Four of their ships sit at the bottom of the Pacific Ocean, raising sea levels continuously for 5 years until almost 88% of the surface is submerged.

In order to effectively fight the aliens, the fictional Earth Ocean Alliance develops the "Hydras", one-man submarine fighter craft.

The objective is to travel through the alien-infested seas and fend off the targets long enough to complete the missions.

However, the player is trapped inside one of the vessels, and his fate is uncertain as the game concludes.

As in Rainbow Studios' other rail shooters The Hive and Ravage D.C.X., the player shoots targets that appear as live sprites in front of a full-motion video background.