What secret signal did the crew use that night for the Hunley submarine?

Answer 1

On February 17, 1864, the crew of the Confederate submarine H.L. Hunley, after its successful attack on the USS Housatonic, which was blockading Charelston Harbor, used a blue carbide lantern to signal Confederate forces that the attack had succeeded and they were returning to base. They of course never made it back, but evidence found since the Hunley was raised intact has found that the cause of crew death was likely asphyxiation from lack of oxygen and not flooding damage from the attack as had been suspected. Had they made it back, it could've altered the course of the war.

The signal was seen by both Confederate forces at Fort Moultrie on Sullivan's Island and by the crew of the sinking Housatonic about 15 minutes after the attack, around 9pm. Since the type of lantern used has a limited visibility range (about a mile and a half) it is believed they were fairly close to shore when signaling. The reports of the lantern sighting and time are confirmed in official Union and Confederate records of the time.

Since the Hunley was raised, it has been rewriting the history books. Besides the recent finding that the crew likely died from lack of oxygen and not flooding, evidence that the explosive charge, originally thought to be detonated by a line attached to a fuse and activated by the Hunley backing away, may have in fact been electrically detonated. Copper wiring and battery remains have been found to indicate this.

It should be noted that the Hunley was never a Confederate States' commissioned Navy warship - she was seized from her private builders by the Confederates and given to the Confederate Army, and operated as a Confederate Army vessel.