From 1939 until 1942, Hitler's U-boats-the submarine fleet dubbed the "gray wolves"-threatened to accomplish what his air force had been unable to achieve: to starve Britain into submission. The ensuing struggle for control of the storm-tossed Atlantic trade routes became a full-scale war-within-a-war, and one which led to astounding losses: Allied powers would lose more than fifty thousand men, and fifteen million tons of shipping, over the course of the conflict.Through exclusive interviews with survivors on both sides-including those given for the first time by former U-boat crew...