On February 17, 1864, the H.L. Hunley, a 40-foot-long Confederate submarine, sank to the bottom of the ocean off Charleston, South Carolina. The reason why is still a mystery.
That day, the Hunley became the first submarine to sink an enemy ship during battle when it embedded a torpedo in the USS Housatonic’s hull. After the torpedo detonated and sank the ship, the sub signaled to shore that its mission had been completed and started heading back to land…but it and the eight crew members aboard never returned. The sub sank to the sea floor.