http://www.mobygames.com/game/das-bo...oat-simulation
This is a description of this game, an old DOS game, inspired by the movie: 'Das Boot' and even named after it.
(Didn't see anything illegal about the link above
)
I liked Wolfpack better though, was just cooler and gave you the option to play any sub in the wolfpack, or just any other vessel in that mission, including freighters, tankers and destroyers.