1941. America had just entered the war. But terrifying unseen weapons were stalking US targets, sinking over 400 ships just miles from American shores in the worst naval defeat in United States history. The stealthy predators were German U-boats, Hitler's deadly warships of the deep. It was cataclysmic--with bodies and wreckage washed ashore on the eastern seaboard. But the Allies ultimately triumphed, sinking over 700 enemy subs. Fifty years later, the drama behind this wartime state of siege resurfaced when a team of divers discovered an unidentified German U-boat off the New Jersey coast. What boat was it? And what secret mission brought it there? Discover the identity of this mysterious sub, and trace the history of undersea warfare and travel to Germany to see World War II history rewritten.