No assignment in the Third Reich’s war machine, nay not even the fearful eastern front, was as dangerous as service in the Kriegsmarine’s U-boat fleet. Terrors of English shipping in the early war years, these submersible predators became prey once overwhelming U.S. materiel poured into the theater, and Allied intelligence started cracking German signals. By war’s end, fully three-quarters of the wartime U-boat personnel had sunk into watery graves. And on top of all the intrinsic perils of fighting a losing war from the inside of a submerged tin of beans, you’d better do it with enthusiasm or you’ve got...