Space Fortress

Space Fortress is a fixed screen space-themed shooting arcade game with three stages. But unlike in most multi-stage games, each stage continues indefinitely until you lose a life.

Stage one has similar gameplay to Asteroids , with your craft in the middle of the screen trying to avoid hordes of alien vessels and control using the joystick for left and right as well as fire and thrust buttons. During this stage, in addition to the hunters and bombers, a gravity bomb may appear which will pull your vessel towards it and detonate on contact. Maneuvering costs fuel, but this is replenished every time you destroy a gravity bomb.

Once this ship is destroyed, you are next tasked with defending a large spaceship from various attacking enemies, mostly killers and drones. If your ship is hit, or if the large ship is sufficiently damaged by multiple hits, this stage ends and you are taken to the last stage. Here you are defending a ground-base from attacking aliens as you move back and forwards across the surface. If an alien strikes the base, it will incur damage that is slowly repaired. But if the base is too badly damaged, it is game over.