diff --git a/aircraft_cmd.c b/aircraft_cmd.c
index 54b8815378..fd7dad834b 100644
--- a/aircraft_cmd.c
+++ b/aircraft_cmd.c
@@ -158,7 +158,7 @@ static int32 EstimateAircraftCost(EngineID engine_type)
 /** Build an aircraft.
  * @param tile tile of depot where aircraft is built
  * @param p1 aircraft type being built (engine)
- * @param p2 unused
+ * @param p2 bit 0 when set, the unitnumber will be 0, otherwise it will be a free number
  */
 int32 CmdBuildAircraft(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 {
@@ -186,7 +186,7 @@ int32 CmdBuildAircraft(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 		return_cmd_error(STR_00E1_TOO_MANY_VEHICLES_IN_GAME);
 	}
 
-	unit_num = GetFreeUnitNumber(VEH_Aircraft);
+	unit_num = (HASBIT(p2, 0) == true) ? 0 : GetFreeUnitNumber(VEH_Aircraft);
 	if (unit_num > _patches.max_aircraft)
 		return_cmd_error(STR_00E1_TOO_MANY_VEHICLES_IN_GAME);
 
diff --git a/roadveh_cmd.c b/roadveh_cmd.c
index c9d1176f85..963f635ecb 100644
--- a/roadveh_cmd.c
+++ b/roadveh_cmd.c
@@ -103,7 +103,7 @@ static int32 EstimateRoadVehCost(EngineID engine_type)
 /** Build a road vehicle.
  * @param tile tile of depot where road vehicle is built
  * @param p1 bus/truck type being built (engine)
- * @param p2 unused
+ * @param p2 bit 0 when set, the unitnumber will be 0, otherwise it will be a free number
  */
 int32 CmdBuildRoadVeh(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 {
@@ -129,7 +129,7 @@ int32 CmdBuildRoadVeh(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 		return_cmd_error(STR_00E1_TOO_MANY_VEHICLES_IN_GAME);
 
 	/* find the first free roadveh id */
-	unit_num = GetFreeUnitNumber(VEH_Road);
+	unit_num = (HASBIT(p2, 0) == true) ? 0 : GetFreeUnitNumber(VEH_Road);
 	if (unit_num > _patches.max_roadveh)
 		return_cmd_error(STR_00E1_TOO_MANY_VEHICLES_IN_GAME);
 
diff --git a/ship_cmd.c b/ship_cmd.c
index 3cb66e4304..1d6e1383d6 100644
--- a/ship_cmd.c
+++ b/ship_cmd.c
@@ -811,7 +811,7 @@ void ShipsYearlyLoop(void)
 /** Build a ship.
  * @param tile tile of depot where ship is built
  * @param p1 ship type being built (engine)
- * @param p2 unused
+ * @param p2 bit 0 when set, the unitnumber will be 0, otherwise it will be a free number
  */
 int32 CmdBuildShip(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 {
@@ -833,8 +833,9 @@ int32 CmdBuildShip(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 	if (!IsTileOwner(tile, _current_player)) return CMD_ERROR;
 
 	v = AllocateVehicle();
-	if (v == NULL || IsOrderPoolFull() ||
-			(unit_num = GetFreeUnitNumber(VEH_Ship)) > _patches.max_ships)
+	unit_num = (HASBIT(p2, 0) == true) ? 0 : GetFreeUnitNumber(VEH_Ship);
+
+	if (v == NULL || IsOrderPoolFull() || unit_num > _patches.max_ships)
 		return_cmd_error(STR_00E1_TOO_MANY_VEHICLES_IN_GAME);
 
 	if (flags & DC_EXEC) {
diff --git a/train_cmd.c b/train_cmd.c
index 81cccfc04e..35f5d41afe 100644
--- a/train_cmd.c
+++ b/train_cmd.c
@@ -699,8 +699,8 @@ static void AddRearEngineToMultiheadedTrain(Vehicle* v, Vehicle* u, bool buildin
 /** Build a railroad vehicle.
  * @param tile tile of the depot where rail-vehicle is built
  * @param p1 engine type id
- * @param p2 bit 0 prevents any free cars from being added to the train
- *           bit 1 when set, the train will get number 0, otherwise it will get a free number
+ * @param p2 bit 0 when set, the train will get number 0, otherwise it will get a free number
+ *           bit 1 prevents any free cars from being added to the train
  */
 int32 CmdBuildRailVehicle(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 {
@@ -744,14 +744,10 @@ int32 CmdBuildRailVehicle(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 
 		v = vl[0];
 
-		if (HASBIT(p2, 1)) {
-			// no number is needed, so we assign 0. The engine is likely intended for a train with more than one engine
-			unit_num = 0;
-		} else {
-			unit_num = GetFreeUnitNumber(VEH_Train);
-			if (unit_num > _patches.max_trains)
-				return_cmd_error(STR_00E1_TOO_MANY_VEHICLES_IN_GAME);
-		}
+		unit_num = (HASBIT(p2, 0) == true) ? 0 : GetFreeUnitNumber(VEH_Train);
+		if (unit_num > _patches.max_trains)
+			return_cmd_error(STR_00E1_TOO_MANY_VEHICLES_IN_GAME);
+
 		if (flags & DC_EXEC) {
 			DiagDirection dir = GetRailDepotDirection(tile);
 			int x = TileX(tile) * TILE_SIZE + _vehicle_initial_x_fract[dir];
@@ -815,7 +811,7 @@ int32 CmdBuildRailVehicle(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 			TrainConsistChanged(v);
 			UpdateTrainAcceleration(v);
 
-			if (!HASBIT(p2, 0)) {	// check if the cars should be added to the new vehicle
+			if (!HASBIT(p2, 1)) {	// check if the cars should be added to the new vehicle
 				NormalizeTrainVehInDepot(v);
 			}
 
diff --git a/vehicle.c b/vehicle.c
index 9404a6db29..3d11030140 100644
--- a/vehicle.c
+++ b/vehicle.c
@@ -1490,7 +1490,7 @@ int32 CmdCloneVehicle(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 	Vehicle *v_front, *v;
 	Vehicle *w_front, *w, *w_rear;
 	int cost, total_cost = 0;
-	uint32 build_argument = 1;
+	uint32 build_argument = 2;
 
 	if (!IsVehicleIndex(p1)) return CMD_ERROR;
 	v = GetVehicle(p1);
@@ -1624,7 +1624,7 @@ static int32 ReplaceVehicle(Vehicle **w, byte flags)
 	new_engine_type = EngineReplacementForPlayer(p, old_v->engine_type);
 	if (new_engine_type == INVALID_ENGINE) new_engine_type = old_v->engine_type;
 
-	cost = DoCommand(old_v->tile, new_engine_type, 1, flags, CMD_BUILD_VEH(old_v->type));
+	cost = DoCommand(old_v->tile, new_engine_type, 3, flags, CMD_BUILD_VEH(old_v->type));
 	if (CmdFailed(cost)) return cost;
 
 	if (flags & DC_EXEC) {
@@ -1660,6 +1660,7 @@ static int32 ReplaceVehicle(Vehicle **w, byte flags)
 			new_v->profit_last_year = old_v->profit_last_year;
 			new_v->service_interval = old_v->service_interval;
 			new_front = true;
+			new_v->unitnumber = old_v->unitnumber;	// use the same unit number
 
 			new_v->current_order = old_v->current_order;
 			if (old_v->type == VEH_Train && GetNextVehicle(old_v) != NULL){