A good sim for its time. Too short, though.
Basically, you command a submarine in varying missions using a point and click interface on different screens, including weapons, nav, etc. The controls were fairly straight forward and it was simple enough to maneuver around and even engage the enemy and fulfill the missions. There was one mission, though, that I was never able to beat, and was the mission where you were supposed to shoot some cruise missiles at some land target. I could never beat that one, what a shame.
The other missions will have you facing off against surface ships and other subs. If you like sims, you may give this one a shot.