The mystery of how the crew of one of the world’s first submarines died has finally been solved - they accidentally killed themselves.

The HL Hunley sank on February 17 1864 after torpedoing the USS Housatonic outside Charleston Harbour, South Carolina, during American Civil War.

She was one of the first submarines ever to be used in conflict, and the first to sink a battleship.

It was assumed the blast had ruptured the sub, drowning its occupants, but when the Hunley was raised in 2000, salvage experts were amazed to find the eight-man crew poised as if they had been caught completely unawares by the tragedy. All were still sitting in their posts and there was no evidence that they had attempted to flee the foundering vessel.