Also, to the request for U-Boat references, there are MANY publications. Just pay a call to your local library, book store or Google search.
Squadron has several publications on the subject.
I agree, the recently re-published Anatomy of Ships "The Type VII U-Boat" is top stuff.
My favorite is "The U-Boat" by Eberhard Rossler. It is the definitive reference!!
You can look for "The German Navy at War - Volume 2 The U-Boat". Also a good reference is "Type VIIU-Boats" by Robert Stern. Another excellent reference is "Vom Original Vum Modell: Ubottype VII-C", but you should be able to read some German to fully understand how good this book is. Last, is another good reference, "U-Bootwaffe 1939-1945", but this time you understanding some Polish helps.
Off subject (because it is a Type XB) is "Germany's Last Mission to Japan, the failed voyage of U-234". This is a good view into one aspect of the U-Boat war not often discussed.