Go to the cheat menu in extras menu and enter the following

Beat the game on certain difficulties to unlock these cheats:

At the beginning of Operation Little Saturn, in the Russian campaign (it's one of the tank levels), turn immediately to your left and find a single tree sitting on the slope of the embankment that doubles as the level's collision wall. Drive up the embankment directly to the right of the tree and right through the level's collision wall. From here turn to your left and locate a road that follows around the mountain away from the rest of the level. Continue down the road and in about 30 seconds to a minute to should see a large red apple in the distance. Continue driving into the apple to find one of the strangest thing I've ever found in a WWII game... Besides a 20 story giant red apple, at least.

In the level where you enter the undergound tunnels to blow up the ladders, start by going down the spiral staircase to dispose of the germans. Then enter the room to the right. There is a small alcove on the right side of this room. Throw a couple of grenades into the alcove, then examine the door and throw one more grenade into it. The explosion Will reveal this VERY CREEPY room.

This room is located in the second British level. At the end, after you have blown up the fuel depot, There will be two old looking buildings by the mountain-dead end. The one at the left that looks like a church or 3 loafs of bread put together. The door on the right has the Sultan's room. Don't go to the smaller building to the right. Throw 2 sticky grenades on the door, then examine it. After that, throw 2 more sticky grenades on it, and whatch it explode to reveal a hidden stair case. Go down it to find an Arabic guy playing an old guitar thing. You can get a health pack here also.

This one is in the American sewer level where you have to blow up the ladders. At the end of the level where you see the whole and brick wall, and are still in the tunnels, go to the second alcove to the right going backwards from the whole. You will see a tunnel behind the boards. Just blow them up with a couple of grenades. Then go down the tunnel, and you will be at the dance party with some familar characters. You can pick up a Browing 50. cal here, and you can scratch on the record players. Just go up to them behind the table with the German, and you will see a radio symbol.