Released on the Arcades as Space Zap and for the Bally Astrocade as Space Fortress.
This is a fixed screen shoot 'em up where the player is in control of a stationary laser base which is located in the middle of the screen.
Alien space ships will appear from the four sides of the screen and launch space mines towards the laser base. The player's task is simply to shoot them down before they reach and destroy the laser base.
The game is controlled with five buttons: one for shooting and four for aiming, one for each direction.
In addition to the mines and alien ships there are also attack satellites that orbit the laser base before attacking. The mines are worth 250 points, alien ships are worth 500 points and attack satellites are worth 2,000 points. The player starts out with three lives but earns a new one at 75,000, 150,000 and 300,000 points.