Donitz's Crews: Germany's U-Boat Sailors in World War II by Col. French L. MacLean, US Army (Ret.)
With dozens of historical documents and over 400 photographs, the author not only presents a comprehensive history of U-boat crews and the undersea war, but also shows how those with an interest in the U-boat war can find U-boat-related artifacts and how they can trace many to specific boats - and then research what those boats and crews accomplished.