You are the commander of a sub patrolling enemy waters. Your mission is to rid this area of deadly mines and make these waters safe for travel. Use [the joystick] to move your sub in the direction you choose. The fire button will launch a torpedo with a limited range. You have no limits on time or number of times you can fire.
Sub was written by Lee Pappas and published as type-in source code in A.N.A.L.O.G. 400/800 Magazine (ANALOG Computing) No. 1, January 1981.