diff --git a/src/disaster_cmd.cpp b/src/disaster_cmd.cpp
--- a/src/disaster_cmd.cpp
+++ b/src/disaster_cmd.cpp
@@ -607,7 +607,7 @@ static void DisasterTick_Big_Ufo(Vehicle
 		}
 
 		InitializeDisasterVehicle(u, -6 * TILE_SIZE, v->y_pos, 135, DIR_SW, ST_Big_Ufo_Destroyer);
-		u->u.disaster.unk2 = v->index;
+		u->u.disaster.big_ufo_destroyer_target = v->index;
 
 		w = ForceAllocateSpecialVehicle();
 		if (w == NULL) return;
@@ -667,7 +667,7 @@ static void DisasterTick_Big_Ufo_Destroy
 	}
 
 	if (v->current_order.dest == 0) {
-		u = GetVehicle(v->u.disaster.unk2);
+		u = GetVehicle(v->u.disaster.big_ufo_destroyer_target);
 		if (delta(v->x_pos, u->x_pos) > TILE_SIZE) return;
 		v->current_order.dest = 1;
 
diff --git a/src/industry_cmd.cpp b/src/industry_cmd.cpp
--- a/src/industry_cmd.cpp
+++ b/src/industry_cmd.cpp
@@ -696,7 +696,7 @@ static void TileLoopIndustry_BubbleGener
 		EV_BUBBLE
 	);
 
-	if (v != NULL) v->u.special.unk2 = dir;
+	if (v != NULL) v->u.special.animation_substate = dir;
 }
 
 static void TileLoop_Industry(TileIndex tile)
diff --git a/src/oldloader.cpp b/src/oldloader.cpp
--- a/src/oldloader.cpp
+++ b/src/oldloader.cpp
@@ -1053,8 +1053,8 @@ static const OldChunks vehicle_air_chunk
 };
 
 static const OldChunks vehicle_special_chunk[] = {
-	OCL_SVAR( OC_UINT16, VehicleSpecial, unk0 ),
-	OCL_SVAR(  OC_UINT8, VehicleSpecial, unk2 ),
+	OCL_SVAR( OC_UINT16, VehicleSpecial, animation_state ),
+	OCL_SVAR(  OC_UINT8, VehicleSpecial, animation_substate ),
 
 	OCL_NULL( 7 ), // Junk
 
@@ -1063,7 +1063,7 @@ static const OldChunks vehicle_special_c
 
 static const OldChunks vehicle_disaster_chunk[] = {
 	OCL_SVAR( OC_UINT16, VehicleDisaster, image_override ),
-	OCL_SVAR( OC_UINT16, VehicleDisaster, unk2 ),
+	OCL_SVAR( OC_UINT16, VehicleDisaster, big_ufo_destroyer_target ),
 
 	OCL_NULL( 6 ), ///< Junk
 
diff --git a/src/roadveh_cmd.cpp b/src/roadveh_cmd.cpp
--- a/src/roadveh_cmd.cpp
+++ b/src/roadveh_cmd.cpp
@@ -737,7 +737,7 @@ static void HandleBrokenRoadVeh(Vehicle 
 
 		if (!(v->vehstatus & VS_HIDDEN)) {
 			Vehicle *u = CreateEffectVehicleRel(v, 4, 4, 5, EV_BREAKDOWN_SMOKE);
-			if (u != NULL) u->u.special.unk0 = v->breakdown_delay * 2;
+			if (u != NULL) u->u.special.animation_state = v->breakdown_delay * 2;
 		}
 	}
 
diff --git a/src/ship_cmd.cpp b/src/ship_cmd.cpp
--- a/src/ship_cmd.cpp
+++ b/src/ship_cmd.cpp
@@ -220,7 +220,7 @@ static void HandleBrokenShip(Vehicle *v)
 
 		if (!(v->vehstatus & VS_HIDDEN)) {
 			Vehicle *u = CreateEffectVehicleRel(v, 4, 4, 5, EV_BREAKDOWN_SMOKE);
-			if (u != NULL) u->u.special.unk0 = v->breakdown_delay * 2;
+			if (u != NULL) u->u.special.animation_state = v->breakdown_delay * 2;
 		}
 	}
 
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -3138,7 +3138,7 @@ static void HandleBrokenTrain(Vehicle *v
 
 		if (!(v->vehstatus & VS_HIDDEN)) {
 			Vehicle *u = CreateEffectVehicleRel(v, 4, 4, 5, EV_BREAKDOWN_SMOKE);
-			if (u != NULL) u->u.special.unk0 = v->breakdown_delay * 2;
+			if (u != NULL) u->u.special.animation_state = v->breakdown_delay * 2;
 		}
 	}
 
diff --git a/src/vehicle.cpp b/src/vehicle.cpp
--- a/src/vehicle.cpp
+++ b/src/vehicle.cpp
@@ -1113,8 +1113,8 @@ static void BreakdownSmokeTick(Vehicle *
 		EndVehicleMove(v);
 	}
 
-	v->u.special.unk0--;
-	if (v->u.special.unk0 == 0) {
+	v->u.special.animation_state--;
+	if (v->u.special.animation_state == 0) {
 		BeginVehicleMove(v);
 		EndVehicleMove(v);
 		DeleteVehicle(v);
@@ -1147,8 +1147,8 @@ static void BulldozerInit(Vehicle *v)
 {
 	v->cur_image = SPR_BULLDOZER_NE;
 	v->progress = 0;
-	v->u.special.unk0 = 0;
-	v->u.special.unk2 = 0;
+	v->u.special.animation_state = 0;
+	v->u.special.animation_substate = 0;
 }
 
 struct BulldozerMovement {
@@ -1194,7 +1194,7 @@ static void BulldozerTick(Vehicle *v)
 {
 	v->progress++;
 	if ((v->progress & 7) == 0) {
-		const BulldozerMovement* b = &_bulldozer_movement[v->u.special.unk0];
+		const BulldozerMovement* b = &_bulldozer_movement[v->u.special.animation_state];
 
 		BeginVehicleMove(v);
 
@@ -1203,11 +1203,11 @@ static void BulldozerTick(Vehicle *v)
 		v->x_pos += _inc_by_dir[b->direction].x;
 		v->y_pos += _inc_by_dir[b->direction].y;
 
-		v->u.special.unk2++;
-		if (v->u.special.unk2 >= b->duration) {
-			v->u.special.unk2 = 0;
-			v->u.special.unk0++;
-			if (v->u.special.unk0 == lengthof(_bulldozer_movement)) {
+		v->u.special.animation_substate++;
+		if (v->u.special.animation_substate >= b->duration) {
+			v->u.special.animation_substate = 0;
+			v->u.special.animation_state++;
+			if (v->u.special.animation_state == lengthof(_bulldozer_movement)) {
 				EndVehicleMove(v);
 				DeleteVehicle(v);
 				return;
@@ -1399,7 +1399,7 @@ static void BubbleTick(Vehicle *v)
 			EndVehicleMove(v);
 			return;
 		}
-		if (v->u.special.unk2 != 0) {
+		if (v->u.special.animation_substate != 0) {
 			v->spritenum = GB(InteractiveRandom(), 0, 2) + 1;
 		} else {
 			v->spritenum = 6;
@@ -3042,8 +3042,8 @@ static const SaveLoad _special_desc[] = 
 	    SLE_VAR(Vehicle, progress,      SLE_UINT8),
 	    SLE_VAR(Vehicle, vehstatus,     SLE_UINT8),
 
-	    SLE_VARX(cpp_offsetof(Vehicle, u) + cpp_offsetof(VehicleSpecial, unk0), SLE_UINT16),
-	    SLE_VARX(cpp_offsetof(Vehicle, u) + cpp_offsetof(VehicleSpecial, unk2), SLE_UINT8),
+	    SLE_VARX(cpp_offsetof(Vehicle, u) + cpp_offsetof(VehicleSpecial, animation_state),    SLE_UINT16),
+	    SLE_VARX(cpp_offsetof(Vehicle, u) + cpp_offsetof(VehicleSpecial, animation_substate), SLE_UINT8),
 
 	/* reserve extra space in savegame here. (currently 16 bytes) */
 	SLE_CONDNULL(16, 2, SL_MAX_VERSION),
@@ -3080,8 +3080,8 @@ static const SaveLoad _disaster_desc[] =
 	SLE_CONDVAR(Vehicle, age,           SLE_INT32,                  31, SL_MAX_VERSION),
 	    SLE_VAR(Vehicle, tick_counter,  SLE_UINT8),
 
-	   SLE_VARX(cpp_offsetof(Vehicle, u) + cpp_offsetof(VehicleDisaster, image_override), SLE_UINT16),
-	   SLE_VARX(cpp_offsetof(Vehicle, u) + cpp_offsetof(VehicleDisaster, unk2),           SLE_UINT16),
+	   SLE_VARX(cpp_offsetof(Vehicle, u) + cpp_offsetof(VehicleDisaster, image_override),           SLE_UINT16),
+	   SLE_VARX(cpp_offsetof(Vehicle, u) + cpp_offsetof(VehicleDisaster, big_ufo_destroyer_target), SLE_UINT16),
 
 	/* reserve extra space in savegame here. (currently 16 bytes) */
 	SLE_CONDNULL(16,                                                 2, SL_MAX_VERSION),
diff --git a/src/vehicle.h b/src/vehicle.h
--- a/src/vehicle.h
+++ b/src/vehicle.h
@@ -202,13 +202,13 @@ struct VehicleRoad {
 };
 
 struct VehicleSpecial {
-	uint16 unk0;
-	byte unk2;
+	uint16 animation_state;
+	byte animation_substate;
 };
 
 struct VehicleDisaster {
 	uint16 image_override;
-	uint16 unk2;
+	VehicleID big_ufo_destroyer_target;
 };
 
 struct VehicleShip {