Looking like a submerged locomotive, the Confederate submarine H.L. Hunley poked stealthily toward the Union ships blockading Charleston harbor on the night of Feb. 17, 1864, and rammed a harpoon-like torpedo into the U.S.S. Housatonic. Then, as the Hunley backed away under the power of its hand-cranked propeller, it triggered the torpedo's charge, sinking the Yankee warship in about three minutes. It was the first enemy ship ever lost to a submarine. But Rebel jubilation was fleeting. Minutes later the Hunley unexpectedly sank, creating a mystery that has endured to this day.
Now it may finally be solved. Discovered in only...