In May 1943, Allied sea and air forces won a stunning, dramatic, and vital victory over the largest and most powerful submarine force ever sent to sea, sinking forty-one German U-boats and damaging thirty-seven others. It was the forty-fifth month of World War II, and by the end of May the Germans were forced to acknowledge defeat and recall almost all of their remaining U-boats from the major traffic lanes of the North Atlantic.

At U-Boat Headquarters in Berlin, despondent naval officers spoke of "Black May." It was a defeat from which the German U-boat fleet never recovered. Given the strategic importance of the events of May 1943, it is natural to ask, How did Black May happen and why? Who or what was responsible? Were new Allied tactics adopted or new weapons employed? This book answers those questions and many others.