diff --git a/scenes/planet/planet.gd b/scenes/planet/planet.gd
index 9565e30..7cdb576 100644
--- a/scenes/planet/planet.gd
+++ b/scenes/planet/planet.gd
@@ -20,13 +20,6 @@ var player: Player :
 func _ready() -> void:
 	is_selected = false
 
-func _on_game_start(game: GameLogic) -> void:
-	pass
-
-func _on_game_tick(game: GameLogic, tick: int) -> void:
-	if player != game.neutral_player and tick % 10 == 0:
-		population += 1
-
 @export_category("UI")
 
 signal selected(planet: Planet)
diff --git a/scenes/player/player.gd b/scenes/player/player.gd
index 1cf2611..c866ed7 100644
--- a/scenes/player/player.gd
+++ b/scenes/player/player.gd
@@ -5,6 +5,8 @@ class_name Player
 
 @export var icon: Texture2D
 
+var pending_operations: Array[GameOperation] = []
+
 func _on_game_start(game: GameLogic) -> void:
 	pass
 
diff --git a/scripts/game_logic.gd b/scripts/game_logic.gd
index 5c21c80..e6d109b 100644
--- a/scripts/game_logic.gd
+++ b/scripts/game_logic.gd
@@ -1,8 +1,8 @@
 extends Node
 class_name GameLogic
 
-const LOGIC_TICKS_PER_SECOND: float = 20.;
-const LOGIC_SECONDS_PER_TICK = 1. / LOGIC_TICKS_PER_SECOND;
+const LOGIC_TICKS_PER_SECOND: float = 20.
+const LOGIC_SECONDS_PER_TICK = 1. / LOGIC_TICKS_PER_SECOND
 
 ## Neutral player owning all non-conquered planets.
 @export var neutral_player: Player
@@ -23,6 +23,14 @@ func _ready() -> void:
 	_game_init()
 	game_start.emit(self)
 
+func _process(delta: float) -> void:
+	extra_time += delta
+	
+	while extra_time > LOGIC_SECONDS_PER_TICK:
+		extra_time -= LOGIC_SECONDS_PER_TICK
+		_game_tick(ticks_count)
+		ticks_count += 1
+
 func _game_init() -> void:
 	ticks_count = 0
 	extra_time = 0.
@@ -35,13 +43,27 @@ func _game_init() -> void:
 		var planet := planets[i]
 		planet.player = players[i] if i < players.size() else neutral_player
 		planet.is_selected = false
-		game_start.connect(planet._on_game_start)
-		game_tick.connect(planet._on_game_tick)
 
-func _process(delta: float) -> void:
-	extra_time += delta
-	
-	while extra_time > LOGIC_SECONDS_PER_TICK:
-		extra_time -= LOGIC_SECONDS_PER_TICK
-		game_tick.emit(self, ticks_count)
-		ticks_count += 1
+func _game_tick(tick: int) -> void:
+	for planet in planets:
+		if planet.player != neutral_player and tick % 10 == 0:
+			planet.population += 1
+
+	for player in players:
+		for op in player.pending_operations:
+			if op is GameOperationSendFleet:
+				var count = min(op.max_count, op.from.population)
+				op.from.population -= count
+				if op.from.player == op.to.player:
+					op.to.population += count
+				else:
+					op.to.population -= count
+					if op.to.population <= 0:
+						op.to.player = op.from.player
+						op.to.population = abs(op.from.population)
+			else:
+				assert(false, "Unknown GameOperation: %s" % [op])
+
+		player.pending_operations.clear()
+
+	game_tick.emit(self, tick)
diff --git a/scripts/game_operation.gd b/scripts/game_operation.gd
new file mode 100644
index 0000000..01f358d
--- /dev/null
+++ b/scripts/game_operation.gd
@@ -0,0 +1,2 @@
+extends RefCounted
+class_name GameOperation
diff --git a/scripts/game_operation_send_fleet.gd b/scripts/game_operation_send_fleet.gd
new file mode 100644
index 0000000..acadd45
--- /dev/null
+++ b/scripts/game_operation_send_fleet.gd
@@ -0,0 +1,8 @@
+extends GameOperation
+class_name GameOperationSendFleet
+
+var from: Planet
+
+var to: Planet
+
+var max_count: int
diff --git a/ui.gd b/ui.gd
index c884bb5..a5800c1 100644
--- a/ui.gd
+++ b/ui.gd
@@ -5,10 +5,6 @@ class_name GameUI
 
 var game: GameLogic
 
-var selected_planet: Planet
-var pointed_planet: Planet
-var dragging_from_planet: bool
-var last_cursor_position: Vector2
 
 func _on_game_started(game: GameLogic) -> void:
 	self.game = game
@@ -18,7 +14,41 @@ func _on_game_started(game: GameLogic) -> void:
 		planet.pointer_entered.connect(_on_planet_pointer_entered)
 		planet.pointer_exited.connect(_on_planet_pointer_exited)
 
-	#trail.color = game.player
+func _process(delta: float) -> void:
+	_update_trail(delta, false)
+
+func _unhandled_input(event: InputEvent) -> void:
+	if event is InputEventMouse:
+		_handle_mouse_input(event)
+
+#region Mouse input
+
+var last_cursor_position: Vector2
+
+func _handle_mouse_input(event: InputEventMouse) -> void:
+	if event is InputEventMouseMotion:
+		# The trail follows the cursor.
+		last_cursor_position = event.global_position
+
+	if event is InputEventMouseButton and event.button_index == MOUSE_BUTTON_LEFT and event.is_released():
+		# The trail disappears when no longer dragging.
+		dragging_from_planet = false
+		
+		# Detect mouse released on a planet and spawn a fleet.
+		if selected_planet != null and selected_planet.player is LocalPlayer and pointed_planet != null:
+			var op := GameOperationSendFleet.new()
+			op.from = selected_planet
+			op.to = pointed_planet
+			op.max_count = ceil(selected_planet.population / 2)
+			selected_planet.player.pending_operations.push_front(op)
+
+#endregion
+
+#region Planets
+
+var selected_planet: Planet
+var pointed_planet: Planet
+var dragging_from_planet: bool
 
 func _on_planet_selected(planet: Planet) -> void:
 	if selected_planet != null:
@@ -37,26 +67,7 @@ func _on_planet_pointer_exited(planet: Planet) -> void:
 	if pointed_planet == planet:
 		pointed_planet = null
 
-func _unhandled_input(event: InputEvent) -> void:
-	if event is InputEventMouseMotion:
-		# The trail follows the cursor.
-		last_cursor_position = event.global_position
-
-	if event is InputEventMouseButton and event.button_index == MOUSE_BUTTON_LEFT and event.is_released():
-		# The trail disappears when no longer dragging.
-		dragging_from_planet = false
-		
-		# Detect mouse released on a planet and spawn a fleet.
-		if selected_planet != null and selected_planet.player is LocalPlayer and pointed_planet != null:
-			var count = ceil(selected_planet.population / 2)
-			selected_planet.population -= count
-			if selected_planet.player == pointed_planet.player:
-				pointed_planet.population += count
-			else:
-				pointed_planet.population -= count
-				if pointed_planet.population <= 0:
-					pointed_planet.player = selected_planet.player
-					pointed_planet.population = abs(pointed_planet.population)
+#endregion
 
 #region Trail
 
@@ -75,6 +86,3 @@ func _update_trail(delta: float, snap_position: bool) -> void:
 			trail.end_position = target_position if snap_position else Util.damp(trail.end_position, target_position, 1e-20, delta)
 
 #endregion
-
-func _process(delta: float) -> void:
-	_update_trail(delta, false)