Dangerous Waters on steam sale now for 3,74€

[Nil]

It's really a superb naval sim (even if it's from 2004 or 5)
The modding community is still going strong on http://www.subsim.com making it still the best damn naval sim of all times!
Still multiplayer going on with tunngle.

Nothing beats cruising along in a nuclear sub!

You learn a lot from watching the tutorials by FPSchazly https://www.youtube.com/user/FPSchazly/playlists?sort=dd&view=50&shelf_id=22 actually enough not to more then just take a glance at the 700 page manual.