The player is trapped in a crashed Atari 2600 nuclear submarine which has begun taking on water. They need to escape by making their way up the levels of the submarine one at a time. Each floor has two hatch keys that need to be collected in order to unlock the elevator to the next level. There is a time limit, though; if you take too long the floor will flood and you'll be unable to escape.
As you progress through the game, you'll have to navigate around moving torpedoes on the submarine's floor while also avoiding being stunned by them. The goal is to collect the necessary hatch keys and reach the top of the submarine before time runs out.