Sub Commander (Geoff Ayre)
"Sub Commander is a free, independently developed roguelike submarine simulator with an emphasis on realism and freedom of choice.
Originally, the game was envisioned to be a kind of cross between Dwarf Fortress and the film K-19 The Widowmaker but it is rapidly growing to a full featured submarine warfare simulator.
Eventually I plan to simulate all aspects of cold war era naval and aerial combat, so the player's submarine will be in the midst of a dynamic, procedurally generated global war." - Author's description
Download the latest version here (Windows)