Back when I was but a lad, I was a bit a of a WWII buff, and read through most of the WWII books available in my library. I always found the ones about submarines to be especially interesting, because of the stealth and bravery required. The US submarine force was pivotal to winning in the Pacific (and the German U-Boat force made things very hard in the Atlantic), accounting for the majority of the Japanese ships sunk during the war.
Today on Boing Boing, I came across a link to the "The Fleet Type Submarine Online", which is a set of Navy instruction manuals from just after WWII. If you want to know what it was like to be a sonar operator, or how the engines work, this is a great reference.