip()}
+		</p>
+	{/if}
+</section>
+
+<style>
+	.actions {
+		display: flex;
+		flex-direction: column;
+		gap: 0.5rem;
+	}
+	.row {
+		display: flex;
+		flex-wrap: wrap;
+		gap: 0.35rem;
+	}
+	.action {
+		font: inherit;
+		font-size: 0.85rem;
+		padding: 0.2rem 0.55rem;
+		background: transparent;
+		color: #aab;
+		border: 1px solid #2a3150;
+		border-radius: 3px;
+		cursor: pointer;
+	}
+	.action:not(:disabled):hover {
+		color: #e8eaf6;
+		border-color: #6d8cff;
+	}
+	.action:disabled {
+		cursor: not-allowed;
+		opacity: 0.4;
+	}
+	.form {
+		display: flex;
+		flex-direction: column;
+		gap: 0.4rem;
+		padding: 0.5rem;
+		border: 1px solid #2a3150;
+		border-radius: 3px;
+		background: #0d1224;
+	}
+	.form label {
+		display: flex;
+		flex-direction: column;
+		gap: 0.2rem;
+		font-size: 0.85rem;
+		color: #aab;
+	}
+	.form input[type="number"],
+	.form input[type="text"],
+	.form select {
+		font: inherit;
+		padding: 0.25rem 0.4rem;
+		background: #0a0e1a;
+		color: #e8eaf6;
+		border: 1px solid #2a3150;
+		border-radius: 3px;
+	}
+	.form .destination-row {
+		display: flex;
+		flex-wrap: wrap;
+		align-items: center;
+		gap: 0.5rem;
+		font-size: 0.85rem;
+	}
+	.form .destination-row .label {
+		color: #aab;
+	}
+	.form-actions {
+		display: flex;
+		gap: 0.4rem;
+		margin-top: 0.25rem;
+	}
+	.form-actions button {
+		font: inherit;
+		font-size: 0.85rem;
+		padding: 0.25rem 0.65rem;
+		background: transparent;
+		color: #aab;
+		border: 1px solid #2a3150;
+		border-radius: 3px;
+		cursor: pointer;
+	}
+	.form-actions button.primary {
+		color: #e8eaf6;
+		border-color: #4f6dd9;
+	}
+	.form-actions button:disabled {
+		cursor: not-allowed;
+		opacity: 0.5;
+	}
+	.preview {
+		margin: 0;
+		font-size: 0.85rem;
+		color: #aab;
+	}
+	.warning {
+		margin: 0;
+		font-size: 0.85rem;
+		color: #d9a07a;
+	}
+	.hint {
+		margin: 0;
+		font-size: 0.8rem;
+		color: #888;
+	}
+</style>
diff --git a/ui/frontend/src/lib/sidebar/inspector-tab.svelte b/ui/frontend/src/lib/sidebar/inspector-tab.svelte
index 50be659..031f382 100644
--- a/ui/frontend/src/lib/sidebar/inspector-tab.svelte
+++ b/ui/frontend/src/lib/sidebar/inspector-tab.svelte
@@ -89,12 +89,23 @@ from the Phase 10 stub.
 	const localPlayerDrive = $derived(
 		renderedReport?.report?.localPlayerDrive ?? 0,
 	);
+	const localPlayerWeapons = $derived(
+		renderedReport?.report?.localPlayerWeapons ?? 0,
+	);
+	const localPlayerShields = $derived(
+		renderedReport?.report?.localPlayerShields ?? 0,
+	);
+	const localPlayerCargo = $derived(
+		renderedReport?.report?.localPlayerCargo ?? 0,
+	);
 	const localShipGroups = $derived(
 		renderedReport?.report?.localShipGroups ?? [],
 	);
 	const otherShipGroups = $derived(
 		renderedReport?.report?.otherShipGroups ?? [],
 	);
+	const localFleets = $derived(renderedReport?.report?.localFleets ?? []);
+	const otherRaces = $derived(renderedReport?.report?.otherRaces ?? []);
 	const localRace = $derived(renderedReport?.report?.race ?? "");
 </script>
 
@@ -113,7 +124,19 @@ from the Phase 10 stub.
 			{localRace}
 		/>
 	{:else if selectedShipGroup !== null}
-		<ShipGroup selection={selectedShipGroup} planets={allPlanets} />
+		<ShipGroup
+			selection={selectedShipGroup}
+			planets={allPlanets}
+			{localShipClass}
+			{localFleets}
+			{otherRaces}
+			{mapWidth}
+			{mapHeight}
+			{localPlayerDrive}
+			{localPlayerWeapons}
+			{localPlayerShields}
+			{localPlayerCargo}
+		/>
 	{:else}
 		<h3>{i18n.t("game.sidebar.tab.inspector")}</h3>
 		<p>{i18n.t("game.sidebar.empty.inspector")}</p>
diff --git a/ui/frontend/src/lib/sidebar/order-tab.svelte b/ui/frontend/src/lib/sidebar/order-tab.svelte
index 7442ba4..f2fa213 100644
--- a/ui/frontend/src/lib/sidebar/order-tab.svelte
+++ b/ui/frontend/src/lib/sidebar/order-tab.svelte
@@ -77,9 +77,57 @@ Tests exercise the tab through `__galaxyDebug.seedOrderDraft`
 				return i18n.t("game.sidebar.order.label.ship_class_remove", {
 					name: cmd.name,
 				});
+			case "breakShipGroup":
+				return i18n.t("game.sidebar.order.label.ship_group_break", {
+					group: shortGroupId(cmd.groupId),
+					quantity: String(cmd.quantity),
+				});
+			case "sendShipGroup":
+				return i18n.t("game.sidebar.order.label.ship_group_send", {
+					group: shortGroupId(cmd.groupId),
+					destination: String(cmd.destinationPlanetNumber),
+				});
+			case "loadShipGroup":
+				return i18n.t("game.sidebar.order.label.ship_group_load", {
+					group: shortGroupId(cmd.groupId),
+					cargo: cmd.cargo,
+					quantity: String(cmd.quantity),
+				});
+			case "unloadShipGroup":
+				return i18n.t("game.sidebar.order.label.ship_group_unload", {
+					group: shortGroupId(cmd.groupId),
+					quantity: String(cmd.quantity),
+				});
+			case "upgradeShipGroup":
+				return i18n.t("game.sidebar.order.label.ship_group_upgrade", {
+					group: shortGroupId(cmd.groupId),
+					tech: cmd.tech,
+					level: String(cmd.level),
+				});
+			case "dismantleShipGroup":
+				return i18n.t("game.sidebar.order.label.ship_group_dismantle", {
+					group: shortGroupId(cmd.groupId),
+				});
+			case "transferShipGroup":
+				return i18n.t("game.sidebar.order.label.ship_group_transfer", {
+					group: shortGroupId(cmd.groupId),
+					acceptor: cmd.acceptor,
+				});
+			case "joinFleetShipGroup":
+				return i18n.t("game.sidebar.order.label.ship_group_join_fleet", {
+					group: shortGroupId(cmd.groupId),
+					fleet: cmd.name,
+				});
 		}
 	}
 
+	// Short identifier for the order-tab so the human-readable label
+	// stays glanceable; the full UUID is still in the underlying
+	// command and visible in the inspector overlay.
+	function shortGroupId(uuid: string): string {
+		return uuid.length > 8 ? uuid.slice(0, 8) : uuid;
+	}
+
 	function statusOf(cmd: OrderCommand): CommandStatus {
 		return draft?.statuses[cmd.id] ?? "draft";
 	}
diff --git a/ui/frontend/src/platform/core/index.ts b/ui/frontend/src/platform/core/index.ts
index 669cacb..c604b5c 100644
--- a/ui/frontend/src/platform/core/index.ts
+++ b/ui/frontend/src/platform/core/index.ts
@@ -73,6 +73,12 @@ export interface CarryingMassInput {
 	cargoTech: number;
 }
 
+export interface BlockUpgradeCostInput {
+	blockMass: number;
+	currentTech: number;
+	targetTech: number;
+}
+
 export interface Core {
 	/**
 	 * signRequest returns the canonical signing input bytes for a v1
@@ -157,6 +163,17 @@ export interface Core {
 	 * cargoCapacity.
 	 */
 	carryingMass(input: CarryingMassInput): number;
+
+	/**
+	 * blockUpgradeCost wraps `pkg/calc/ship.go.BlockUpgradeCost`:
+	 * production cost of moving one ship block from currentTech to
+	 * targetTech, scaled by the block mass and a constant 10. Returns
+	 * 0 when blockMass is zero or targetTech is not above currentTech.
+	 * Phase 20's ship-group inspector calls this once per block
+	 * (drive, weapons, shields, cargo) to render the modernize cost
+	 * preview.
+	 */
+	blockUpgradeCost(input: BlockUpgradeCostInput): number;
 }
 
 export type CoreLoader = () => Promise<Core>;
diff --git a/ui/frontend/src/platform/core/wasm.ts b/ui/frontend/src/platform/core/wasm.ts
index ab88fc6..499bb26 100644
--- a/ui/frontend/src/platform/core/wasm.ts
+++ b/ui/frontend/src/platform/core/wasm.ts
@@ -9,6 +9,7 @@
 // served from `static/core.wasm`.
 
 import type {
+	BlockUpgradeCostInput,
 	CargoCapacityInput,
 	CarryingMassInput,
 	Core,
@@ -50,6 +51,7 @@ interface GalaxyCoreBridge {
 	speed(input: SpeedInput): number;
 	cargoCapacity(input: CargoCapacityInput): number;
 	carryingMass(input: CarryingMassInput): number;
+	blockUpgradeCost(input: BlockUpgradeCostInput): number;
 }
 
 interface BridgeRequestFields {
@@ -210,6 +212,9 @@ export function adaptBridge(bridge: GalaxyCoreBridge): Core {
 		carryingMass(input: CarryingMassInput): number {
 			return bridge.carryingMass(input);
 		},
+		blockUpgradeCost(input: BlockUpgradeCostInput): number {
+			return bridge.blockUpgradeCost(input);
+		},
 	};
 }
 
diff --git a/ui/frontend/src/routes/games/[id]/+layout.svelte b/ui/frontend/src/routes/games/[id]/+layout.svelte
index 1c84ef4..32cfe5e 100644
--- a/ui/frontend/src/routes/games/[id]/+layout.svelte
+++ b/ui/frontend/src/routes/games/[id]/+layout.svelte
@@ -180,12 +180,27 @@ fresh.
 	const inspectorLocalDrive = $derived(
 		renderedReport.report?.localPlayerDrive ?? 0,
 	);
+	const inspectorLocalWeapons = $derived(
+		renderedReport.report?.localPlayerWeapons ?? 0,
+	);
+	const inspectorLocalShields = $derived(
+		renderedReport.report?.localPlayerShields ?? 0,
+	);
+	const inspectorLocalCargo = $derived(
+		renderedReport.report?.localPlayerCargo ?? 0,
+	);
 	const inspectorLocalShipGroups = $derived(
 		renderedReport.report?.localShipGroups ?? [],
 	);
 	const inspectorOtherShipGroups = $derived(
 		renderedReport.report?.otherShipGroups ?? [],
 	);
+	const inspectorLocalFleets = $derived(
+		renderedReport.report?.localFleets ?? [],
+	);
+	const inspectorOtherRaces = $derived(
+		renderedReport.report?.otherRaces ?? [],
+	);
 	const inspectorLocalRace = $derived(renderedReport.report?.race ?? "");
 
 	// Reveal the inspector whenever a new planet selection lands.
@@ -340,6 +355,15 @@ fresh.
 	<ShipGroupSheet
 		selection={selectedShipGroup}
 		planets={inspectorPlanets}
+		{localShipClass}
+		localFleets={inspectorLocalFleets}
+		otherRaces={inspectorOtherRaces}
+		mapWidth={inspectorMapWidth}
+		mapHeight={inspectorMapHeight}
+		localPlayerDrive={inspectorLocalDrive}
+		localPlayerWeapons={inspectorLocalWeapons}
+		localPlayerShields={inspectorLocalShields}
+		localPlayerCargo={inspectorLocalCargo}
 		onMap={effectiveTool === "map"}
 		onClose={() => selection.clear()}
 	/>
diff --git a/ui/frontend/src/sync/order-draft.svelte.ts b/ui/frontend/src/sync/order-draft.svelte.ts
index c9aa874..5f81bb1 100644
--- a/ui/frontend/src/sync/order-draft.svelte.ts
+++ b/ui/frontend/src/sync/order-draft.svelte.ts
@@ -24,7 +24,12 @@
 import type { Cache } from "../platform/store/index";
 import type { GalaxyClient } from "../api/galaxy-client";
 import { fetchOrder } from "./order-load";
-import type { CommandStatus, OrderCommand } from "./order-types";
+import {
+	isShipGroupCargo,
+	isShipGroupUpgradeTech,
+	type CommandStatus,
+	type OrderCommand,
+} from "./order-types";
 import { submitOrder } from "./submit";
 import { validateEntityName } from "$lib/util/entity-name";
 import { validateShipClass } from "$lib/util/ship-class-validation";
@@ -513,6 +518,68 @@ function validateCommand(cmd: OrderCommand): CommandStatus {
 			// active production / ship groups. Local validation only
 			// guards the name shape.
 			return validateEntityName(cmd.name).ok ? "valid" : "invalid";
+		case "breakShipGroup":
+			// Engine rule (`controller/ship_group.go.breakGroup`):
+			// quantity must be at least 1 and strictly less than the
+			// source group size. We do not know the source size here
+			// (it lives on the report), so the inspector enforces the
+			// upper bound before emitting; locally we only refuse the
+			// degenerate cases — non-positive `quantity`, missing or
+			// equal UUIDs.
+			if (cmd.quantity <= 0) return "invalid";
+			if (!isUuid(cmd.groupId) || !isUuid(cmd.newGroupId)) return "invalid";
+			if (cmd.groupId === cmd.newGroupId) return "invalid";
+			return "valid";
+		case "sendShipGroup":
+			// Reach is enforced by the picker before the command lands
+			// in the draft. Locally we only refuse a degenerate
+			// destination (the engine uses planet number `0` as the
+			// "no planet" sentinel; FBS encodes as `int64`, so any
+			// strictly-positive number is wire-valid).
+			if (cmd.destinationPlanetNumber <= 0) return "invalid";
+			if (!isUuid(cmd.groupId)) return "invalid";
+			return "valid";
+		case "loadShipGroup":
+			// Cargo type and quantity are pre-checked by the inspector
+			// against the planet stock and the group's free capacity;
+			// local validation only guards the wire-valid shape.
+			if (!isShipGroupCargo(cmd.cargo)) return "invalid";
+			if (cmd.quantity <= 0) return "invalid";
+			if (!isUuid(cmd.groupId)) return "invalid";
+			return "valid";
+		case "unloadShipGroup":
+			if (cmd.quantity <= 0) return "invalid";
+			if (!isUuid(cmd.groupId)) return "invalid";
+			return "valid";
+		case "upgradeShipGroup":
+			// Engine rule
+			// (`controller/ship_group_upgrade.go.shipGroupUpgrade:56`):
+			// `tech === "ALL"` requires `level === 0`; per-block tech
+			// requires a strictly positive level. The inspector also
+			// caps the level to the player's race tech, but the
+			// engine re-validates server-side.
+			if (!isShipGroupUpgradeTech(cmd.tech)) return "invalid";
+			if (cmd.tech === "ALL") {
+				if (cmd.level !== 0) return "invalid";
+			} else if (cmd.level <= 0) {
+				return "invalid";
+			}
+			if (!isUuid(cmd.groupId)) return "invalid";
+			return "valid";
+		case "dismantleShipGroup":
+			return isUuid(cmd.groupId) ? "valid" : "invalid";
+		case "transferShipGroup":
+			// `acceptor` is a race name; race names follow the same
+			// entity-name rules as planet/fleet names. The inspector
+			// restricts the picker to `GameReport.otherRaces`, so a
+			// locally-valid name is always a real race.
+			if (!validateEntityName(cmd.acceptor).ok) return "invalid";
+			if (!isUuid(cmd.groupId)) return "invalid";
+			return "valid";
+		case "joinFleetShipGroup":
+			if (!validateEntityName(cmd.name).ok) return "invalid";
+			if (!isUuid(cmd.groupId)) return "invalid";
+			return "valid";
 		case "placeholder":
 			// Phase 12 placeholder entries are content-free and never
 			// transition out of `draft` — they are not submittable.
diff --git a/ui/frontend/src/sync/order-load.ts b/ui/frontend/src/sync/order-load.ts
index 067d428..b258d29 100644
--- a/ui/frontend/src/sync/order-load.ts
+++ b/ui/frontend/src/sync/order-load.ts
@@ -18,8 +18,18 @@ import {
 	CommandPlanetRouteSet,
 	CommandShipClassCreate,
 	CommandShipClassRemove,
+	CommandShipGroupBreak,
+	CommandShipGroupDismantle,
+	CommandShipGroupJoinFleet,
+	CommandShipGroupLoad,
+	CommandShipGroupSend,
+	CommandShipGroupTransfer,
+	CommandShipGroupUnload,
+	CommandShipGroupUpgrade,
 	PlanetProduction,
 	PlanetRouteLoadType,
+	ShipGroupCargo,
+	ShipGroupUpgradeTech,
 	UserGamesOrderGet,
 	UserGamesOrderGetResponse,
 } from "../proto/galaxy/fbs/order";
@@ -27,6 +37,8 @@ import type {
 	CargoLoadType,
 	OrderCommand,
 	ProductionType,
+	ShipGroupCargo as ShipGroupCargoLiteral,
+	ShipGroupUpgradeTech as ShipGroupUpgradeTechLiteral,
 } from "./order-types";
 
 const MESSAGE_TYPE = "user.games.order.get";
@@ -222,6 +234,102 @@ function decodeCommand(item: CommandItemView): OrderCommand | null {
 				name: inner.name() ?? "",
 			};
 		}
+		case CommandPayload.CommandShipGroupBreak: {
+			const inner = new CommandShipGroupBreak();
+			item.payload(inner);
+			return {
+				kind: "breakShipGroup",
+				id,
+				groupId: inner.id() ?? "",
+				newGroupId: inner.newId() ?? "",
+				quantity: Number(inner.quantity()),
+			};
+		}
+		case CommandPayload.CommandShipGroupSend: {
+			const inner = new CommandShipGroupSend();
+			item.payload(inner);
+			return {
+				kind: "sendShipGroup",
+				id,
+				groupId: inner.id() ?? "",
+				destinationPlanetNumber: Number(inner.destination()),
+			};
+		}
+		case CommandPayload.CommandShipGroupLoad: {
+			const inner = new CommandShipGroupLoad();
+			item.payload(inner);
+			const cargo = shipGroupCargoFromFBS(inner.cargo());
+			if (cargo === null) {
+				console.warn(
+					`fetchOrder: skipping CommandShipGroupLoad with unknown cargo enum (${inner.cargo()})`,
+				);
+				return null;
+			}
+			return {
+				kind: "loadShipGroup",
+				id,
+				groupId: inner.id() ?? "",
+				cargo,
+				quantity: inner.quantity(),
+			};
+		}
+		case CommandPayload.CommandShipGroupUnload: {
+			const inner = new CommandShipGroupUnload();
+			item.payload(inner);
+			return {
+				kind: "unloadShipGroup",
+				id,
+				groupId: inner.id() ?? "",
+				quantity: inner.quantity(),
+			};
+		}
+		case CommandPayload.CommandShipGroupUpgrade: {
+			const inner = new CommandShipGroupUpgrade();
+			item.payload(inner);
+			const tech = shipGroupUpgradeTechFromFBS(inner.tech());
+			if (tech === null) {
+				console.warn(
+					`fetchOrder: skipping CommandShipGroupUpgrade with unknown tech enum (${inner.tech()})`,
+				);
+				return null;
+			}
+			return {
+				kind: "upgradeShipGroup",
+				id,
+				groupId: inner.id() ?? "",
+				tech,
+				level: inner.level(),
+			};
+		}
+		case CommandPayload.CommandShipGroupDismantle: {
+			const inner = new CommandShipGroupDismantle();
+			item.payload(inner);
+			return {
+				kind: "dismantleShipGroup",
+				id,
+				groupId: inner.id() ?? "",
+			};
+		}
+		case CommandPayload.CommandShipGroupTransfer: {
+			const inner = new CommandShipGroupTransfer();
+			item.payload(inner);
+			return {
+				kind: "transferShipGroup",
+				id,
+				groupId: inner.id() ?? "",
+				acceptor: inner.acceptor() ?? "",
+			};
+		}
+		case CommandPayload.CommandShipGroupJoinFleet: {
+			const inner = new CommandShipGroupJoinFleet();
+			item.payload(inner);
+			return {
+				kind: "joinFleetShipGroup",
+				id,
+				groupId: inner.id() ?? "",
+				name: inner.name() ?? "",
+			};
+		}
 		default:
 			console.warn(
 				`fetchOrder: skipping unknown command kind (payloadType=${payloadType})`,
@@ -288,6 +396,55 @@ export function cargoLoadTypeFromFBS(
 	}
 }
 
+/**
+ * shipGroupCargoFromFBS reverses `shipGroupCargoToFBS` from
+ * `submit.ts`. `ShipGroupCargo.UNKNOWN` and any out-of-band value
+ * yield `null` so the caller drops the entry rather than
+ * fabricating a synthetic cargo type.
+ */
+export function shipGroupCargoFromFBS(
+	value: ShipGroupCargo,
+): ShipGroupCargoLiteral | null {
+	switch (value) {
+		case ShipGroupCargo.COL:
+			return "COL";
+		case ShipGroupCargo.CAP:
+			return "CAP";
+		case ShipGroupCargo.MAT:
+			return "MAT";
+		case ShipGroupCargo.UNKNOWN:
+			return null;
+		default:
+			return null;
+	}
+}
+
+/**
+ * shipGroupUpgradeTechFromFBS reverses `shipGroupUpgradeTechToFBS`
+ * from `submit.ts`. `ShipGroupUpgradeTech.UNKNOWN` and any
+ * out-of-band value yield `null`.
+ */
+export function shipGroupUpgradeTechFromFBS(
+	value: ShipGroupUpgradeTech,
+): ShipGroupUpgradeTechLiteral | null {
+	switch (value) {
+		case ShipGroupUpgradeTech.ALL:
+			return "ALL";
+		case ShipGroupUpgradeTech.DRIVE:
+			return "DRIVE";
+		case ShipGroupUpgradeTech.WEAPONS:
+			return "WEAPONS";
+		case ShipGroupUpgradeTech.SHIELDS:
+			return "SHIELDS";
+		case ShipGroupUpgradeTech.CARGO:
+			return "CARGO";
+		case ShipGroupUpgradeTech.UNKNOWN:
+			return null;
+		default:
+			return null;
+	}
+}
+
 function decodeError(
 	payload: Uint8Array,
 	resultCode: string,
diff --git a/ui/frontend/src/sync/order-types.ts b/ui/frontend/src/sync/order-types.ts
index 2086a29..7fdc37d 100644
--- a/ui/frontend/src/sync/order-types.ts
+++ b/ui/frontend/src/sync/order-types.ts
@@ -166,6 +166,209 @@ export interface RemoveShipClassCommand {
 	readonly name: string;
 }
 
+/**
+ * ShipGroupCargo mirrors the engine `ShipGroupCargo` enum
+ * (`pkg/schema/fbs/order.fbs`). Three values: colonists, capital
+ * (industry crates), and materials. Empty (`EMP`) is a route-level
+ * concept (`PlanetRouteLoadType`) and is not a valid cargo type for a
+ * ship-group load command — the FBS enum deliberately omits it.
+ */
+export type ShipGroupCargo = "COL" | "CAP" | "MAT";
+
+/**
+ * SHIP_GROUP_CARGO_VALUES is the canonical tuple of `ShipGroupCargo`
+ * literals. Used by validators and the FBS converters in
+ * `submit.ts` and `order-load.ts` to narrow incoming strings.
+ */
+export const SHIP_GROUP_CARGO_VALUES = [
+	"COL",
+	"CAP",
+	"MAT",
+] as const satisfies readonly ShipGroupCargo[];
+
+/**
+ * isShipGroupCargo narrows an arbitrary string to the
+ * `ShipGroupCargo` union.
+ */
+export function isShipGroupCargo(value: string): value is ShipGroupCargo {
+	return (SHIP_GROUP_CARGO_VALUES as readonly string[]).includes(value);
+}
+
+/**
+ * ShipGroupUpgradeTech mirrors the engine `ShipGroupUpgradeTech`
+ * enum (`pkg/schema/fbs/order.fbs`): `ALL` upgrades every applicable
+ * block to the player's current race tech (level argument must be 0
+ * — see `controller/ship_group_upgrade.go:56`); the four per-block
+ * values upgrade exactly that block to the requested level.
+ */
+export type ShipGroupUpgradeTech =
+	| "ALL"
+	| "DRIVE"
+	| "WEAPONS"
+	| "SHIELDS"
+	| "CARGO";
+
+/**
+ * SHIP_GROUP_UPGRADE_TECH_VALUES is the canonical tuple of
+ * `ShipGroupUpgradeTech` literals. The order matches the FBS enum.
+ */
+export const SHIP_GROUP_UPGRADE_TECH_VALUES = [
+	"ALL",
+	"DRIVE",
+	"WEAPONS",
+	"SHIELDS",
+	"CARGO",
+] as const satisfies readonly ShipGroupUpgradeTech[];
+
+/**
+ * isShipGroupUpgradeTech narrows an arbitrary string to the
+ * `ShipGroupUpgradeTech` union.
+ */
+export function isShipGroupUpgradeTech(
+	value: string,
+): value is ShipGroupUpgradeTech {
+	return (SHIP_GROUP_UPGRADE_TECH_VALUES as readonly string[]).includes(value);
+}
+
+/**
+ * BreakShipGroupCommand splits a player-owned ship group into two:
+ * the original keeps `originalCount - quantity` ships and a new group
+ * with `newGroupId` carries `quantity`. Used both as a stand-alone
+ * action and as the implicit prelude to Send / Load / Unload /
+ * Modernize / Dismantle / Transfer when the player picks fewer than
+ * all ships. Engine rules (`controller/ship_group.go.breakGroup`):
+ * source group must be `StateInOrbit`, `quantity` must be in `[1,
+ * originalCount - 1]` for a real split. The new group carries a
+ * proportional slice of the cargo and starts unattached to any fleet.
+ */
+export interface BreakShipGroupCommand {
+	readonly kind: "breakShipGroup";
+	readonly id: string;
+	readonly groupId: string;
+	readonly newGroupId: string;
+	readonly quantity: number;
+}
+
+/**
+ * SendShipGroupCommand launches a player-owned ship group toward a
+ * destination planet. Engine rules
+ * (`controller/ship_group_send.go.shipGroupSend`): group must be
+ * `StateInOrbit`; ship class must have a non-zero drive block; the
+ * destination must be within the player's current
+ * `FlightDistance() = localPlayerDrive * 40` (torus-aware).
+ * The picker filters the planet list before emitting, so a draft
+ * entry that survives validation is always reachable at submit time.
+ */
+export interface SendShipGroupCommand {
+	readonly kind: "sendShipGroup";
+	readonly id: string;
+	readonly groupId: string;
+	readonly destinationPlanetNumber: number;
+}
+
+/**
+ * LoadShipGroupCommand loads cargo of one of the three ship-group
+ * cargo types onto a player-owned group. Engine rules
+ * (`controller/ship_group.go.shipGroupLoad`): group must be
+ * `StateInOrbit`; planet must be owned by the player or unowned;
+ * ship class must have a non-zero cargo block; the existing cargo
+ * type (if any) must equal `cargo`; `quantity` is bounded by the
+ * planet's stock and the group's free capacity. The inspector
+ * pre-checks each of these so a draft entry is always wire-valid.
+ */
+export interface LoadShipGroupCommand {
+	readonly kind: "loadShipGroup";
+	readonly id: string;
+	readonly groupId: string;
+	readonly cargo: ShipGroupCargo;
+	readonly quantity: number;
+}
+
+/**
+ * UnloadShipGroupCommand drops cargo from a player-owned group at
+ * its current orbit. Engine rules
+ * (`controller/ship_group.go.shipGroupUnload`): group must be
+ * `StateInOrbit`; ship class must have a non-zero cargo block; group
+ * must currently carry cargo. Colonists (`COL`) cannot be unloaded
+ * over a foreign planet — the inspector disables the action with a
+ * tooltip in that case. The cargo type is implicit (whatever the
+ * group is carrying); only `quantity` is sent on the wire.
+ */
+export interface UnloadShipGroupCommand {
+	readonly kind: "unloadShipGroup";
+	readonly id: string;
+	readonly groupId: string;
+	readonly quantity: number;
+}
+
+/**
+ * UpgradeShipGroupCommand schedules a tech upgrade for a player-
+ * owned group at its current orbit. Engine rules
+ * (`controller/ship_group_upgrade.go.shipGroupUpgrade`): group must
+ * be `StateInOrbit`; the planet must be owned by the player or
+ * unowned; for per-block techs the requested `level` must be in
+ * `(group.tech, race.tech]`; for `tech === "ALL"` the `level` must
+ * be 0 (the engine fans the upgrade out to every block whose mass is
+ * non-zero). The inspector renders a live cost preview through
+ * `core.blockUpgradeCost` to make the production cost visible before
+ * the player commits.
+ */
+export interface UpgradeShipGroupCommand {
+	readonly kind: "upgradeShipGroup";
+	readonly id: string;
+	readonly groupId: string;
+	readonly tech: ShipGroupUpgradeTech;
+	readonly level: number;
+}
+
+/**
+ * DismantleShipGroupCommand deconstructs a player-owned group at its
+ * current orbit, returning the empty mass to the planet's materials
+ * stockpile. Engine rules (`controller/ship_group.go.shipGroupDismantle`):
+ * group must be `StateInOrbit`; over a foreign planet, colonists
+ * (`COL`) on board are *lost* — the inspector surfaces an explicit
+ * two-step confirmation in that case before adding the command to
+ * the draft.
+ */
+export interface DismantleShipGroupCommand {
+	readonly kind: "dismantleShipGroup";
+	readonly id: string;
+	readonly groupId: string;
+}
+
+/**
+ * TransferShipGroupCommand hands a player-owned group to another
+ * race. Engine rules (`controller/ship_group.go.shipGroupTransfer`):
+ * acceptor must be a different, non-extinct race; group must not
+ * already be in `StateTransfer`. The inspector restricts the
+ * acceptor picker to `GameReport.otherRaces` (non-extinct ≠ self),
+ * so a draft entry always names a real race.
+ */
+export interface TransferShipGroupCommand {
+	readonly kind: "transferShipGroup";
+	readonly id: string;
+	readonly groupId: string;
+	readonly acceptor: string;
+}
+
+/**
+ * JoinFleetShipGroupCommand attaches a player-owned group to a fleet
+ * (creating it on the fly if no fleet by that name exists). Engine
+ * rules (`controller/fleet.go.ShipGroupJoinFleet`): group must be
+ * `StateInOrbit`; the target fleet, when it already exists, must
+ * sit in the same orbit as the group; `name` must pass
+ * `validateEntityName`. Because the engine handles the whole-group
+ * attach atomically (no per-ship counter), this command does not
+ * support implicit-split — the inspector exposes Split as a
+ * separate explicit action when partial detachment is desired.
+ */
+export interface JoinFleetShipGroupCommand {
+	readonly kind: "joinFleetShipGroup";
+	readonly id: string;
+	readonly groupId: string;
+	readonly name: string;
+}
+
 /**
  * OrderCommand is the discriminated union of every command shape the
  * local order draft can hold. The `kind` field is the discriminator;
@@ -179,7 +382,15 @@ export type OrderCommand =
 	| SetCargoRouteCommand
 	| RemoveCargoRouteCommand
 	| CreateShipClassCommand
-	| RemoveShipClassCommand;
+	| RemoveShipClassCommand
+	| BreakShipGroupCommand
+	| SendShipGroupCommand
+	| LoadShipGroupCommand
+	| UnloadShipGroupCommand
+	| UpgradeShipGroupCommand
+	| DismantleShipGroupCommand
+	| TransferShipGroupCommand
+	| JoinFleetShipGroupCommand;
 
 /**
  * PRODUCTION_TYPE_VALUES is the canonical tuple of `ProductionType`
diff --git a/ui/frontend/src/sync/submit.ts b/ui/frontend/src/sync/submit.ts
index d402cb6..9e46e21 100644
--- a/ui/frontend/src/sync/submit.ts
+++ b/ui/frontend/src/sync/submit.ts
@@ -33,8 +33,18 @@ import {
 	CommandPlanetRouteSet,
 	CommandShipClassCreate,
 	CommandShipClassRemove,
+	CommandShipGroupBreak,
+	CommandShipGroupDismantle,
+	CommandShipGroupJoinFleet,
+	CommandShipGroupLoad,
+	CommandShipGroupSend,
+	CommandShipGroupTransfer,
+	CommandShipGroupUnload,
+	CommandShipGroupUpgrade,
 	PlanetProduction,
 	PlanetRouteLoadType,
+	ShipGroupCargo,
+	ShipGroupUpgradeTech,
 	UserGamesOrder,
 	UserGamesOrderResponse,
 } from "../proto/galaxy/fbs/order";
@@ -42,6 +52,8 @@ import type {
 	CargoLoadType,
 	OrderCommand,
 	ProductionType,
+	ShipGroupCargo as ShipGroupCargoLiteral,
+	ShipGroupUpgradeTech as ShipGroupUpgradeTechLiteral,
 } from "./order-types";
 
 const MESSAGE_TYPE = "user.games.order";
@@ -222,6 +234,109 @@ function encodeCommandPayload(
 				payloadOffset: offset,
 			};
 		}
+		case "breakShipGroup": {
+			const idOffset = builder.createString(cmd.groupId);
+			const newIdOffset = builder.createString(cmd.newGroupId);
+			CommandShipGroupBreak.startCommandShipGroupBreak(builder);
+			CommandShipGroupBreak.addId(builder, idOffset);
+			CommandShipGroupBreak.addNewId(builder, newIdOffset);
+			CommandShipGroupBreak.addQuantity(builder, BigInt(cmd.quantity));
+			const offset = CommandShipGroupBreak.endCommandShipGroupBreak(builder);
+			return {
+				payloadType: CommandPayload.CommandShipGroupBreak,
+				payloadOffset: offset,
+			};
+		}
+		case "sendShipGroup": {
+			const idOffset = builder.createString(cmd.groupId);
+			const offset = CommandShipGroupSend.createCommandShipGroupSend(
+				builder,
+				idOffset,
+				BigInt(cmd.destinationPlanetNumber),
+			);
+			return {
+				payloadType: CommandPayload.CommandShipGroupSend,
+				payloadOffset: offset,
+			};
+		}
+		case "loadShipGroup": {
+			const idOffset = builder.createString(cmd.groupId);
+			CommandShipGroupLoad.startCommandShipGroupLoad(builder);
+			CommandShipGroupLoad.addId(builder, idOffset);
+			CommandShipGroupLoad.addCargo(builder, shipGroupCargoToFBS(cmd.cargo));
+			CommandShipGroupLoad.addQuantity(builder, cmd.quantity);
+			const offset = CommandShipGroupLoad.endCommandShipGroupLoad(builder);
+			return {
+				payloadType: CommandPayload.CommandShipGroupLoad,
+				payloadOffset: offset,
+			};
+		}
+		case "unloadShipGroup": {
+			const idOffset = builder.createString(cmd.groupId);
+			const offset = CommandShipGroupUnload.createCommandShipGroupUnload(
+				builder,
+				idOffset,
+				cmd.quantity,
+			);
+			return {
+				payloadType: CommandPayload.CommandShipGroupUnload,
+				payloadOffset: offset,
+			};
+		}
+		case "upgradeShipGroup": {
+			const idOffset = builder.createString(cmd.groupId);
+			CommandShipGroupUpgrade.startCommandShipGroupUpgrade(builder);
+			CommandShipGroupUpgrade.addId(builder, idOffset);
+			CommandShipGroupUpgrade.addTech(
+				builder,
+				shipGroupUpgradeTechToFBS(cmd.tech),
+			);
+			CommandShipGroupUpgrade.addLevel(builder, cmd.level);
+			const offset = CommandShipGroupUpgrade.endCommandShipGroupUpgrade(builder);
+			return {
+				payloadType: CommandPayload.CommandShipGroupUpgrade,
+				payloadOffset: offset,
+			};
+		}
+		case "dismantleShipGroup": {
+			const idOffset = builder.createString(cmd.groupId);
+			const offset =
+				CommandShipGroupDismantle.createCommandShipGroupDismantle(
+					builder,
+					idOffset,
+				);
+			return {
+				payloadType: CommandPayload.CommandShipGroupDismantle,
+				payloadOffset: offset,
+			};
+		}
+		case "transferShipGroup": {
+			const idOffset = builder.createString(cmd.groupId);
+			const acceptorOffset = builder.createString(cmd.acceptor);
+			const offset = CommandShipGroupTransfer.createCommandShipGroupTransfer(
+				builder,
+				idOffset,
+				acceptorOffset,
+			);
+			return {
+				payloadType: CommandPayload.CommandShipGroupTransfer,
+				payloadOffset: offset,
+			};
+		}
+		case "joinFleetShipGroup": {
+			const idOffset = builder.createString(cmd.groupId);
+			const nameOffset = builder.createString(cmd.name);
+			const offset =
+				CommandShipGroupJoinFleet.createCommandShipGroupJoinFleet(
+					builder,
+					idOffset,
+					nameOffset,
+				);
+			return {
+				payloadType: CommandPayload.CommandShipGroupJoinFleet,
+				payloadOffset: offset,
+			};
+		}
 		case "placeholder":
 			throw new SubmitError(
 				"invalid_request",
@@ -277,6 +392,49 @@ export function cargoLoadTypeToFBS(value: CargoLoadType): PlanetRouteLoadType {
 	}
 }
 
+/**
+ * shipGroupCargoToFBS converts the wire-stable `ShipGroupCargo`
+ * literal to the FlatBuffers enum value. Mirrors the engine
+ * `ShipGroupCargo` enum (`pkg/schema/fbs/order.fbs`). The FBS enum
+ * carries an `UNKNOWN` zero value as the default; the encoder always
+ * emits one of the three real values.
+ */
+export function shipGroupCargoToFBS(
+	value: ShipGroupCargoLiteral,
+): ShipGroupCargo {
+	switch (value) {
+		case "COL":
+			return ShipGroupCargo.COL;
+		case "CAP":
+			return ShipGroupCargo.CAP;
+		case "MAT":
+			return ShipGroupCargo.MAT;
+	}
+}
+
+/**
+ * shipGroupUpgradeTechToFBS converts the wire-stable
+ * `ShipGroupUpgradeTech` literal to the FlatBuffers enum value.
+ * Mirrors the engine `ShipGroupUpgradeTech` enum
+ * (`pkg/schema/fbs/order.fbs`).
+ */
+export function shipGroupUpgradeTechToFBS(
+	value: ShipGroupUpgradeTechLiteral,
+): ShipGroupUpgradeTech {
+	switch (value) {
+		case "ALL":
+			return ShipGroupUpgradeTech.ALL;
+		case "DRIVE":
+			return ShipGroupUpgradeTech.DRIVE;
+		case "WEAPONS":
+			return ShipGroupUpgradeTech.WEAPONS;
+		case "SHIELDS":
+			return ShipGroupUpgradeTech.SHIELDS;
+		case "CARGO":
+			return ShipGroupUpgradeTech.CARGO;
+	}
+}
+
 function decodeOrderResponse(
 	payload: Uint8Array,
 	commands: OrderCommand[],
diff --git a/ui/frontend/static/core.wasm b/ui/frontend/static/core.wasm
index 0755a91..95ed1a1 100644
Binary files a/ui/frontend/static/core.wasm and b/ui/frontend/static/core.wasm differ
diff --git a/ui/frontend/tests/e2e/ship-group-send.spec.ts b/ui/frontend/tests/e2e/ship-group-send.spec.ts
new file mode 100644
index 0000000..bd21af7
--- /dev/null
+++ b/ui/frontend/tests/e2e/ship-group-send.spec.ts
@@ -0,0 +1,254 @@
+// Phase 20 end-to-end coverage for the ship-group Send action.
+// Loads a synthetic report with a local group of three Frontier
+// ships in orbit over Earth and a reachable destination planet
+// (Mars), opens the inspector by clicking the rendered group,
+// drives the Send form (asking for 2 ships out of 3), picks Mars
+// through the map-pick service, and asserts the resulting order
+// draft has both an implicit `breakShipGroup` and the targeted
+// `sendShipGroup` whose `groupId` references the freshly minted
+// sub-group ID. The synthetic flow uses a non-UUID game id, so
+// the auto-sync pipeline skips the network — the assertion
+// targets the in-memory draft via the order-tab UI.
+
+import { expect, test, type Page } from "@playwright/test";
+
+const SESSION_ID = "phase-20-send-session";
+
+interface DebugSurface {
+	ready?: boolean;
+	loadSession(): Promise<unknown>;
+	clearSession?(): Promise<void>;
+	setDeviceSessionId(id: string): Promise<void>;
+}
+
+declare global {
+	interface Window {
+		__galaxyDebug?: DebugSurface;
+	}
+}
+
+const SYNTHETIC_FIXTURE = {
+	turn: 1,
+	mapWidth: 200,
+	mapHeight: 200,
+	mapPlanets: 2,
+	race: "Earthlings",
+	player: [
+		{
+			name: "Earthlings",
+			drive: 5,
+			weapons: 0,
+			shields: 0,
+			cargo: 1,
+			population: 1000,
+			industry: 1000,
+			planets: 1,
+			relation: "-",
+			votes: 0,
+			extinct: false,
+		},
+		{
+			name: "Aliens",
+			drive: 4,
+			weapons: 2,
+			shields: 1,
+			cargo: 1,
+			population: 800,
+			industry: 800,
+			planets: 1,
+			relation: "-",
+			votes: 0,
+			extinct: false,
+		},
+	],
+	localPlanet: [
+		{
+			number: 1,
+			name: "Earth",
+			x: 100,
+			y: 100,
+			size: 1000,
+			population: 1000,
+			industry: 1000,
+			resources: 10,
+			production: "Capital",
+			capital: 0,
+			material: 0,
+			colonists: 100,
+			freeIndustry: 1000,
+		},
+	],
+	otherPlanet: [
+		{
+			number: 2,
+			name: "Mars",
+			x: 110,
+			y: 100,
+			size: 800,
+			population: 800,
+			industry: 800,
+			resources: 8,
+			production: "Capital",
+			capital: 0,
+			material: 0,
+			colonists: 80,
+			freeIndustry: 800,
+			owner: "Aliens",
+		},
+	],
+	uninhabitedPlanet: [],
+	unidentifiedPlanet: [],
+	localShipClass: [
+		{
+			name: "Frontier",
+			drive: 5,
+			armament: 0,
+			weapons: 0,
+			shields: 0,
+			cargo: 1,
+			mass: 12,
+		},
+	],
+	localGroup: [
+		{
+			id: "11111111-2222-3333-4444-555555555555",
+			number: 3,
+			class: "Frontier",
+			tech: { drive: 5, weapons: 0, shields: 0, cargo: 1 },
+			cargo: "-",
+			load: 0,
+			destination: 1,
+			speed: 25,
+			mass: 12,
+			state: "In_Orbit",
+		},
+	],
+	otherGroup: [],
+	incomingGroup: [],
+	unidentifiedGroup: [],
+	localFleet: [],
+};
+
+async function bootSession(page: Page): Promise<void> {
+	await page.goto("/__debug/store");
+	await expect(page.getByTestId("debug-store-ready")).toBeVisible();
+	await page.waitForFunction(
+		() => window.__galaxyDebug?.ready === true,
+	);
+	await page.evaluate(async () => {
+		const debug = window.__galaxyDebug!;
+		await debug.loadSession();
+		await debug.setDeviceSessionId("phase-20-send-session");
+	});
+	void SESSION_ID;
+}
+
+async function loadSyntheticGame(page: Page): Promise<void> {
+	await page.goto("/lobby");
+	await expect(page.getByTestId("lobby-synthetic-section")).toBeVisible();
+	const file = page.getByTestId("lobby-synthetic-file");
+	await file.setInputFiles({
+		name: "phase20.json",
+		mimeType: "application/json",
+		buffer: Buffer.from(JSON.stringify(SYNTHETIC_FIXTURE)),
+	});
+	await page.waitForURL(/\/games\/synthetic-[^/]+\/map$/, {
+		timeout: 10_000,
+	});
+	await expect(page.getByTestId("active-view-map")).toHaveAttribute(
+		"data-status",
+		"ready",
+	);
+}
+
+// projectWorldToScreen returns the pixel coordinates of a world-space
+// point (x, y) relative to the document, using the renderer's
+// debug-surface camera snapshot. Waits for the renderer to register
+// its debug providers (the in-game shell calls
+// `installRendererDebugSurface` on mount, then the providers attach
+// when `mountRenderer` resolves) so the spec is robust against the
+// async Pixi boot.
+async function projectWorldToScreen(
+	page: Page,
+	x: number,
+	y: number,
+): Promise<{ x: number; y: number }> {
+	await page.waitForFunction(() => {
+		const dbg = window.__galaxyDebug as unknown as
+			| { getMapCamera(): unknown }
+			| undefined;
+		if (dbg === undefined) return false;
+		return dbg.getMapCamera() !== null;
+	});
+	return page.evaluate(({ wx, wy }) => {
+		const debug = window.__galaxyDebug as unknown as {
+			getMapCamera(): {
+				camera: { centerX: number; centerY: number; scale: number };
+				viewport: { widthPx: number; heightPx: number };
+				canvasOrigin: { x: number; y: number };
+			} | null;
+		};
+		const cam = debug.getMapCamera();
+		if (cam === null) throw new Error("camera unavailable");
+		const sx = cam.canvasOrigin.x + cam.viewport.widthPx / 2 +
+			(wx - cam.camera.centerX) * cam.camera.scale;
+		const sy = cam.canvasOrigin.y + cam.viewport.heightPx / 2 +
+			(wy - cam.camera.centerY) * cam.camera.scale;
+		return { x: sx, y: sy };
+	}, { wx: x, wy: y });
+}
+
+test("send 2 of 3 ships emits implicit Break + Send into the order draft", async ({
+	page,
+}, testInfo) => {
+	test.skip(
+		testInfo.project.name.startsWith("chromium-mobile"),
+		"phase 20 spec covers desktop layout; mobile inherits the same store",
+	);
+
+	await bootSession(page);
+	await loadSyntheticGame(page);
+
+	// On-planet ship groups are *not* rendered as map primitives (the
+	// renderer hides them to avoid crowding); the player navigates to
+	// them through the planet inspector's stationed-ship row, which
+	// pivots the SelectionStore to the ship-group variant.
+	const earthScreen = await projectWorldToScreen(page, 100, 100);
+	await page.mouse.click(earthScreen.x, earthScreen.y);
+
+	const sidebar = page.getByTestId("sidebar-tool-inspector");
+	await expect(sidebar.getByTestId("inspector-planet-name")).toHaveText("Earth");
+	await sidebar
+		.getByTestId("inspector-planet-ship-groups-select")
+		.first()
+		.click();
+	await expect(
+		sidebar.getByTestId("inspector-ship-group-class"),
+	).toHaveText("Frontier");
+
+	// Open Send.
+	await sidebar.getByTestId("inspector-ship-group-action-send").click();
+	const sendShips = sidebar.getByTestId("inspector-ship-group-form-send-ships");
+	await sendShips.fill("2");
+
+	// Pick Mars on the map.
+	await sidebar.getByTestId("inspector-ship-group-form-send-pick").click();
+	const marsScreen = await projectWorldToScreen(page, 110, 100);
+	await page.mouse.click(marsScreen.x, marsScreen.y);
+	await expect(
+		sidebar.getByTestId("inspector-ship-group-form-send-destination"),
+	).toContainText("Mars");
+
+	// Confirm.
+	await sidebar.getByTestId("inspector-ship-group-form-send-confirm").click();
+
+	// Verify the order tab carries both commands in submission order.
+	await page.getByTestId("sidebar-tab-order").click();
+	const orderTool = page.getByTestId("sidebar-tool-order");
+	await expect(orderTool.getByTestId("order-command-label-0")).toContainText(
+		"split group",
+	);
+	await expect(orderTool.getByTestId("order-command-label-1")).toContainText(
+		"send group",
+	);
+});
diff --git a/ui/frontend/tests/galaxy-client.test.ts b/ui/frontend/tests/galaxy-client.test.ts
index edf9e49..718e6be 100644
--- a/ui/frontend/tests/galaxy-client.test.ts
+++ b/ui/frontend/tests/galaxy-client.test.ts
@@ -217,5 +217,6 @@ function mockCore(opts: MockCoreOptions): Core & {
 		speed: () => 0,
 		cargoCapacity: () => 0,
 		carryingMass: () => 0,
+		blockUpgradeCost: () => 0,
 	};
 }
diff --git a/ui/frontend/tests/helpers/empty-ship-groups.ts b/ui/frontend/tests/helpers/empty-ship-groups.ts
index aeaf15d..acea40d 100644
--- a/ui/frontend/tests/helpers/empty-ship-groups.ts
+++ b/ui/frontend/tests/helpers/empty-ship-groups.ts
@@ -18,10 +18,12 @@ export const EMPTY_SHIP_GROUPS: {
 	incomingShipGroups: ReportIncomingShipGroup[];
 	unidentifiedShipGroups: ReportUnidentifiedShipGroup[];
 	localFleets: ReportLocalFleet[];
+	otherRaces: string[];
 } = {
 	localShipGroups: [],
 	otherShipGroups: [],
 	incomingShipGroups: [],
 	unidentifiedShipGroups: [],
 	localFleets: [],
+	otherRaces: [],
 };
diff --git a/ui/frontend/tests/inspector-ship-group-actions.test.ts b/ui/frontend/tests/inspector-ship-group-actions.test.ts
new file mode 100644
index 0000000..95bc07c
--- /dev/null
+++ b/ui/frontend/tests/inspector-ship-group-actions.test.ts
@@ -0,0 +1,264 @@
+// Vitest coverage for Phase 20's ship-group action panel. Exercises
+// the disabled-with-tooltip rules per action, the implicit-split
+// pattern (an action targeting fewer ships than the group holds
+// emits a `breakShipGroup` command before the action), and the
+// happy-path commits of every variant. The dismantle confirmation
+// for foreign-COL groups lives in its own file
+// (`inspector-ship-group-dismantle-confirm.test.ts`); the modernize
+// cost preview lives in `inspector-ship-group-modernize-cost.test.ts`.
+
+import "@testing-library/jest-dom/vitest";
+import "fake-indexeddb/auto";
+import { fireEvent, render, waitFor } from "@testing-library/svelte";
+import { afterEach, beforeEach, describe, expect, test } from "vitest";
+
+import { i18n } from "../src/lib/i18n/index.svelte";
+import type {
+	ReportLocalFleet,
+	ReportLocalShipGroup,
+	ReportPlanet,
+	ShipClassSummary,
+} from "../src/api/game-state";
+import ShipGroup, {
+	type ShipGroupSelection,
+} from "../src/lib/inspectors/ship-group.svelte";
+import {
+	ORDER_DRAFT_CONTEXT_KEY,
+	OrderDraftStore,
+} from "../src/sync/order-draft.svelte";
+import { IDBCache } from "../src/platform/store/idb-cache";
+import { openGalaxyDB, type GalaxyDB } from "../src/platform/store/idb";
+import type { Cache } from "../src/platform/store/index";
+import type { IDBPDatabase } from "idb";
+
+const GAME_ID = "11111111-2222-3333-4444-555555555555";
+
+let db: IDBPDatabase<GalaxyDB>;
+let dbName: string;
+let cache: Cache;
+let draft: OrderDraftStore;
+
+const PLANETS: ReportPlanet[] = [
+	planet({ number: 17, name: "Castle", x: 100, y: 100, kind: "local" }),
+	planet({ number: 99, name: "Outpost", x: 110, y: 110, kind: "other", owner: "Foreign" }),
+	planet({ number: 33, name: "Reach", x: 150, y: 150, kind: "uninhabited" }),
+];
+
+const SHIP_CLASS_FRONTIER: ShipClassSummary = {
+	name: "Frontier",
+	drive: 5,
+	armament: 0,
+	weapons: 0,
+	shields: 0,
+	cargo: 1,
+};
+
+beforeEach(async () => {
+	dbName = `galaxy-ship-group-actions-${crypto.randomUUID()}`;
+	db = await openGalaxyDB(dbName);
+	cache = new IDBCache(db);
+	draft = new OrderDraftStore();
+	await draft.init({ cache, gameId: GAME_ID });
+	i18n.resetForTests("en");
+});
+
+afterEach(async () => {
+	draft.dispose();
+	db.close();
+	await new Promise<void>((resolve) => {
+		const req = indexedDB.deleteDatabase(dbName);
+		req.onsuccess = () => resolve();
+		req.onerror = () => resolve();
+		req.onblocked = () => resolve();
+	});
+});
+
+function planet(
+	overrides: Partial<ReportPlanet> & Pick<ReportPlanet, "number" | "name" | "x" | "y" | "kind">,
+): ReportPlanet {
+	return {
+		owner: null,
+		size: 1000,
+		resources: 5,
+		industryStockpile: 100,
+		materialsStockpile: 100,
+		industry: 100,
+		population: 100,
+		colonists: 100,
+		production: null,
+		freeIndustry: 100,
+		...overrides,
+	};
+}
+
+function localGroup(
+	overrides: Partial<ReportLocalShipGroup> = {},
+): ReportLocalShipGroup {
+	return {
+		id: "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa",
+		count: 3,
+		class: "Frontier",
+		tech: { drive: 1, weapons: 0, shields: 0, cargo: 1 },
+		cargo: "NONE",
+		load: 0,
+		destination: 17,
+		origin: null,
+		range: null,
+		speed: 0,
+		mass: 12,
+		state: "In_Orbit",
+		fleet: null,
+		...overrides,
+	};
+}
+
+function mount(
+	group: ReportLocalShipGroup,
+	options: {
+		otherRaces?: string[];
+		localFleets?: ReportLocalFleet[];
+		localPlayerDrive?: number;
+	} = {},
+) {
+	const selection: ShipGroupSelection = { variant: "local", group };
+	const context = new Map<unknown, unknown>([
+		[ORDER_DRAFT_CONTEXT_KEY, draft],
+	]);
+	return render(ShipGroup, {
+		props: {
+			selection,
+			planets: PLANETS,
+			localShipClass: [SHIP_CLASS_FRONTIER],
+			localFleets: options.localFleets ?? [],
+			otherRaces: options.otherRaces ?? ["Aliens"],
+			mapWidth: 1000,
+			mapHeight: 1000,
+			localPlayerDrive: options.localPlayerDrive ?? 5,
+			localPlayerWeapons: 1,
+			localPlayerShields: 1,
+			localPlayerCargo: 2,
+		},
+		context,
+	});
+}
+
+describe("ship-group inspector — action enablement", () => {
+	test("non-orbit groups disable every action with the busy tooltip", () => {
+		const ui = mount(localGroup({ state: "In_Space" }));
+		for (const id of [
+			"inspector-ship-group-action-split",
+			"inspector-ship-group-action-send",
+			"inspector-ship-group-action-load",
+			"inspector-ship-group-action-unload",
+			"inspector-ship-group-action-modernize",
+			"inspector-ship-group-action-dismantle",
+			"inspector-ship-group-action-transfer",
+			"inspector-ship-group-action-join-fleet",
+		]) {
+			const button = ui.getByTestId(id);
+			expect(button).toBeDisabled();
+			expect(button.getAttribute("title")).toMatch(/ships are busy/i);
+		}
+	});
+
+	test("send is disabled when no planet is in drive range", () => {
+		const ui = mount(localGroup({ destination: 17 }), { localPlayerDrive: 0 });
+		const button = ui.getByTestId("inspector-ship-group-action-send");
+		expect(button).toBeDisabled();
+		expect(button.getAttribute("title")).toMatch(/no planets are within drive range/i);
+	});
+
+	test("transfer is disabled when there are no other races", () => {
+		const ui = mount(localGroup(), { otherRaces: [] });
+		const button = ui.getByTestId("inspector-ship-group-action-transfer");
+		expect(button).toBeDisabled();
+		expect(button.getAttribute("title")).toMatch(/no other non-extinct races/i);
+	});
+
+	test("unload is disabled when the group carries no cargo", () => {
+		const ui = mount(localGroup({ cargo: "NONE", load: 0 }));
+		const button = ui.getByTestId("inspector-ship-group-action-unload");
+		expect(button).toBeDisabled();
+		expect(button.getAttribute("title")).toMatch(/empty/i);
+	});
+
+	test("unload of colonists is blocked over a foreign planet", () => {
+		const ui = mount(localGroup({ destination: 99, cargo: "COL", load: 1.5 }));
+		const button = ui.getByTestId("inspector-ship-group-action-unload");
+		expect(button).toBeDisabled();
+		expect(button.getAttribute("title")).toMatch(/colonists cannot be unloaded over a foreign planet/i);
+	});
+
+	test("load is blocked over a foreign planet", () => {
+		const ui = mount(localGroup({ destination: 99 }));
+		const button = ui.getByTestId("inspector-ship-group-action-load");
+		expect(button).toBeDisabled();
+		expect(button.getAttribute("title")).toMatch(/own or unowned planets/i);
+	});
+});
+
+describe("ship-group inspector — implicit split + action", () => {
+	test("split with K=1 of 3 emits a single breakShipGroup", async () => {
+		const ui = mount(localGroup({ count: 3 }));
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-split"));
+		const input = ui.getByTestId("inspector-ship-group-form-split-ships") as HTMLInputElement;
+		await fireEvent.input(input, { target: { value: "1" } });
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-form-split-confirm"));
+		await waitFor(() => expect(draft.commands).toHaveLength(1));
+		const cmd = draft.commands[0]!;
+		expect(cmd.kind).toBe("breakShipGroup");
+		if (cmd.kind !== "breakShipGroup") return;
+		expect(cmd.groupId).toBe("aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa");
+		expect(cmd.quantity).toBe(1);
+	});
+
+	test("dismantle on the whole group emits a single dismantleShipGroup", async () => {
+		const ui = mount(localGroup({ count: 2 }));
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-dismantle"));
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-form-dismantle-confirm"));
+		await waitFor(() => expect(draft.commands).toHaveLength(1));
+		const cmd = draft.commands[0]!;
+		expect(cmd.kind).toBe("dismantleShipGroup");
+		if (cmd.kind !== "dismantleShipGroup") return;
+		expect(cmd.groupId).toBe("aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa");
+	});
+
+	test("dismantle on a subset emits implicit Break + Dismantle on the new group", async () => {
+		const ui = mount(localGroup({ count: 3 }));
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-dismantle"));
+		const input = ui.getByTestId("inspector-ship-group-form-dismantle-ships") as HTMLInputElement;
+		await fireEvent.input(input, { target: { value: "2" } });
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-form-dismantle-confirm"));
+		await waitFor(() => expect(draft.commands).toHaveLength(2));
+		const [breakCmd, action] = draft.commands;
+		if (breakCmd?.kind !== "breakShipGroup") throw new Error("expected break first");
+		if (action?.kind !== "dismantleShipGroup") throw new Error("expected dismantle second");
+		expect(breakCmd.groupId).toBe("aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa");
+		expect(breakCmd.quantity).toBe(2);
+		expect(action.groupId).toBe(breakCmd.newGroupId);
+	});
+
+	test("transfer to the only available race emits a transferShipGroup", async () => {
+		const ui = mount(localGroup(), { otherRaces: ["Aliens"] });
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-transfer"));
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-form-transfer-confirm"));
+		await waitFor(() => expect(draft.commands).toHaveLength(1));
+		const cmd = draft.commands[0]!;
+		if (cmd.kind !== "transferShipGroup") throw new Error("wrong kind");
+		expect(cmd.acceptor).toBe("Aliens");
+		expect(cmd.groupId).toBe("aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa");
+	});
+
+	test("join fleet with a fresh name emits joinFleetShipGroup", async () => {
+		const ui = mount(localGroup());
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-join-fleet"));
+		const input = ui.getByTestId("inspector-ship-group-form-join-fleet-new") as HTMLInputElement;
+		await fireEvent.input(input, { target: { value: "Vanguard" } });
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-form-join-fleet-confirm"));
+		await waitFor(() => expect(draft.commands).toHaveLength(1));
+		const cmd = draft.commands[0]!;
+		if (cmd.kind !== "joinFleetShipGroup") throw new Error("wrong kind");
+		expect(cmd.name).toBe("Vanguard");
+		expect(cmd.groupId).toBe("aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa");
+	});
+});
diff --git a/ui/frontend/tests/inspector-ship-group-dismantle-confirm.test.ts b/ui/frontend/tests/inspector-ship-group-dismantle-confirm.test.ts
new file mode 100644
index 0000000..71c1618
--- /dev/null
+++ b/ui/frontend/tests/inspector-ship-group-dismantle-confirm.test.ts
@@ -0,0 +1,201 @@
+// Vitest coverage for the Phase 20 dismantle confirmation. The
+// inspector requires an explicit second click ("colonists die") when
+// the player tries to dismantle a colonist-laden group over a
+// foreign planet — engine rule reference:
+// `controller/ship_group.go.shipGroupDismantle:177-179` (over a
+// foreign planet, `UnloadColonists` is not called and the cargo is
+// lost).
+
+import "@testing-library/jest-dom/vitest";
+import "fake-indexeddb/auto";
+import { fireEvent, render, waitFor } from "@testing-library/svelte";
+import { afterEach, beforeEach, describe, expect, test } from "vitest";
+
+import { i18n } from "../src/lib/i18n/index.svelte";
+import type {
+	ReportLocalShipGroup,
+	ReportPlanet,
+	ShipClassSummary,
+} from "../src/api/game-state";
+import ShipGroup, {
+	type ShipGroupSelection,
+} from "../src/lib/inspectors/ship-group.svelte";
+import {
+	ORDER_DRAFT_CONTEXT_KEY,
+	OrderDraftStore,
+} from "../src/sync/order-draft.svelte";
+import { IDBCache } from "../src/platform/store/idb-cache";
+import { openGalaxyDB, type GalaxyDB } from "../src/platform/store/idb";
+import type { Cache } from "../src/platform/store/index";
+import type { IDBPDatabase } from "idb";
+
+const GAME_ID = "11111111-2222-3333-4444-555555555555";
+
+let db: IDBPDatabase<GalaxyDB>;
+let dbName: string;
+let cache: Cache;
+let draft: OrderDraftStore;
+
+const PLANETS: ReportPlanet[] = [
+	{
+		number: 99,
+		name: "Outpost",
+		x: 100,
+		y: 100,
+		kind: "other",
+		owner: "Foreign",
+		size: 500,
+		resources: 5,
+		industryStockpile: 0,
+		materialsStockpile: 0,
+		industry: 500,
+		population: 500,
+		colonists: 100,
+		production: "Capital",
+		freeIndustry: 500,
+	},
+	{
+		number: 17,
+		name: "Castle",
+		x: 50,
+		y: 50,
+		kind: "local",
+		owner: null,
+		size: 1000,
+		resources: 5,
+		industryStockpile: 0,
+		materialsStockpile: 0,
+		industry: 1000,
+		population: 1000,
+		colonists: 100,
+		production: "Capital",
+		freeIndustry: 1000,
+	},
+];
+
+const SHIP_CLASS_FRONTIER: ShipClassSummary = {
+	name: "Frontier",
+	drive: 5,
+	armament: 0,
+	weapons: 0,
+	shields: 0,
+	cargo: 1,
+};
+
+beforeEach(async () => {
+	dbName = `galaxy-ship-group-dismantle-${crypto.randomUUID()}`;
+	db = await openGalaxyDB(dbName);
+	cache = new IDBCache(db);
+	draft = new OrderDraftStore();
+	await draft.init({ cache, gameId: GAME_ID });
+	i18n.resetForTests("en");
+});
+
+afterEach(async () => {
+	draft.dispose();
+	db.close();
+	await new Promise<void>((resolve) => {
+		const req = indexedDB.deleteDatabase(dbName);
+		req.onsuccess = () => resolve();
+		req.onerror = () => resolve();
+		req.onblocked = () => resolve();
+	});
+});
+
+function group(
+	overrides: Partial<ReportLocalShipGroup> = {},
+): ReportLocalShipGroup {
+	return {
+		id: "bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb",
+		count: 2,
+		class: "Frontier",
+		tech: { drive: 1, weapons: 0, shields: 0, cargo: 1 },
+		cargo: "COL",
+		load: 1.5,
+		destination: 99,
+		origin: null,
+		range: null,
+		speed: 0,
+		mass: 12,
+		state: "In_Orbit",
+		fleet: null,
+		...overrides,
+	};
+}
+
+function mount(g: ReportLocalShipGroup) {
+	const selection: ShipGroupSelection = { variant: "local", group: g };
+	const context = new Map<unknown, unknown>([
+		[ORDER_DRAFT_CONTEXT_KEY, draft],
+	]);
+	return render(ShipGroup, {
+		props: {
+			selection,
+			planets: PLANETS,
+			localShipClass: [SHIP_CLASS_FRONTIER],
+			localFleets: [],
+			otherRaces: ["Aliens"],
+			mapWidth: 1000,
+			mapHeight: 1000,
+			localPlayerDrive: 5,
+			localPlayerWeapons: 1,
+			localPlayerShields: 1,
+			localPlayerCargo: 2,
+		},
+		context,
+	});
+}
+
+describe("ship-group inspector — dismantle confirmation", () => {
+	test("first click on dismantle of foreign-COL group shows the warning and adds nothing", async () => {
+		const ui = mount(group());
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-dismantle"));
+		expect(
+			ui.getByTestId("inspector-ship-group-form-dismantle-warning"),
+		).toBeInTheDocument();
+		const confirm = ui.getByTestId(
+			"inspector-ship-group-form-dismantle-confirm",
+		);
+		expect(confirm).toHaveTextContent(/colonists die/i);
+		await fireEvent.click(confirm);
+		expect(draft.commands).toHaveLength(0);
+	});
+
+	test("second click on the colonists-die confirm emits dismantleShipGroup", async () => {
+		const ui = mount(group());
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-dismantle"));
+		const confirm = ui.getByTestId(
+			"inspector-ship-group-form-dismantle-confirm",
+		);
+		await fireEvent.click(confirm);
+		await fireEvent.click(confirm);
+		await waitFor(() => expect(draft.commands).toHaveLength(1));
+		const cmd = draft.commands[0]!;
+		expect(cmd.kind).toBe("dismantleShipGroup");
+	});
+
+	test("dismantle over own planet skips the warning even with COL aboard", async () => {
+		const ui = mount(group({ destination: 17 }));
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-dismantle"));
+		expect(
+			ui.queryByTestId("inspector-ship-group-form-dismantle-warning"),
+		).toBeNull();
+		await fireEvent.click(
+			ui.getByTestId("inspector-ship-group-form-dismantle-confirm"),
+		);
+		await waitFor(() => expect(draft.commands).toHaveLength(1));
+		expect(draft.commands[0]!.kind).toBe("dismantleShipGroup");
+	});
+
+	test("dismantle over foreign planet without colonists skips the warning", async () => {
+		const ui = mount(group({ cargo: "NONE", load: 0 }));
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-dismantle"));
+		expect(
+			ui.queryByTestId("inspector-ship-group-form-dismantle-warning"),
+		).toBeNull();
+		await fireEvent.click(
+			ui.getByTestId("inspector-ship-group-form-dismantle-confirm"),
+		);
+		await waitFor(() => expect(draft.commands).toHaveLength(1));
+	});
+});
diff --git a/ui/frontend/tests/inspector-ship-group-modernize-cost.test.ts b/ui/frontend/tests/inspector-ship-group-modernize-cost.test.ts
new file mode 100644
index 0000000..b4c5807
--- /dev/null
+++ b/ui/frontend/tests/inspector-ship-group-modernize-cost.test.ts
@@ -0,0 +1,204 @@
+// Vitest coverage for the Phase 20 modernize cost preview. The
+// preview line in the inspector calls `core.blockUpgradeCost` once
+// per ship block and multiplies the per-ship total by the number of
+// targeted ships. The preview hides when `Core` is unavailable; when
+// `tech === "ALL"` the targets are the player's race tech levels;
+// otherwise only the picked block contributes to the cost.
+
+import "@testing-library/jest-dom/vitest";
+import "fake-indexeddb/auto";
+import { fireEvent, render } from "@testing-library/svelte";
+import { afterEach, beforeEach, describe, expect, test } from "vitest";
+
+import { i18n } from "../src/lib/i18n/index.svelte";
+import type {
+	ReportLocalShipGroup,
+	ReportPlanet,
+	ShipClassSummary,
+} from "../src/api/game-state";
+import ShipGroup, {
+	type ShipGroupSelection,
+} from "../src/lib/inspectors/ship-group.svelte";
+import {
+	ORDER_DRAFT_CONTEXT_KEY,
+	OrderDraftStore,
+} from "../src/sync/order-draft.svelte";
+import { CORE_CONTEXT_KEY, CoreHolder } from "../src/lib/core-context.svelte";
+import type { Core } from "../src/platform/core/index";
+import { IDBCache } from "../src/platform/store/idb-cache";
+import { openGalaxyDB, type GalaxyDB } from "../src/platform/store/idb";
+import type { Cache } from "../src/platform/store/index";
+import type { IDBPDatabase } from "idb";
+
+const GAME_ID = "11111111-2222-3333-4444-555555555555";
+
+let db: IDBPDatabase<GalaxyDB>;
+let dbName: string;
+let cache: Cache;
+let draft: OrderDraftStore;
+
+const PLANETS: ReportPlanet[] = [
+	{
+		number: 17,
+		name: "Castle",
+		x: 100,
+		y: 100,
+		kind: "local",
+		owner: null,
+		size: 1000,
+		resources: 5,
+		industryStockpile: 0,
+		materialsStockpile: 0,
+		industry: 1000,
+		population: 1000,
+		colonists: 0,
+		production: "Capital",
+		freeIndustry: 1000,
+	},
+];
+
+const SHIP_CLASS_CRUISER: ShipClassSummary = {
+	name: "Cruiser",
+	drive: 5,
+	armament: 0,
+	weapons: 0,
+	shields: 5,
+	cargo: 5,
+};
+
+beforeEach(async () => {
+	dbName = `galaxy-ship-group-modernize-${crypto.randomUUID()}`;
+	db = await openGalaxyDB(dbName);
+	cache = new IDBCache(db);
+	draft = new OrderDraftStore();
+	await draft.init({ cache, gameId: GAME_ID });
+	i18n.resetForTests("en");
+});
+
+afterEach(async () => {
+	draft.dispose();
+	db.close();
+	await new Promise<void>((resolve) => {
+		const req = indexedDB.deleteDatabase(dbName);
+		req.onsuccess = () => resolve();
+		req.onerror = () => resolve();
+		req.onblocked = () => resolve();
+	});
+});
+
+function group(
+	overrides: Partial<ReportLocalShipGroup> = {},
+): ReportLocalShipGroup {
+	return {
+		id: "cccccccc-cccc-cccc-cccc-cccccccccccc",
+		count: 4,
+		class: "Cruiser",
+		tech: { drive: 1, weapons: 0, shields: 1, cargo: 1 },
+		cargo: "NONE",
+		load: 0,
+		destination: 17,
+		origin: null,
+		range: null,
+		speed: 0,
+		mass: 25,
+		state: "In_Orbit",
+		fleet: null,
+		...overrides,
+	};
+}
+
+// stubCore mirrors `pkg/calc/ship.go.BlockUpgradeCost` exactly so the
+// preview line shows the same number the WASM bridge would produce.
+// The other Core methods are no-ops because the modernize preview
+// only consults `weaponsBlockMass` (returns null when armament is
+// zero) and `blockUpgradeCost`.
+function stubCore(): Core {
+	return {
+		signRequest: () => new Uint8Array(),
+		verifyResponse: () => true,
+		verifyEvent: () => true,
+		verifyPayloadHash: () => true,
+		driveEffective: ({ drive, driveTech }) => drive * driveTech,
+		emptyMass: () => 0,
+		weaponsBlockMass: ({ weapons, armament }) => {
+			if ((armament === 0 && weapons !== 0) || (armament !== 0 && weapons === 0)) {
+				return null;
+			}
+			return (armament + 1) * (weapons / 2);
+		},
+		fullMass: ({ emptyMass, carryingMass }) => emptyMass + carryingMass,
+		speed: () => 0,
+		cargoCapacity: () => 0,
+		carryingMass: () => 0,
+		blockUpgradeCost: ({ blockMass, currentTech, targetTech }) => {
+			if (blockMass === 0 || targetTech <= currentTech) return 0;
+			return (1 - currentTech / targetTech) * 10 * blockMass;
+		},
+	};
+}
+
+function mount(
+	g: ReportLocalShipGroup,
+	options: { core?: Core | null } = {},
+) {
+	const selection: ShipGroupSelection = { variant: "local", group: g };
+	const holder = new CoreHolder();
+	if (options.core !== undefined) holder.set(options.core);
+	const context = new Map<unknown, unknown>([
+		[ORDER_DRAFT_CONTEXT_KEY, draft],
+		[CORE_CONTEXT_KEY, holder],
+	]);
+	return render(ShipGroup, {
+		props: {
+			selection,
+			planets: PLANETS,
+			localShipClass: [SHIP_CLASS_CRUISER],
+			localFleets: [],
+			otherRaces: [],
+			mapWidth: 1000,
+			mapHeight: 1000,
+			localPlayerDrive: 2,
+			localPlayerWeapons: 2,
+			localPlayerShields: 2,
+			localPlayerCargo: 2,
+		},
+		context,
+	});
+}
+
+describe("ship-group inspector — modernize cost preview", () => {
+	test("ALL upgrade preview matches the BlockUpgradeCost formula × ship count", async () => {
+		// drive: mass=5 current=1 target=2 → (1 - 0.5) * 10 * 5 = 25
+		// shields: mass=5 current=1 target=2 → 25
+		// cargo: mass=5 current=1 target=2 → 25
+		// weapons: armament=0 weapons=0 → block mass 0 → 0
+		// per-ship = 75; group of 4 → 300
+		const ui = mount(group(), { core: stubCore() });
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-modernize"));
+		const preview = ui.getByTestId("inspector-ship-group-form-modernize-cost");
+		expect(preview).toHaveTextContent("300");
+	});
+
+	test("per-block tech with custom level uses only that block", async () => {
+		// DRIVE only, target=2: 25 per ship × 4 = 100.
+		const ui = mount(group(), { core: stubCore() });
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-modernize"));
+		await fireEvent.change(
+			ui.getByTestId("inspector-ship-group-form-modernize-tech"),
+			{ target: { value: "DRIVE" } },
+		);
+		await fireEvent.input(
+			ui.getByTestId("inspector-ship-group-form-modernize-level"),
+			{ target: { value: "2" } },
+		);
+		const preview = ui.getByTestId("inspector-ship-group-form-modernize-cost");
+		expect(preview).toHaveTextContent("100");
+	});
+
+	test("preview is unavailable when Core is not loaded", async () => {
+		const ui = mount(group(), { core: null });
+		await fireEvent.click(ui.getByTestId("inspector-ship-group-action-modernize"));
+		const preview = ui.getByTestId("inspector-ship-group-form-modernize-cost");
+		expect(preview).toHaveTextContent(/preview unavailable/i);
+	});
+});
diff --git a/ui/frontend/tests/sync-order-types-ship-group.test.ts b/ui/frontend/tests/sync-order-types-ship-group.test.ts
new file mode 100644
index 0000000..e432081
--- /dev/null
+++ b/ui/frontend/tests/sync-order-types-ship-group.test.ts
@@ -0,0 +1,244 @@
+// Vitest coverage for the Phase 20 ship-group command shapes —
+// `validateCommand` for each of the eight new variants. The
+// validator is invoked through the public `OrderDraftStore.add`
+// path so a regression in either layer surfaces here.
+
+import "fake-indexeddb/auto";
+import { afterEach, beforeEach, describe, expect, test } from "vitest";
+
+import { OrderDraftStore } from "../src/sync/order-draft.svelte";
+import type { OrderCommand } from "../src/sync/order-types";
+import { IDBCache } from "../src/platform/store/idb-cache";
+import { openGalaxyDB, type GalaxyDB } from "../src/platform/store/idb";
+import type { Cache } from "../src/platform/store/index";
+import type { IDBPDatabase } from "idb";
+
+const GAME_ID = "11111111-2222-3333-4444-555555555555";
+const GROUP_ID = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa";
+const NEW_GROUP_ID = "bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb";
+
+let db: IDBPDatabase<GalaxyDB>;
+let dbName: string;
+let cache: Cache;
+let draft: OrderDraftStore;
+
+beforeEach(async () => {
+	dbName = `galaxy-validate-ship-group-${crypto.randomUUID()}`;
+	db = await openGalaxyDB(dbName);
+	cache = new IDBCache(db);
+	draft = new OrderDraftStore();
+	await draft.init({ cache, gameId: GAME_ID });
+});
+
+afterEach(async () => {
+	draft.dispose();
+	db.close();
+	await new Promise<void>((resolve) => {
+		const req = indexedDB.deleteDatabase(dbName);
+		req.onsuccess = () => resolve();
+		req.onerror = () => resolve();
+		req.onblocked = () => resolve();
+	});
+});
+
+async function statusOf(cmd: OrderCommand): Promise<string> {
+	await draft.add(cmd);
+	return draft.statuses[cmd.id]!;
+}
+
+describe("validateCommand — ship-group variants", () => {
+	test("breakShipGroup with positive quantity is valid", async () => {
+		expect(
+			await statusOf({
+				kind: "breakShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				newGroupId: NEW_GROUP_ID,
+				quantity: 2,
+			}),
+		).toBe("valid");
+	});
+
+	test("breakShipGroup with quantity 0 is invalid", async () => {
+		expect(
+			await statusOf({
+				kind: "breakShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				newGroupId: NEW_GROUP_ID,
+				quantity: 0,
+			}),
+		).toBe("invalid");
+	});
+
+	test("breakShipGroup with same source and new id is invalid", async () => {
+		expect(
+			await statusOf({
+				kind: "breakShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				newGroupId: GROUP_ID,
+				quantity: 1,
+			}),
+		).toBe("invalid");
+	});
+
+	test("sendShipGroup with positive destination is valid", async () => {
+		expect(
+			await statusOf({
+				kind: "sendShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				destinationPlanetNumber: 7,
+			}),
+		).toBe("valid");
+	});
+
+	test("sendShipGroup to planet 0 is invalid", async () => {
+		expect(
+			await statusOf({
+				kind: "sendShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				destinationPlanetNumber: 0,
+			}),
+		).toBe("invalid");
+	});
+
+	test("loadShipGroup with valid cargo and quantity is valid", async () => {
+		expect(
+			await statusOf({
+				kind: "loadShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				cargo: "COL",
+				quantity: 1.5,
+			}),
+		).toBe("valid");
+	});
+
+	test("loadShipGroup with zero quantity is invalid", async () => {
+		expect(
+			await statusOf({
+				kind: "loadShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				cargo: "COL",
+				quantity: 0,
+			}),
+		).toBe("invalid");
+	});
+
+	test("unloadShipGroup with positive quantity is valid", async () => {
+		expect(
+			await statusOf({
+				kind: "unloadShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				quantity: 0.5,
+			}),
+		).toBe("valid");
+	});
+
+	test("upgradeShipGroup ALL with level 0 is valid", async () => {
+		expect(
+			await statusOf({
+				kind: "upgradeShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				tech: "ALL",
+				level: 0,
+			}),
+		).toBe("valid");
+	});
+
+	test("upgradeShipGroup ALL with non-zero level is invalid", async () => {
+		expect(
+			await statusOf({
+				kind: "upgradeShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				tech: "ALL",
+				level: 2,
+			}),
+		).toBe("invalid");
+	});
+
+	test("upgradeShipGroup DRIVE with positive level is valid", async () => {
+		expect(
+			await statusOf({
+				kind: "upgradeShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				tech: "DRIVE",
+				level: 1.5,
+			}),
+		).toBe("valid");
+	});
+
+	test("upgradeShipGroup DRIVE with level 0 is invalid", async () => {
+		expect(
+			await statusOf({
+				kind: "upgradeShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				tech: "DRIVE",
+				level: 0,
+			}),
+		).toBe("invalid");
+	});
+
+	test("dismantleShipGroup with valid uuid is valid", async () => {
+		expect(
+			await statusOf({
+				kind: "dismantleShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+			}),
+		).toBe("valid");
+	});
+
+	test("transferShipGroup with valid acceptor name is valid", async () => {
+		expect(
+			await statusOf({
+				kind: "transferShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				acceptor: "Aliens",
+			}),
+		).toBe("valid");
+	});
+
+	test("transferShipGroup with empty acceptor is invalid", async () => {
+		expect(
+			await statusOf({
+				kind: "transferShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				acceptor: "",
+			}),
+		).toBe("invalid");
+	});
+
+	test("joinFleetShipGroup with valid name is valid", async () => {
+		expect(
+			await statusOf({
+				kind: "joinFleetShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				name: "Vanguard",
+			}),
+		).toBe("valid");
+	});
+
+	test("joinFleetShipGroup with empty name is invalid", async () => {
+		expect(
+			await statusOf({
+				kind: "joinFleetShipGroup",
+				id: crypto.randomUUID(),
+				groupId: GROUP_ID,
+				name: "",
+			}),
+		).toBe("invalid");
+	});
+});
diff --git a/ui/frontend/tests/sync-submit-ship-group.test.ts b/ui/frontend/tests/sync-submit-ship-group.test.ts
new file mode 100644
index 0000000..95b0a33
--- /dev/null
+++ b/ui/frontend/tests/sync-submit-ship-group.test.ts
@@ -0,0 +1,266 @@
+// Vitest round-trip coverage for the eight Phase 20 ship-group
+// command shapes. The encoder lives in `sync/submit.ts`; the
+// decoder lives in `sync/order-load.ts`. We capture the request
+// bytes the encoder produces, re-emit them inside a
+// `UserGamesOrderGetResponse` envelope, and feed that to
+// `fetchOrder`. The decoded command must match the original — any
+// drift between encoder and decoder fails here first.
+
+import { Builder, ByteBuffer } from "flatbuffers";
+import { describe, expect, test, vi } from "vitest";
+
+import type { GalaxyClient } from "../src/api/galaxy-client";
+import { uuidToHiLo } from "../src/api/game-state";
+import { UUID } from "../src/proto/galaxy/fbs/common";
+import {
+	CommandItem,
+	CommandPayload,
+	CommandShipGroupBreak,
+	CommandShipGroupDismantle,
+	CommandShipGroupJoinFleet,
+	CommandShipGroupLoad,
+	CommandShipGroupSend,
+	CommandShipGroupTransfer,
+	CommandShipGroupUnload,
+	CommandShipGroupUpgrade,
+	UserGamesOrder,
+	UserGamesOrderGetResponse,
+	UserGamesOrderResponse,
+} from "../src/proto/galaxy/fbs/order";
+import { fetchOrder } from "../src/sync/order-load";
+import { submitOrder } from "../src/sync/submit";
+import type { OrderCommand } from "../src/sync/order-types";
+
+const GAME_ID = "11111111-2222-3333-4444-555555555555";
+const GROUP_ID = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa";
+
+function mockClient(
+	executeCommand: (
+		messageType: string,
+		payload: Uint8Array,
+	) => Promise<{ resultCode: string; payloadBytes: Uint8Array }>,
+): GalaxyClient {
+	return { executeCommand } as unknown as GalaxyClient;
+}
+
+// captureRequestBytes runs submitOrder against a mock that records
+// the outgoing payload, then returns those bytes (which are a valid
+// `UserGamesOrder` envelope).
+async function captureRequestBytes(cmds: OrderCommand[]): Promise<Uint8Array> {
+	let captured: Uint8Array | null = null;
+	const exec = vi.fn(async (_msg: string, payload: Uint8Array) => {
+		captured = payload;
+		const builder = new Builder(64);
+		const [hi, lo] = uuidToHiLo(GAME_ID);
+		const gameIdOffset = UUID.createUUID(builder, hi, lo);
+		UserGamesOrderResponse.startUserGamesOrderResponse(builder);
+		UserGamesOrderResponse.addGameId(builder, gameIdOffset);
+		UserGamesOrderResponse.addUpdatedAt(builder, BigInt(0));
+		const offset = UserGamesOrderResponse.endUserGamesOrderResponse(builder);
+		builder.finish(offset);
+		return { resultCode: "ok", payloadBytes: builder.asUint8Array() };
+	});
+	const result = await submitOrder(mockClient(exec), GAME_ID, cmds);
+	expect(result.ok).toBe(true);
+	expect(captured).not.toBeNull();
+	return captured!;
+}
+
+// wrapAsGetResponse rebuilds the captured `UserGamesOrder` inside a
+// `UserGamesOrderGetResponse` envelope by walking each
+// `CommandItem`, copying its identity fields, and re-packing each
+// payload through `unpack().pack(builder)` — the FBS-generated
+// helper that round-trips a typed table into a fresh builder.
+function wrapAsGetResponse(orderBytes: Uint8Array): Uint8Array {
+	const order = UserGamesOrder.getRootAsUserGamesOrder(
+		new ByteBuffer(orderBytes),
+	);
+	const builder = new Builder(256);
+	const itemOffsets: number[] = [];
+	for (let i = 0; i < order.commandsLength(); i++) {
+		const item = order.commands(i);
+		if (item === null) continue;
+		const cmdIdOffset = builder.createString(item.cmdId() ?? "");
+		const payloadType = item.payloadType();
+		const payloadOffset = packPayload(builder, item, payloadType);
+		CommandItem.startCommandItem(builder);
+		CommandItem.addCmdId(builder, cmdIdOffset);
+		CommandItem.addPayloadType(builder, payloadType);
+		CommandItem.addPayload(builder, payloadOffset);
+		itemOffsets.push(CommandItem.endCommandItem(builder));
+	}
+	const commandsVec = UserGamesOrder.createCommandsVector(builder, itemOffsets);
+	const [hi, lo] = uuidToHiLo(GAME_ID);
+	const gameIdOffset = UUID.createUUID(builder, hi, lo);
+	UserGamesOrder.startUserGamesOrder(builder);
+	UserGamesOrder.addGameId(builder, gameIdOffset);
+	UserGamesOrder.addUpdatedAt(builder, order.updatedAt());
+	UserGamesOrder.addCommands(builder, commandsVec);
+	const orderOffset = UserGamesOrder.endUserGamesOrder(builder);
+
+	UserGamesOrderGetResponse.startUserGamesOrderGetResponse(builder);
+	UserGamesOrderGetResponse.addFound(builder, true);
+	UserGamesOrderGetResponse.addOrder(builder, orderOffset);
+	const resOffset =
+		UserGamesOrderGetResponse.endUserGamesOrderGetResponse(builder);
+	builder.finish(resOffset);
+	return builder.asUint8Array();
+}
+
+function packPayload(
+	builder: Builder,
+	item: NonNullable<ReturnType<UserGamesOrder["commands"]>>,
+	payloadType: CommandPayload,
+): number {
+	switch (payloadType) {
+		case CommandPayload.CommandShipGroupBreak: {
+			const inner = new CommandShipGroupBreak();
+			item.payload(inner);
+			return inner.unpack().pack(builder);
+		}
+		case CommandPayload.CommandShipGroupSend: {
+			const inner = new CommandShipGroupSend();
+			item.payload(inner);
+			return inner.unpack().pack(builder);
+		}
+		case CommandPayload.CommandShipGroupLoad: {
+			const inner = new CommandShipGroupLoad();
+			item.payload(inner);
+			return inner.unpack().pack(builder);
+		}
+		case CommandPayload.CommandShipGroupUnload: {
+			const inner = new CommandShipGroupUnload();
+			item.payload(inner);
+			return inner.unpack().pack(builder);
+		}
+		case CommandPayload.CommandShipGroupUpgrade: {
+			const inner = new CommandShipGroupUpgrade();
+			item.payload(inner);
+			return inner.unpack().pack(builder);
+		}
+		case CommandPayload.CommandShipGroupDismantle: {
+			const inner = new CommandShipGroupDismantle();
+			item.payload(inner);
+			return inner.unpack().pack(builder);
+		}
+		case CommandPayload.CommandShipGroupTransfer: {
+			const inner = new CommandShipGroupTransfer();
+			item.payload(inner);
+			return inner.unpack().pack(builder);
+		}
+		case CommandPayload.CommandShipGroupJoinFleet: {
+			const inner = new CommandShipGroupJoinFleet();
+			item.payload(inner);
+			return inner.unpack().pack(builder);
+		}
+		default:
+			throw new Error(`unsupported payload type ${payloadType}`);
+	}
+}
+
+async function roundTrip(cmd: OrderCommand): Promise<OrderCommand> {
+	const requestBytes = await captureRequestBytes([cmd]);
+	const responseBytes = wrapAsGetResponse(requestBytes);
+	const exec = vi.fn(async () => ({
+		resultCode: "ok",
+		payloadBytes: responseBytes,
+	}));
+	const result = await fetchOrder(mockClient(exec), GAME_ID, 0);
+	expect(result.commands).toHaveLength(1);
+	return result.commands[0]!;
+}
+
+describe("submit + order-load round-trip — ship-group commands", () => {
+	test("breakShipGroup", async () => {
+		const cmd: OrderCommand = {
+			kind: "breakShipGroup",
+			id: crypto.randomUUID(),
+			groupId: GROUP_ID,
+			newGroupId: "11112222-3333-4444-5555-666677778888",
+			quantity: 3,
+		};
+		expect(await roundTrip(cmd)).toEqual(cmd);
+	});
+
+	test("sendShipGroup", async () => {
+		const cmd: OrderCommand = {
+			kind: "sendShipGroup",
+			id: crypto.randomUUID(),
+			groupId: GROUP_ID,
+			destinationPlanetNumber: 42,
+		};
+		expect(await roundTrip(cmd)).toEqual(cmd);
+	});
+
+	test("loadShipGroup", async () => {
+		const cmd: OrderCommand = {
+			kind: "loadShipGroup",
+			id: crypto.randomUUID(),
+			groupId: GROUP_ID,
+			cargo: "MAT",
+			quantity: 12.5,
+		};
+		expect(await roundTrip(cmd)).toEqual(cmd);
+	});
+
+	test("unloadShipGroup", async () => {
+		const cmd: OrderCommand = {
+			kind: "unloadShipGroup",
+			id: crypto.randomUUID(),
+			groupId: GROUP_ID,
+			quantity: 6.5,
+		};
+		expect(await roundTrip(cmd)).toEqual(cmd);
+	});
+
+	test("upgradeShipGroup ALL", async () => {
+		const cmd: OrderCommand = {
+			kind: "upgradeShipGroup",
+			id: crypto.randomUUID(),
+			groupId: GROUP_ID,
+			tech: "ALL",
+			level: 0,
+		};
+		expect(await roundTrip(cmd)).toEqual(cmd);
+	});
+
+	test("upgradeShipGroup DRIVE level 1.5", async () => {
+		const cmd: OrderCommand = {
+			kind: "upgradeShipGroup",
+			id: crypto.randomUUID(),
+			groupId: GROUP_ID,
+			tech: "DRIVE",
+			level: 1.5,
+		};
+		expect(await roundTrip(cmd)).toEqual(cmd);
+	});
+
+	test("dismantleShipGroup", async () => {
+		const cmd: OrderCommand = {
+			kind: "dismantleShipGroup",
+			id: crypto.randomUUID(),
+			groupId: GROUP_ID,
+		};
+		expect(await roundTrip(cmd)).toEqual(cmd);
+	});
+
+	test("transferShipGroup", async () => {
+		const cmd: OrderCommand = {
+			kind: "transferShipGroup",
+			id: crypto.randomUUID(),
+			groupId: GROUP_ID,
+			acceptor: "Aliens",
+		};
+		expect(await roundTrip(cmd)).toEqual(cmd);
+	});
+
+	test("joinFleetShipGroup", async () => {
+		const cmd: OrderCommand = {
+			kind: "joinFleetShipGroup",
+			id: crypto.randomUUID(),
+			groupId: GROUP_ID,
+			name: "Vanguard",
+		};
+		expect(await roundTrip(cmd)).toEqual(cmd);
+	});
+});
diff --git a/ui/wasm/main.go b/ui/wasm/main.go
index 7bc311c..dfb13b2 100644
--- a/ui/wasm/main.go
+++ b/ui/wasm/main.go
@@ -25,6 +25,7 @@
 //   - speed(fields)             -> number
 //   - cargoCapacity(fields)     -> number
 //   - carryingMass(fields)      -> number
+//   - blockUpgradeCost(fields)  -> number          (Phase 20: modernize cost preview)
 //
 // Field objects are plain JS objects with camelCase keys matching the
 // TypeScript `Core` interface, and bytes fields are Uint8Array.
@@ -59,6 +60,7 @@ func main() {
 		"speed":             js.FuncOf(speed),
 		"cargoCapacity":     js.FuncOf(cargoCapacity),
 		"carryingMass":      js.FuncOf(carryingMass),
+		"blockUpgradeCost":  js.FuncOf(blockUpgradeCost),
 	}))
 
 	// Block forever so the Go runtime stays alive while JS keeps calling
@@ -224,6 +226,21 @@ func carryingMass(_ js.Value, args []js.Value) any {
 	return js.ValueOf(calc.CarryingMass(load, cargoTech))
 }
 
+// blockUpgradeCost bridges `calc.BlockUpgradeCost`. Input
+// `{ blockMass, currentTech, targetTech }`, output a JS number
+// (production cost of moving one block from currentTech to
+// targetTech; zero when blockMass is zero or targetTech is not
+// above currentTech).
+func blockUpgradeCost(_ js.Value, args []js.Value) any {
+	if len(args) != 1 {
+		return js.Null()
+	}
+	blockMass := args[0].Get("blockMass").Float()
+	currentTech := args[0].Get("currentTech").Float()
+	targetTech := args[0].Get("targetTech").Float()
+	return js.ValueOf(calc.BlockUpgradeCost(blockMass, currentTech, targetTech))
+}
+
 // copyBytesFromJS materialises a JS Uint8Array (or any indexable
 // byte-shaped value) into a Go byte slice. We avoid `js.CopyBytesToGo`
 // because TinyGo's implementation panics on values it does not