Fortress

Fortress is a 1-player arcade game for the Apple II.

Earth is under attack. You are the Commander of the last surviving Star Fortress in the Mars defense line. The fortress is armed four laser cannons which can fire in the 4 cardinal directions, as well as a limited supply of Smart Bombs, which can destroy every enemy on the screen. Enemy ships attack in progressively more difficult waves, with faster ships appearing in later waves. If the fortress is hit, it's game over.