Please, dig deeper, the US Navy Submarine war against the Japanese is a complex and multi-dimensional story. There are many great books on the subject. SH4 has come a long way since its release and also deserves long study.
The Fleet Boat brought about technology to the war that is simply amazing for the time, if not for the torpedo problems its deadliness would have been ten-fold in tonnage.
So do a lot of reading, try out the mods there are many (more reading) and go on lots of patrols and see what you think of the Pacific. I did run SHIII for quite a time but now the Pacific has really put the hook into me...
Enjoy and Happy Hunting!