The Hunley and the 'blue light'
On 17 February 1864 the Confederate submarine H. L. Hunley sank USS Housatonic off Charleston, the first submarine to sink a warship, then vanished with her eight crew.
1864 CE · 32.72, -79.77 · status: explained
The account
A lookout on Housatonic reported a 'blue light' on the water after his ship sank, and Battery Marshall reported receiving the submarine's signals, which later writers said were two blue lights. A legend grew of a blue lantern shining from the lost boat. The wreck was found in 1995 and raised in 2000; the lantern aboard had a clear lens, and 'blue light' then meant a navy pyrotechnic flare. The crew were found at their stations with no injuries, and the cause of the sinking is still debated, including blast injury from the torpedo.
The sceptical view
The blue light was a standard signal flare; there is no phantom lantern.