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The player takes on the role of the last remaining fighter left to save Earth from an alien invasion in the role of one of Earth's elite "hydrofighter" pilots. Five years have passed since the aliens broke through Earth's defenses and set up their ocean bases. The player's objective is to travel through the alien-infested seas and try to destroy the alien presence there.
The player is tasked with operating weapons on a moving submarine-type ship, fighting an alien race which has attacked and controls the Earth's seas.
There are also some levels where the player goes on foot moving throughout the bases and sunken ships.