Enable "Cheat mode" and shoot the men in the room, then get on to the walkway. Go through the door by the box. Shoot the man on the little crate moving machine. Enable the god code, then jump down onto the ground. Run through the gap to the left as if you were still in the machine. Now, run past all the towers to your left. You should see a cargo ship. Run past it. It may appear like a dead end, but keep running and you will appear by the ship with the Boss on it. Enable the jump 10 code to fly over the fence. Enter the ship and kill the boss to finish the level.