Atlantis 1982 By: Imagic

Overview:

In the game Atlantis, you control three cannons, strategically placed left, center and right of the screen. You must protect the underwater civilization from surface dwellers attacking from the skies with planes and jets. These attackers are attempting to destroy your underwater cities and their power generators.
This game features colorful graphics and quick paced gameplay. Controls respond well, but you are only able to fire two shots at a time, so they must be timed properly. The sound library features your gun firing and explosions, as well a bell denoting a cleared attack wave. This game is not overly glamorous, but it plays well and provides a good challenge.

Directions:

Protect the fabled underworld of Atlantis from attackers from the sky. Planes fly across the screen from both sides, progressively dropping altitude with each screen pass. When the attackers reach the level above the water, they attack with a beam that destroys whatever it hits.  

Your three weapons have fixed aim. The two outermost weapons fire diagonally to the opposite corner of the screen. The center gun fires straight up and is always their first target. The flanking cannons are never fired upon. After the center gun is destroyed, planes attempt to destroy three underwater cities and three power generators. When those six items have been destroyed, the game is over. The center gun is replaced after an attack wave, but any other losses are permanent.