Long before 9/11, a far deadlier, little-known attack from the ocean depths struck our shores, lasting three-and-a-half years and claiming 5,000 lives. Now, famed undersea explorer Bob Ballard, discoverer of the Titanic, investigates the wreck of one of the attack craft, a German submarine that lies at the bottom of the gulf just a few miles off New Orleans. U-166 was part of O...