[starman2003]

There have been quite a few books on submarine warfare in WWII. Besides Iron Coffins which has a number of errors or inaccuracies, and a plethora of books on US subs. Lone Wolf the Life and Death of U-boat ace Werner Henke wasn't bad. Blair's Hitler's U-boat war is a pretty good read. For info on a more obscure aspect of the war, there's The Japanese Submarine Force and World War II.