amzing game but dont buy unless your desprate as sea power (another game made by the same devs) is coming out in november which will have submarines and suface ships and air craft carries and planes

First things first: This isn't a hard-core subsim like Dangerous Waters. You don't have to choose different bandwith types of sonar, perform target motion analysis or even manually operate towed arrays. It's a game - but a fun one. I've very much enjoyed the exciting cat-and-mouse games with enemy fleets or subs.
Important note: Many players become frustrated with this game because they don't understand the stealth/detection mechanics. Admittedly, those aren't explained at all in the game tutorial. It's all about the numbers on the "signature" screen, they'll tell you all you need to know about who's able to hear whom. Explanations and tutorials are available online.

The most Fun Sub game around for the cold war.
Also highly recomend the DOT mod as well for this game.