In the Zeppelin level if you are playing with at least two players, when one player is in the bomb release room, go on the place where there is a low Armor and make sure that they are facing the trap door and shoot that player. He/She will get pushed and it looks like they will land on the trap door but they go through it as if it was open and fall to the water. To make the other player not die fast make sure handicap is on and use a Shotgun too. Also make the other player aligned with the middle of the door.