You must guide your submarine through the underwater caverns, avoiding or destroying the various adversaries which come your way by use of your front located cannon or the bombs you can drop down in front of you.

These take the form of enemy missiles, bases, surface ships, fish and underwater spiders! The surface ships drop dozens of depthcharges onto your position, which must be avoided. There are occasions when of course, this proves to be impossible. Three ships on the surface scattering the playfield with depthcharges makes for a very difficult path to steer.

You must also avoid the cavern walls, and there are some fairly tricky narrow tunnels to guide yourself through.

There are various stages within the game, in which you are attacked by various combinations of the above enemies. The only constant threat are the surface ships which appear in every stage.

The first stage has missiles and bases to destroy. The next has high speed fish intent on ramming your submarine - on this stage the missiles do not launch from the ocean floor. The next stage has bouncing underwater spiders which can move through the cavern walls - but they can only be shot in the open.

Later stages see differing combinations of these enemies, which stages where the missiles launch and there are fish and sipders to contend with. There are also stages where you move at a much faster speed making negotiation of the caverns even harder.

You start the game with 5 lives and an extra is awarded for 10,000 points.