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“By the end of the war, the Germans had suffered 30,000 dead and 5,000 captured U-boatmen from a deployed U-boat force of 41,000 men (latest German assessment), the worst casualty rate sustained by any armed force over a protracted period in all of history, and the milk cows suffered their full share of this carnage.”
― John F. White, The Milk Cows: The U-Boat Tankers, 1941–1945