"War Beneath the Sea" by Peter Padfield. Good overview of submarine warfare, all nationalities, in WWII.

"Operation Drumbeat" by Michael Gannon. Excellent book-just finished it.

Clay Blair's series-"Hitler's U-boat War". Verrry detailed look at the Battle of the Atlantic. I'm currently reading Vol. 1.

"Dust on the Sea" by Edward L. Beach. Sequel to the already mentioned "Run Silent, Run Deep". There is a third one in the series called "Cold is the Sea" which takes place in the Cold War. All three are good.

:)