diff --git a/TODO b/TODO
index ca94cbb..5dabd26 100644
--- a/TODO
+++ b/TODO
@@ -1,3 +1,4 @@
+* Enable strict null checking in typescript
 * Ensure that tweens and particle emitters get destroyed once animation is done (or view changes)
 * Highlight ships that will be included as target of current action
 * Controls: Do not focus on ship while targetting for area effects (dissociate hover and target)
@@ -27,7 +28,6 @@
 * TacticalAI: allow to play several moves in the same turn
 * TacticalAI: add pauses to not play too quickly
 * TacticalAI: replace BullyAI
-* AIDuel: fix first AI always winning when two identical AIs are selected
 * Add a defeat screen (game over for now)
 * Add a victory screen, with loot display
 * Add retreat from battle
diff --git a/src/core/MoveFireSimulator.spec.ts b/src/core/MoveFireSimulator.spec.ts
index 3531a2a..3b94779 100644
--- a/src/core/MoveFireSimulator.spec.ts
+++ b/src/core/MoveFireSimulator.spec.ts
@@ -89,5 +89,14 @@ module TS.SpaceTac.Specs {
                 { action: jasmine.objectContaining({ code: "fire-null" }), target: new Target(ship.arena_x + 18, ship.arena_y, null), ap: 2 }
             ]);
         });
+
+        it("does nothing if trying to move in the same spot", function () {
+            let [ship, simulator, action] = simpleWeaponCase();
+            let result = simulator.simulateAction(ship.listEquipment(SlotType.Engine)[0].action, new Target(ship.arena_x, ship.arena_y, null));
+            expect(result.success).toBe(true);
+            expect(result.need_move).toBe(false);
+            expect(result.need_fire).toBe(false);
+            expect(result.parts).toEqual([]);
+        });
     });
 }
diff --git a/src/core/MoveFireSimulator.ts b/src/core/MoveFireSimulator.ts
index 4c1c9bb..ef0593c 100644
--- a/src/core/MoveFireSimulator.ts
+++ b/src/core/MoveFireSimulator.ts
@@ -59,27 +59,32 @@ module TS.SpaceTac {
          * Simulate a given action on a given valid target.
          */
         simulateAction(action: BaseAction, target: Target): MoveFireResult {
+            let result = new MoveFireResult();
+
             let dx = target.x - this.ship.arena_x;
             let dy = target.y - this.ship.arena_y;
             let distance = Math.sqrt(dx * dx + dy * dy);
-            let result = new MoveFireResult();
+
             let ap = this.ship.values.power.get();
             let action_radius = action.getRangeRadius(this.ship);
 
             if (action instanceof MoveAction || distance > action_radius) {
-                result.need_move = true;
                 let move_distance = action instanceof MoveAction ? distance : distance - action_radius;
-                let move_target = new Target(this.ship.arena_x + dx * move_distance / distance, this.ship.arena_y + dy * move_distance / distance, null);
-                let engine = this.findBestEngine();
-                if (engine) {
-                    result.total_move_ap = engine.action.getActionPointsUsage(this.ship.getBattle(), this.ship, move_target);
-                    result.can_move = ap > 0;
-                    result.can_end_move = result.total_move_ap <= ap;
-                    result.move_location = move_target;
-                    result.parts.push({ action: engine.action, target: move_target, ap: result.total_move_ap });
+                if (move_distance > 0.000001) {
+                    result.need_move = true;
 
-                    ap -= result.total_move_ap;
-                    distance -= move_distance;
+                    let move_target = new Target(this.ship.arena_x + dx * move_distance / distance, this.ship.arena_y + dy * move_distance / distance, null);
+                    let engine = this.findBestEngine();
+                    if (engine) {
+                        result.total_move_ap = engine.action.getActionPointsUsage(this.ship, move_target);
+                        result.can_move = ap > 0;
+                        result.can_end_move = result.total_move_ap <= ap;
+                        result.move_location = move_target;
+                        result.parts.push({ action: engine.action, target: move_target, ap: result.total_move_ap });
+
+                        ap -= result.total_move_ap;
+                        distance -= move_distance;
+                    }
                 }
             }
 
@@ -87,7 +92,7 @@ module TS.SpaceTac {
                 result.success = true;
                 if (!(action instanceof MoveAction)) {
                     result.need_fire = true;
-                    result.total_fire_ap = action.getActionPointsUsage(this.ship.getBattle(), this.ship, target);
+                    result.total_fire_ap = action.getActionPointsUsage(this.ship, target);
                     result.can_fire = result.total_fire_ap <= ap;
                     result.fire_location = target;
                     result.parts.push({ action: action, target: target, ap: result.total_fire_ap });
diff --git a/src/core/actions/BaseAction.spec.ts b/src/core/actions/BaseAction.spec.ts
index 579b45b..3abb062 100644
--- a/src/core/actions/BaseAction.spec.ts
+++ b/src/core/actions/BaseAction.spec.ts
@@ -8,22 +8,22 @@ module TS.SpaceTac {
             ship.addSlot(SlotType.Hull).attach(equipment);
             ship.values.power.setMaximal(10);
 
-            expect(action.canBeUsed(null, ship)).toBe(false);
+            expect(action.checkCannotBeApplied(ship)).toBe("not enough power");
 
             ship.values.power.set(5);
 
-            expect(action.canBeUsed(null, ship)).toBe(true);
-            expect(action.canBeUsed(null, ship, 4)).toBe(true);
-            expect(action.canBeUsed(null, ship, 3)).toBe(true);
-            expect(action.canBeUsed(null, ship, 2)).toBe(false);
+            expect(action.checkCannotBeApplied(ship)).toBe(null);
+            expect(action.checkCannotBeApplied(ship, 4)).toBe(null);
+            expect(action.checkCannotBeApplied(ship, 3)).toBe(null);
+            expect(action.checkCannotBeApplied(ship, 2)).toBe("not enough power");
 
             ship.values.power.set(3);
 
-            expect(action.canBeUsed(null, ship)).toBe(true);
+            expect(action.checkCannotBeApplied(ship)).toBe(null);
 
             ship.values.power.set(2);
 
-            expect(action.canBeUsed(null, ship)).toBe(false);
+            expect(action.checkCannotBeApplied(ship)).toBe("not enough power");
         });
     });
 }
diff --git a/src/core/actions/BaseAction.ts b/src/core/actions/BaseAction.ts
index a364e05..f527efd 100644
--- a/src/core/actions/BaseAction.ts
+++ b/src/core/actions/BaseAction.ts
@@ -21,12 +21,18 @@ module TS.SpaceTac {
             this.equipment = equipment;
         }
 
-        // Check basic conditions to know if the ship can use this action at all
-        //  Method to reimplement to set conditions
-        canBeUsed(battle: Battle, ship: Ship, remaining_ap: number = null): boolean {
+        /**
+         * Check basic conditions to know if the ship can use this action at all
+         * 
+         * Method to extend to set conditions
+         * 
+         * Returns an informative message indicating why the action cannot be used, null otherwise
+         */
+        checkCannotBeApplied(ship: Ship, remaining_ap: number = null): string | null {
+            let battle = ship.getBattle();
             if (battle && battle.playing_ship !== ship) {
                 // Ship is not playing
-                return false;
+                return "ship not playing";
             }
 
             // Check AP usage
@@ -34,11 +40,15 @@ module TS.SpaceTac {
                 remaining_ap = ship.values.power.get();
             }
             var ap_usage = this.equipment ? this.equipment.ap_usage : 0;
-            return remaining_ap >= ap_usage;
+            if (remaining_ap >= ap_usage) {
+                return null;
+            } else {
+                return "not enough power";
+            }
         }
 
         // Get the number of action points the action applied to a target would use
-        getActionPointsUsage(battle: Battle, ship: Ship, target: Target): number {
+        getActionPointsUsage(ship: Ship, target: Target): number {
             if (this.equipment) {
                 return this.equipment.ap_usage;
             } else {
@@ -66,14 +76,14 @@ module TS.SpaceTac {
 
         // Method to check if a target is applicable for this action
         //  Will call checkLocationTarget or checkShipTarget by default
-        checkTarget(battle: Battle, ship: Ship, target: Target): Target {
-            if (!this.canBeUsed(battle, ship)) {
+        checkTarget(ship: Ship, target: Target): Target {
+            if (this.checkCannotBeApplied(ship)) {
                 return null;
             } else if (target) {
                 if (target.ship) {
-                    return this.checkShipTarget(battle, ship, target);
+                    return this.checkShipTarget(ship, target);
                 } else {
-                    return this.checkLocationTarget(battle, ship, target);
+                    return this.checkLocationTarget(ship, target);
                 }
             } else {
                 return null;
@@ -82,38 +92,42 @@ module TS.SpaceTac {
 
         // Method to reimplement to check if a space target is applicable
         //  Must return null if the target can't be applied, an altered target, or the original target
-        checkLocationTarget(battle: Battle, ship: Ship, target: Target): Target {
+        checkLocationTarget(ship: Ship, target: Target): Target {
             return null;
         }
 
         // Method to reimplement to check if a ship target is applicable
         //  Must return null if the target can't be applied, an altered target, or the original target
-        checkShipTarget(battle: Battle, ship: Ship, target: Target): Target {
+        checkShipTarget(ship: Ship, target: Target): Target {
             return null;
         }
 
         // Apply an action, returning true if it was successful
-        apply(battle: Battle, ship: Ship, target: Target): boolean {
-            if (this.canBeUsed(battle, ship)) {
-                target = this.checkTarget(battle, ship, target);
+        apply(ship: Ship, target: Target): boolean {
+            let reject = this.checkCannotBeApplied(ship);
+            if (reject == null) {
+                target = this.checkTarget(ship, target);
                 if (!target && this.needs_target) {
+                    console.warn("Action rejected - no target selected", ship, this, target);
                     return false;
                 }
 
-                let cost = this.getActionPointsUsage(battle, ship, target);
+                let cost = this.getActionPointsUsage(ship, target);
                 if (!ship.useActionPoints(cost)) {
+                    console.warn("Action rejected - not enough power", ship, this, target);
                     return false;
                 }
 
-                this.customApply(battle, ship, target);
+                this.customApply(ship, target);
                 return true;
             } else {
+                console.warn(`Action rejected - ${reject}`, ship, this, target);
                 return false;
             }
         }
 
         // Method to reimplement to apply a action
-        protected customApply(battle: Battle, ship: Ship, target: Target) {
+        protected customApply(ship: Ship, target: Target) {
         }
     }
 }
diff --git a/src/core/actions/DeployDroneAction.spec.ts b/src/core/actions/DeployDroneAction.spec.ts
index bc93ec2..9893c89 100644
--- a/src/core/actions/DeployDroneAction.spec.ts
+++ b/src/core/actions/DeployDroneAction.spec.ts
@@ -20,18 +20,18 @@ module TS.SpaceTac {
             equipment.ap_usage = 0;
             let action = new DeployDroneAction(equipment);
 
-            expect(action.checkTarget(null, ship, new Target(8, 0, null))).toEqual(new Target(8, 0, null));
-            expect(action.checkTarget(null, ship, new Target(12, 0, null))).toEqual(new Target(8, 0, null));
+            expect(action.checkTarget(ship, new Target(8, 0, null))).toEqual(new Target(8, 0, null));
+            expect(action.checkTarget(ship, new Target(12, 0, null))).toEqual(new Target(8, 0, null));
 
             let other = new Ship();
             other.setArenaPosition(8, 0);
-            expect(action.checkTarget(null, ship, new Target(8, 0, other))).toBeNull();
+            expect(action.checkTarget(ship, new Target(8, 0, other))).toBeNull();
         });
 
         it("deploys a new drone", function () {
-            let ship = new Ship();
-            ship.setArenaPosition(0, 0);
             let battle = new Battle();
+            let ship = battle.fleets[0].addShip();
+            ship.setArenaPosition(0, 0);
             battle.playing_ship = ship;
             TestTools.setShipAP(ship, 3);
             let equipment = new Equipment();
@@ -43,7 +43,9 @@ module TS.SpaceTac {
             equipment.target_effects.push(new DamageEffect(50));
             let action = new DeployDroneAction(equipment);
 
-            let result = action.apply(battle, ship, new Target(5, 0, null));
+            battle.log.clear();
+            battle.log.addFilter("value");
+            let result = action.apply(ship, new Target(5, 0, null));
 
             expect(result).toBe(true);
             expect(battle.drones.length).toBe(1);
diff --git a/src/core/actions/DeployDroneAction.ts b/src/core/actions/DeployDroneAction.ts
index a285f14..e403531 100644
--- a/src/core/actions/DeployDroneAction.ts
+++ b/src/core/actions/DeployDroneAction.ts
@@ -9,20 +9,24 @@ module TS.SpaceTac {
             super("deploy-" + equipment.code, "Deploy", true, equipment);
         }
 
-        checkLocationTarget(battle: Battle, ship: Ship, target: Target): Target {
+        checkLocationTarget(ship: Ship, target: Target): Target {
             // TODO Not too close to other ships and drones
             target = target.constraintInRange(ship.arena_x, ship.arena_y, this.equipment.distance);
             return target;
         }
 
-        protected customApply(battle: Battle, ship: Ship, target: Target) {
+        protected customApply(ship: Ship, target: Target) {
             let drone = new Drone(ship, this.equipment.code);
             drone.x = target.x;
             drone.y = target.y;
             drone.radius = this.equipment.blast;
             drone.effects = this.equipment.target_effects;
             drone.duration = this.equipment.duration;
-            battle.addDrone(drone);
+
+            let battle = ship.getBattle();
+            if (battle) {
+                battle.addDrone(drone);
+            }
         }
     }
 }
diff --git a/src/core/actions/EndTurnAction.spec.ts b/src/core/actions/EndTurnAction.spec.ts
index a69b7d5..9920341 100644
--- a/src/core/actions/EndTurnAction.spec.ts
+++ b/src/core/actions/EndTurnAction.spec.ts
@@ -1,14 +1,18 @@
 module TS.SpaceTac.Specs {
     describe("EndTurnAction", () => {
         it("can't be applied to non-playing ship", () => {
+            spyOn(console, "warn").and.stub();
+
             var battle = Battle.newQuickRandom();
             var action = new EndTurnAction();
 
-            expect(action.canBeUsed(battle, battle.play_order[0])).toBe(true);
-            expect(action.canBeUsed(battle, battle.play_order[1])).toBe(false);
+            expect(action.checkCannotBeApplied(battle.play_order[0])).toBe(null);
+            expect(action.checkCannotBeApplied(battle.play_order[1])).toBe("ship not playing");
 
-            var result = action.apply(battle, battle.play_order[1], null);
+            var result = action.apply(battle.play_order[1], null);
             expect(result).toBe(false);
+
+            expect(console.warn).toHaveBeenCalledWith("Action rejected - ship not playing", battle.play_order[1], action, null);
         });
 
         it("ends turn when applied", () => {
@@ -17,7 +21,7 @@ module TS.SpaceTac.Specs {
 
             expect(battle.playing_ship_index).toBe(0);
 
-            var result = action.apply(battle, battle.play_order[0], null);
+            var result = action.apply(battle.play_order[0], null);
             expect(result).toBe(true);
             expect(battle.playing_ship_index).toBe(1);
         });
diff --git a/src/core/actions/EndTurnAction.ts b/src/core/actions/EndTurnAction.ts
index 6a87162..0ce2f46 100644
--- a/src/core/actions/EndTurnAction.ts
+++ b/src/core/actions/EndTurnAction.ts
@@ -5,9 +5,13 @@ module TS.SpaceTac {
             super("endturn", "End ship's turn", false);
         }
 
-        protected customApply(battle: Battle, ship: Ship, target: Target) {
+        protected customApply(ship: Ship, target: Target) {
             ship.endTurn();
-            battle.advanceToNextShip();
+
+            let battle = ship.getBattle();
+            if (battle) {
+                battle.advanceToNextShip();
+            }
         }
     }
 }
diff --git a/src/core/actions/FireWeaponAction.spec.ts b/src/core/actions/FireWeaponAction.spec.ts
index 82e4918..177901c 100644
--- a/src/core/actions/FireWeaponAction.spec.ts
+++ b/src/core/actions/FireWeaponAction.spec.ts
@@ -39,7 +39,7 @@ module TS.SpaceTac {
             battle.playing_ship = ship;
             fleet.setBattle(battle);
 
-            action.apply(battle, ship, Target.newFromLocation(50, 50));
+            action.apply(ship, Target.newFromLocation(50, 50));
             expect(mock_apply).toHaveBeenCalledTimes(1);
             expect(mock_apply).toHaveBeenCalledWith(ship2);
         });
diff --git a/src/core/actions/FireWeaponAction.ts b/src/core/actions/FireWeaponAction.ts
index 19e26f5..1c39189 100644
--- a/src/core/actions/FireWeaponAction.ts
+++ b/src/core/actions/FireWeaponAction.ts
@@ -12,7 +12,7 @@ module TS.SpaceTac {
             this.can_target_space = can_target_space;
         }
 
-        checkLocationTarget(battle: Battle, ship: Ship, target: Target): Target {
+        checkLocationTarget(ship: Ship, target: Target): Target {
             if (this.can_target_space) {
                 target = target.constraintInRange(ship.arena_x, ship.arena_y, this.equipment.distance);
                 return target;
@@ -21,7 +21,7 @@ module TS.SpaceTac {
             }
         }
 
-        checkShipTarget(battle: Battle, ship: Ship, target: Target): Target {
+        checkShipTarget(ship: Ship, target: Target): Target {
             if (ship.getPlayer() === target.ship.getPlayer()) {
                 // No friendly fire
                 return null;
@@ -48,7 +48,7 @@ module TS.SpaceTac {
             return result;
         }
 
-        protected customApply(battle: Battle, ship: Ship, target: Target) {
+        protected customApply(ship: Ship, target: Target) {
             // Face the target
             ship.rotate(Target.newFromShip(ship).getAngleTo(target));
 
@@ -56,7 +56,7 @@ module TS.SpaceTac {
             ship.addBattleEvent(new FireEvent(ship, this.equipment, target));
 
             // Apply effects
-            let effects = this.getEffects(battle, ship, target);
+            let effects = this.getEffects(ship.getBattle(), ship, target);
             effects.forEach(([ship, effect]) => effect.applyOnShip(ship));
         }
     }
diff --git a/src/core/actions/MoveAction.spec.ts b/src/core/actions/MoveAction.spec.ts
index c5a09ee..5cc1563 100644
--- a/src/core/actions/MoveAction.spec.ts
+++ b/src/core/actions/MoveAction.spec.ts
@@ -15,14 +15,14 @@ module TS.SpaceTac {
 
             expect(action.getDistanceByActionPoint(ship)).toBe(0.5);
 
-            var result = action.checkTarget(battle, ship, Target.newFromLocation(0, 2));
+            var result = action.checkTarget(ship, Target.newFromLocation(0, 2));
             expect(result).toEqual(Target.newFromLocation(0, 2));
 
-            result = action.checkTarget(battle, ship, Target.newFromLocation(0, 8));
+            result = action.checkTarget(ship, Target.newFromLocation(0, 8));
             expect(result).toEqual(Target.newFromLocation(0, 3));
 
             ship.values.power.set(0);
-            result = action.checkTarget(battle, ship, Target.newFromLocation(0, 8));
+            result = action.checkTarget(ship, Target.newFromLocation(0, 8));
             expect(result).toBeNull();
         });
 
@@ -31,10 +31,10 @@ module TS.SpaceTac {
             var ship2 = new Ship(null, "Test2");
             var action = new MoveAction(null);
 
-            var result = action.checkTarget(null, ship1, Target.newFromShip(ship1));
+            var result = action.checkTarget(ship1, Target.newFromShip(ship1));
             expect(result).toBeNull();
 
-            result = action.checkTarget(null, ship1, Target.newFromShip(ship2));
+            result = action.checkTarget(ship1, Target.newFromShip(ship2));
             expect(result).toBeNull();
         });
 
@@ -51,13 +51,15 @@ module TS.SpaceTac {
             var action = new MoveAction(engine);
             battle.playing_ship = ship;
 
-            var result = action.apply(battle, ship, Target.newFromLocation(10, 10));
+            spyOn(console, "warn").and.stub();
+
+            var result = action.apply(ship, Target.newFromLocation(10, 10));
             expect(result).toBe(true);
             expect(ship.arena_x).toBeCloseTo(3.535533, 0.00001);
             expect(ship.arena_y).toBeCloseTo(3.535533, 0.00001);
             expect(ship.values.power.get()).toEqual(0);
 
-            result = action.apply(battle, ship, Target.newFromLocation(10, 10));
+            result = action.apply(ship, Target.newFromLocation(10, 10));
             expect(result).toBe(false);
             expect(ship.arena_x).toBeCloseTo(3.535533, 0.00001);
             expect(ship.arena_y).toBeCloseTo(3.535533, 0.00001);
@@ -89,19 +91,19 @@ module TS.SpaceTac {
             var action = new MoveAction(engine);
             action.safety_distance = 2;
 
-            var result = action.checkLocationTarget(battle, ship, Target.newFromLocation(7, 5));
+            var result = action.checkLocationTarget(ship, Target.newFromLocation(7, 5));
             expect(result).toEqual(Target.newFromLocation(7, 5));
 
-            result = action.checkLocationTarget(battle, ship, Target.newFromLocation(8, 5));
+            result = action.checkLocationTarget(ship, Target.newFromLocation(8, 5));
             expect(result).toEqual(Target.newFromLocation(8, 5));
 
-            result = action.checkLocationTarget(battle, ship, Target.newFromLocation(9, 5));
+            result = action.checkLocationTarget(ship, Target.newFromLocation(9, 5));
             expect(result).toEqual(Target.newFromLocation(8, 5));
 
-            result = action.checkLocationTarget(battle, ship, Target.newFromLocation(10, 5));
+            result = action.checkLocationTarget(ship, Target.newFromLocation(10, 5));
             expect(result).toEqual(Target.newFromLocation(8, 5));
 
-            result = action.checkLocationTarget(battle, ship, Target.newFromLocation(12, 5));
+            result = action.checkLocationTarget(ship, Target.newFromLocation(12, 5));
             expect(result).toEqual(Target.newFromLocation(12, 5));
         });
     });
diff --git a/src/core/actions/MoveAction.ts b/src/core/actions/MoveAction.ts
index b8a811d..bef4a05 100644
--- a/src/core/actions/MoveAction.ts
+++ b/src/core/actions/MoveAction.ts
@@ -11,19 +11,24 @@ module TS.SpaceTac {
             this.safety_distance = 50;
         }
 
-        canBeUsed(battle: Battle, ship: Ship, remaining_ap: number = null): boolean {
-            if (battle && battle.playing_ship !== ship) {
-                return false;
+        checkCannotBeApplied(ship: Ship, remaining_ap: number = null): string | null {
+            let base = super.checkCannotBeApplied(ship, Infinity);
+            if (base) {
+                return base;
             }
 
             // Check AP usage
             if (remaining_ap === null) {
                 remaining_ap = ship.values.power.get();
             }
-            return remaining_ap > 0.0001;
+            if (remaining_ap > 0.0001) {
+                return null
+            } else {
+                return "not enough power";
+            }
         }
 
-        getActionPointsUsage(battle: Battle, ship: Ship, target: Target): number {
+        getActionPointsUsage(ship: Ship, target: Target): number {
             if (target === null) {
                 return 0;
             }
@@ -43,23 +48,26 @@ module TS.SpaceTac {
             return this.equipment.distance / this.equipment.ap_usage;
         }
 
-        checkLocationTarget(battle: Battle, ship: Ship, target: Target): Target {
+        checkLocationTarget(ship: Ship, target: Target): Target {
             // Apply maximal distance
             var max_distance = this.getRangeRadius(ship);
             target = target.constraintInRange(ship.arena_x, ship.arena_y, max_distance);
 
             // Apply collision prevention
-            battle.play_order.forEach((iship: Ship) => {
-                if (iship !== ship) {
-                    target = target.moveOutOfCircle(iship.arena_x, iship.arena_y, this.safety_distance,
-                        ship.arena_x, ship.arena_y);
-                }
-            });
+            let battle = ship.getBattle();
+            if (battle) {
+                battle.play_order.forEach((iship: Ship) => {
+                    if (iship !== ship) {
+                        target = target.moveOutOfCircle(iship.arena_x, iship.arena_y, this.safety_distance,
+                            ship.arena_x, ship.arena_y);
+                    }
+                });
+            }
 
             return target;
         }
 
-        protected customApply(battle: Battle, ship: Ship, target: Target) {
+        protected customApply(ship: Ship, target: Target) {
             ship.moveTo(target.x, target.y);
         }
     }
diff --git a/src/core/ai/AIDuel.ts b/src/core/ai/AIDuel.ts
index dfc324c..e1cb6cc 100644
--- a/src/core/ai/AIDuel.ts
+++ b/src/core/ai/AIDuel.ts
@@ -44,14 +44,15 @@ module TS.SpaceTac {
         /**
          * Update the result of a single battle
          */
-        update(winner: AbstractAI | null) {
-            if (winner) {
-                if (winner == this.ai1) {
+        update(winner: number) {
+            if (winner >= 0) {
+                if (winner == 0) {
                     this.win1 += 1;
+                    console.log(` => Player 1 wins (${this.ai1})`);
                 } else {
                     this.win2 += 1;
+                    console.log(` => Player 2 wins (${this.ai2})`);
                 }
-                console.log(` => ${winner.name} wins`);
             } else {
                 this.draw += 1;
                 console.log(" => draw");
@@ -86,9 +87,9 @@ module TS.SpaceTac {
             }
 
             if (battle.ended && !battle.outcome.draw) {
-                this.update(battle.outcome.winner == battle.fleets[0] ? this.ai1 : this.ai2);
+                this.update(battle.fleets.indexOf(battle.outcome.winner));
             } else {
-                this.update(null);
+                this.update(-1);
             }
             if (!this.stopped) {
                 this.scheduled = Timer.global.schedule(100, () => this.next());
diff --git a/src/core/ai/BullyAI.ts b/src/core/ai/BullyAI.ts
index b8eb2a5..d9a31bf 100644
--- a/src/core/ai/BullyAI.ts
+++ b/src/core/ai/BullyAI.ts
@@ -153,7 +153,7 @@ module TS.SpaceTac {
             if (distance > safety_distance) { // Don't move too close
                 target = target.constraintInRange(this.ship.arena_x, this.ship.arena_y,
                     (distance - safety_distance) * APPROACH_FACTOR);
-                target = engine.action.checkLocationTarget(this.ship.getBattle(), this.ship, target);
+                target = engine.action.checkLocationTarget(this.ship, target);
                 return new BullyManeuver(new Maneuver(this.ship, engine, target));
             } else {
                 return null;
diff --git a/src/core/ai/Maneuver.ts b/src/core/ai/Maneuver.ts
index 0a1d8e7..2b7855d 100644
--- a/src/core/ai/Maneuver.ts
+++ b/src/core/ai/Maneuver.ts
@@ -32,8 +32,8 @@ module TS.SpaceTac {
         apply(): void {
             if (this.simulation.success) {
                 this.simulation.parts.forEach(part => {
-                    if (!part.action.apply(this.ship.getBattle(), this.ship, part.target)) {
-                        console.error("AI cannot apply maneuver", this);
+                    if (!part.action.apply(this.ship, part.target)) {
+                        console.error("AI cannot apply maneuver", this, part);
                     }
                 });
             }
diff --git a/src/core/equipments/AbstractWeapon.spec.ts b/src/core/equipments/AbstractWeapon.spec.ts
index fdb5b0f..1ddc88c 100644
--- a/src/core/equipments/AbstractWeapon.spec.ts
+++ b/src/core/equipments/AbstractWeapon.spec.ts
@@ -38,15 +38,15 @@ module TS.SpaceTac.Specs {
 
             weapon.ap_usage = new Range(2);
             var equipment = weapon.generateFixed(0);
-            expect(equipment.action.canBeUsed(null, ship)).toBe(true);
+            expect(equipment.action.checkCannotBeApplied(ship)).toBe(null);
 
             weapon.ap_usage = new Range(3);
             equipment = weapon.generateFixed(0);
-            expect(equipment.action.canBeUsed(null, ship)).toBe(true);
+            expect(equipment.action.checkCannotBeApplied(ship)).toBe(null);
 
             weapon.ap_usage = new Range(4);
             equipment = weapon.generateFixed(0);
-            expect(equipment.action.canBeUsed(null, ship)).toBe(false);
+            expect(equipment.action.checkCannotBeApplied(ship)).toBe("not enough power");
         });
 
         it("can't friendly fire", function () {
@@ -60,9 +60,9 @@ module TS.SpaceTac.Specs {
             weapon.setRange(10, 10);
             var equipment = weapon.generateFixed(0);
 
-            expect(equipment.action.checkShipTarget(null, ship1a, Target.newFromShip(ship2a))).toEqual(
+            expect(equipment.action.checkShipTarget(ship1a, Target.newFromShip(ship2a))).toEqual(
                 Target.newFromShip(ship2a));
-            expect(equipment.action.checkShipTarget(null, ship1a, Target.newFromShip(ship1b))).toBeNull();
+            expect(equipment.action.checkShipTarget(ship1a, Target.newFromShip(ship1b))).toBeNull();
         });
 
         it("can't fire farther than its range", function () {
@@ -78,25 +78,25 @@ module TS.SpaceTac.Specs {
             var equipment = weapon.generateFixed(0);
             expect(equipment.distance).toEqual(10);
 
-            expect(equipment.action.checkLocationTarget(null, ship, Target.newFromLocation(15, 10))).toEqual(
+            expect(equipment.action.checkLocationTarget(ship, Target.newFromLocation(15, 10))).toEqual(
                 Target.newFromLocation(15, 10));
-            expect(equipment.action.checkLocationTarget(null, ship, Target.newFromLocation(30, 10))).toEqual(
+            expect(equipment.action.checkLocationTarget(ship, Target.newFromLocation(30, 10))).toEqual(
                 Target.newFromLocation(20, 10));
 
             // Ship targetting
             var ship2 = new Ship(fleet2);
 
             ship2.setArenaPosition(10, 15);
-            expect(equipment.action.checkShipTarget(null, ship, Target.newFromShip(ship2))).toEqual(
+            expect(equipment.action.checkShipTarget(ship, Target.newFromShip(ship2))).toEqual(
                 Target.newFromShip(ship2));
 
             ship2.setArenaPosition(10, 25);
-            expect(equipment.action.checkShipTarget(null, ship, Target.newFromShip(ship2))).toBeNull();
+            expect(equipment.action.checkShipTarget(ship, Target.newFromShip(ship2))).toBeNull();
 
             // Forbid targetting in space
             weapon.setRange(10, 10, false);
             equipment = weapon.generateFixed(0);
-            expect(equipment.action.checkLocationTarget(null, ship, Target.newFromLocation(15, 10))).toBeNull();
+            expect(equipment.action.checkLocationTarget(ship, Target.newFromLocation(15, 10))).toBeNull();
         });
 
         it("can target an enemy ship and damage it", function () {
@@ -119,17 +119,17 @@ module TS.SpaceTac.Specs {
 
             var equipment = weapon.generateFixed(0);
 
-            equipment.action.apply(null, ship1, Target.newFromShip(ship2));
+            equipment.action.apply(ship1, Target.newFromShip(ship2));
             expect(ship2.values.hull.get()).toEqual(100);
             expect(ship2.values.shield.get()).toEqual(10);
             expect(ship1.values.power.get()).toEqual(49);
 
-            equipment.action.apply(null, ship1, Target.newFromShip(ship2));
+            equipment.action.apply(ship1, Target.newFromShip(ship2));
             expect(ship2.values.hull.get()).toEqual(90);
             expect(ship2.values.shield.get()).toEqual(0);
             expect(ship1.values.power.get()).toEqual(48);
 
-            equipment.action.apply(null, ship1, Target.newFromShip(ship2));
+            equipment.action.apply(ship1, Target.newFromShip(ship2));
             expect(ship2.values.hull.get()).toEqual(70);
             expect(ship2.values.shield.get()).toEqual(0);
             expect(ship1.values.power.get()).toEqual(47);
diff --git a/src/core/equipments/PowerDepleter.spec.ts b/src/core/equipments/PowerDepleter.spec.ts
index f8dc971..b5757d7 100644
--- a/src/core/equipments/PowerDepleter.spec.ts
+++ b/src/core/equipments/PowerDepleter.spec.ts
@@ -13,7 +13,7 @@ module TS.SpaceTac.Specs {
             expect(target.sticky_effects).toEqual([]);
 
             // Attribute is immediately limited
-            equipment.action.apply(null, ship, Target.newFromShip(target));
+            equipment.action.apply(ship, Target.newFromShip(target));
 
             expect(target.values.power.get()).toBe(4);
             expect(target.sticky_effects).toEqual([
diff --git a/src/core/equipments/RepairDrone.spec.ts b/src/core/equipments/RepairDrone.spec.ts
index eaa8647..7840dee 100644
--- a/src/core/equipments/RepairDrone.spec.ts
+++ b/src/core/equipments/RepairDrone.spec.ts
@@ -7,10 +7,10 @@ module TS.SpaceTac.Equipments {
             expect(equipment.target_effects).toEqual([new ValueEffect("hull", 30)]);
 
             let battle = new Battle();
-            let ship = new Ship();
+            let ship = battle.fleets[0].addShip();
             battle.playing_ship = ship;
             TestTools.setShipAP(ship, 10);
-            let result = equipment.action.apply(battle, ship, new Target(5, 5, null));
+            let result = equipment.action.apply(ship, new Target(5, 5, null));
             expect(result).toBe(true);
 
             expect(battle.drones.length).toBe(1);
diff --git a/src/core/equipments/SubMunitionMissile.spec.ts b/src/core/equipments/SubMunitionMissile.spec.ts
index 2a4b2a5..a14ceaa 100644
--- a/src/core/equipments/SubMunitionMissile.spec.ts
+++ b/src/core/equipments/SubMunitionMissile.spec.ts
@@ -34,12 +34,12 @@ module TS.SpaceTac.Specs {
             battle.log.addFilter("value");
 
             // Fire at a ship
-            var t = Target.newFromShip(enemy1);
-            expect(equipment.action.canBeUsed(battle, ship)).toBe(true);
-            equipment.action.apply(battle, ship, t);
+            var target = Target.newFromShip(enemy1);
+            expect(equipment.action.checkCannotBeApplied(ship)).toBe(null);
+            equipment.action.apply(ship, target);
             checkHP(50, 10, 50, 10, 50, 10);
             expect(battle.log.events.length).toBe(4);
-            expect(battle.log.events[0]).toEqual(new FireEvent(ship, equipment, t));
+            expect(battle.log.events[0]).toEqual(new FireEvent(ship, equipment, target));
             expect(battle.log.events[1]).toEqual(new DamageEvent(ship, 0, 20));
             expect(battle.log.events[2]).toEqual(new DamageEvent(enemy1, 0, 20));
             expect(battle.log.events[3]).toEqual(new DamageEvent(enemy2, 0, 20));
@@ -47,24 +47,24 @@ module TS.SpaceTac.Specs {
             battle.log.clear();
 
             // Fire in space
-            t = Target.newFromLocation(2.4, 0);
-            expect(equipment.action.canBeUsed(battle, ship)).toBe(true);
-            equipment.action.apply(battle, ship, t);
+            target = Target.newFromLocation(2.4, 0);
+            expect(equipment.action.checkCannotBeApplied(ship)).toBe(null);
+            equipment.action.apply(ship, target);
             checkHP(50, 10, 40, 0, 40, 0);
             expect(battle.log.events.length).toBe(3);
-            expect(battle.log.events[0]).toEqual(new FireEvent(ship, equipment, t));
+            expect(battle.log.events[0]).toEqual(new FireEvent(ship, equipment, target));
             expect(battle.log.events[1]).toEqual(new DamageEvent(enemy1, 10, 10));
             expect(battle.log.events[2]).toEqual(new DamageEvent(enemy2, 10, 10));
 
             battle.log.clear();
 
             // Fire far away
-            t = Target.newFromLocation(5, 0);
-            expect(equipment.action.canBeUsed(battle, ship)).toBe(true);
-            equipment.action.apply(battle, ship, t);
+            target = Target.newFromLocation(5, 0);
+            expect(equipment.action.checkCannotBeApplied(ship)).toBe(null);
+            equipment.action.apply(ship, target);
             checkHP(50, 10, 40, 0, 40, 0);
             expect(battle.log.events.length).toBe(1);
-            expect(battle.log.events[0]).toEqual(new FireEvent(ship, equipment, t));
+            expect(battle.log.events[0]).toEqual(new FireEvent(ship, equipment, target));
         });
     });
 }
diff --git a/src/ui/battle/ActionIcon.ts b/src/ui/battle/ActionIcon.ts
index 2b88a2f..4b3d4d1 100644
--- a/src/ui/battle/ActionIcon.ts
+++ b/src/ui/battle/ActionIcon.ts
@@ -88,7 +88,7 @@ module TS.SpaceTac.UI {
             if (!this.bar.interactive) {
                 return;
             }
-            if (!this.action.canBeUsed(this.battleview.battle, this.ship)) {
+            if (this.action.checkCannotBeApplied(this.ship)) {
                 return;
             }
             if (this.selected) {
@@ -104,7 +104,7 @@ module TS.SpaceTac.UI {
             this.battleview.arena.range_hint.setPrimary(this.ship, this.action);
 
             // Update fading statuses
-            this.bar.updateSelectedActionPower(this.action.getActionPointsUsage(this.battleview.battle, this.ship, null));
+            this.bar.updateSelectedActionPower(this.action.getActionPointsUsage(this.ship, null));
 
             // Set the selected state
             this.setSelected(true);
@@ -127,14 +127,14 @@ module TS.SpaceTac.UI {
         // Called when a target is hovered
         //  This will check the target against current action and adjust it if needed
         processHover(target: Target): void {
-            target = this.action.checkTarget(this.battleview.battle, this.ship, target);
+            target = this.action.checkTarget(this.ship, target);
             this.targetting.setTarget(target, false, this.action.getBlastRadius(this.ship));
-            this.bar.updateSelectedActionPower(this.action.getActionPointsUsage(this.battleview.battle, this.ship, target));
+            this.bar.updateSelectedActionPower(this.action.getActionPointsUsage(this.ship, target));
         }
 
         // Called when a target is selected
         processSelection(target: Target): void {
-            if (this.action.apply(this.battleview.battle, this.ship, target)) {
+            if (this.action.apply(this.ship, target)) {
                 this.bar.actionEnded();
             }
         }
@@ -159,7 +159,7 @@ module TS.SpaceTac.UI {
         // Update the active status, from the action canBeUsed result
         updateActiveStatus(force = false): void {
             var old_active = this.active;
-            this.active = this.action.canBeUsed(this.battleview.battle, this.ship);
+            this.active = !this.action.checkCannotBeApplied(this.ship);
             if (force || (this.active != old_active)) {
                 Animation.setVisibility(this.game, this.layer_active, this.active, 500);
                 this.game.tweens.create(this.layer_icon).to({ alpha: this.active ? 1 : 0.3 }, 500).start();
@@ -170,7 +170,7 @@ module TS.SpaceTac.UI {
         // Update the fading status, given an hypothetical remaining AP
         updateFadingStatus(remaining_ap: number): void {
             var old_fading = this.fading;
-            this.fading = this.active && !this.action.canBeUsed(this.battleview.battle, this.ship, remaining_ap);
+            this.fading = this.active && (this.action.checkCannotBeApplied(this.ship, remaining_ap) != null);
             if (this.fading != old_fading) {
                 Animation.setVisibility(this.game, this.layer_active, this.active && !this.fading, 500);
             }