You are now a member of Silent Service , the US Navy Submarine command. For a long while after Pearl Harbor, you are the only forces capable of striking back at the Japanese in the Pacific. Take one of the "fleet boats" and go on extended patrols from Hawaii, Australia, or New Zealand. Set your difficulty/realism level and time period - early means less tech for juicier targets, later means tougher escorts, more tech, lousier targets.
You can choose among practice run against some old hulks, recreate historical convoy attacks, go on a single patrol, or go on your own campaign, which lets you go multiple patrols until you die, get promoted, or survive the war. The freedom to play as you like is part of the Silent Service experience.
The challenge of Silent Service lies in its realistic portrayal of submarine warfare. Factors such as dud torpedoes, maximum depth, and more will test your skills. How well will you do when matched against history?