Around midnight on April 28, 1944, a force of 25,000 U.S. troops was preparing to make an amphibious landing at Slapton Sands, on the southern coast of England. The operation, known as Exercise Tiger, was a practice drill for the invasion of Normandy, just five weeks away. But things went badly. The night before, a British destroyer detailed to escort the convoy collided with another ship and was anchored at port, leaving the landing craft inadequately protected.
At about 1:30 a.m., German torpedo boats slipped into Lyme Bay and launched their weapons against the convoy. The toll: 749 Americans dead, four...