In this cassette-based game by Commodore you are the Commander of a battleship which can be moved left or right across the top of the screen (the ocean surface). Enemy submarines move at different levels beneath the ocean, releasing deadly mines (?) which float to the surface to destroy your ship. These must be avoided by rapid evolutions or by dropping depth charges to destroy them.
Up to five depth charges can descend at any time, and you score points by destroying mines or submarines. The main object however is to survive for a period of 90 seconds: points are scored for every second you survive.
This game is not easy: after an hour of playing on the lowest level, instances of surviving the full period of time were very rare. But it didn't hold our interest for long: graphics are mediocre for the C64 and the poor use of colour made if difficult to distinguish between depth charges and mines. (We suspect that, as for the Vic, Commodore's quality games are on cartridge - where at under £10 each they represent very good value for money.)