In Sega Genesis 688 Attack Sub, you control a submarine as it attacks a series of targets in a watery setting. The sub is able to fire torpedoes and missiles at targets, and you can also use the submarine's torpedoes to sink targets. The game features three different modes: singleplayer, co-operative multiplayer, and versus. In co-operative multiplayer mode, you and up to three other players must work together to defeat the obstacles in order to reach the target. In versus mode, you can challenge other players to a game of strategy and tactics.