The object of the game is to maneuver an on-screen submarine, the "N-Sub," with the joystick and sink the enemy fleet with torpedo fire in the Cobalt Blue Sea. The player can fire torpedoes vertically and horizontally from their submarines by pressing two separate "FIRE" buttons. The player can hold the button longer to fire three torpedoes in rapid succession. Enemy ships attack the N-Sub with missiles, torpedoes and depth charges. A round of gameplay ends when the player defeats a wave of twelve enemy ships. Successive rounds increase in difficulty. The player has multiple lives, or chances to continue after being hit by an enemy ship, and can receive more lives by reaching high scores. The game ends when the player exhausts their lives.