When you get to the part in the Tactical Decisions level where you have to disable the electric fence, knock the person out then destroy it. When done, hold Circle to exit. After that, go to the electric fence and slash open the first one. Jump on the other side and slash the last three. Once you are done with that, turn around and the background should turn white. You can only see the airplane, yourself, and the electric fence. You also cannot go any farther. To exit out of this, jump back over the fence. Walk towards the gun machine then continue the game.