Mailing the story:

Danger from the deep is nice open source submarine sumilator game. According to their website "Danger from the Deep (known as dangerdeep or DftD) is a free (as in free speech), Open Source World War II german submarine simulator. The program and source code is available under the GPL license and most of the artwork/data is released under a Creative Commons license (Attribution/NonCommercial/Non-Derivative works)