Okay, some people may know this, here's what it is. A giant apple is sitting in the middle of nowhere, and there's a UFO inside of it. Here's how to get to it.

Go to Operation Little Saturn. You should be in a tank, at the beginning of the level, turn around. There should be a dead tree all alone. Try climbing up the hill on it's right. You should get up. Follow the road to the left. Don't fall off the mountain, keep going. In the distance after awhile, you'll see a big apple. Keep going until you get inside. Then you'll see the UFO.

On cheats menu in extras put r2 r1 l1 l2 left down right up []

At the level select screen hold, up on controller two and on controller one press
Start, select, select, square.

(Note: You'll need two controllers to enter this code.) Select "Single Player" mode and enter your players name. When the level-select screen appears, hold UP on controller 2 and press START, SELECT, SELECT, SQUARE on controller 1 to unlock all levels.

On the level screen hold, up on controller two and then press start, select, select, and square on controller one

First ,you need two controllers plugged in.
Press and hold up on controller two, then press START, SELECT, SELECT and SQUARE. All the levels for the Eastern front, North Africa and the Western Front should now be avaliable.