Aces of the Deep

From Wikipedia

"Aces of the Deep" was the last installment of Dynamix "Aces" series, which included the flight simulators Red Baron, Aces of the Pacific and Aces Over Europe. However, unlike its predecessors, "Aces of the Deep" places you at the command of a German Navy U-Boat during the Second World War. The game includes single mission mode, where the player can choose to attack a convoy, a task-force of warships (consisting of cruisers and/or battleships), or a carrier task-force in a variety of conditions. There are also several historical missions where the player can replay the role of some of Germany's greatest U-Boat captains.