The object of the game is to defend the buildings at the bottom of the screen.
There are four types of attack ships that move at the bottom of the screen. You move just above the buildings. Enemies will drop bombs and try to damage the buildings or destroy you. You must fire missiles to destroy them. The waves of enemies never stop.
The game ends when your three ships are destroyed or the two buildings are damaged enough to collapse.
There are eight variations of the game. Some have the ship moving sideways as it moves downward, some have the shot moving sideways as it does so, some are faster, and some are a combination of some or all of these.
