Someone will come along and point you to books and resources soon enough.
I personally cant help you really in that department. But I can recommend a few movies you might enjoy.
Das Boot of course, Run Silent Run Deep, The compas rose aka The Cruel Sea.
Of course they will also be quick to point out that 20,000 tons on a single patrol is a bit ... unrealistic.
If you are interested in a more 'realistic' play experience you may want to look into the wonderful mod's available. I wont recommend any off hand as there are quite a few to choose from.
Well thats more than you asked for. Enjoy and good luck.
