You are captain of a submarine and the computer is captain of a gunboat. The speed of the gunboat is given at the beginning of the game. You fire torpedoes at the gunboat. To sink it, you must hit it twice in at least two vulnerable places, or once in a vulnerable place and twice in any other part of the hull. But, if you ever miss, the gunboat will open fire on you. If this happens, you alternatively fire at each other until you sink the gunboat or he sinks you.