Press the 1 key to be player 1, and the 2 key to be player 2. Press the arrow keys to move and the space bar to fire. If you destroy the light cruiser, you will win! (there may be a special cheat that gives you reinforcements) Instead of multiplayer, if you can't, you can switch back and forth between the two ships. Press "b" for bomb, and 'R' for reinforcements.
