At least one of the blue light accounts was someone physically present and witnessed the exchange between Dixon and Danzler about the signal plan. Based on the postions of the respective Federal ships that day, if the attack worked, basicly the Hunley should have been the only thing left afloat (hopefully still) in that general direction as viewed from Battery Marshall. Since the eyewitness account, and most everyone else in Charleston apparently was aware of the reported blue light. It has been generally accepted that this was the type of signal used. Also the issue that anything else available at the time that could project a light across the distance needed would be able to fit through the hatch into the vessel. Blue Light was about the only feasible choice they had to use. Unfortunately no one gave reference if the "two" reported blue lights were to be used at the same time or one after the other, nor who from which hatch would actually be doing it.
Other items of interest... According to other written accounts about diving-surfacing it seems they practice this quite a bit. So seemed to be of second nature. The dive fins seemed to work quite well and very quick. This was the given cause of the first sinking. The commander was nearing his destination and opened the front hatch. While climbing up he accidently stepped on the dive fin control lever. The vessel immediately nosed down and flooded through the open hatch. Several managed to get out, five didnt.
The commander had one wheel control that steered the rudder. Beside him was a lever that controled the dive fins. In front was a stop cock valve that opened for water intake into the fore water ballast tank. Another lever that pumped the water out of it. Hunley himself mentioned that 2-3 cranks on the pump lever was sufficient to bring the vessel to the surface.
What most would view as a critical design flaw is that the internal fore-aft water ballast tanks didnt have tops. If not properly monitored and worked (or it failed)it would fill and spill over into the vessel flooding same. This was the determined cause of the second sinking. Hunley decided to take the vessel under, opened the front stop-cock to fill the ballast. It apparently wasnt going under quick enough or for whatever reasons he also used the dive fins. Immediately it plunged under and into total darkness. He then was apparently fumbling to get a candle lit. Not realizing the stop-cock was still wide open. It quickly begain to flood the vessel and it nose dived embedding itself into the sand bottom and filled with water. Hunley was found with an unlit candle in one hand and the other over his head against the hatch lid, at one of the only remaining small pockets of air. The securing latches on both hatches were in the open position, but the pressure of the water prevented them being opened. Most of the crew drowned the others slowly died of asphyxiation.
The obvious panic that occured inside the vessel was quite disturbing. They were found at or under the hatches, and the crew was quite derranged inside. Everybody already knew what a sinking panic looked like. The later crew knew that such an event would be a horrible death. They had an agreed upon pact of sorts that if they were trapped and totally unable to surface, that they would open the ballast tanks and quickly flood it themselves. It thought to be a quicker death than by hypoxia. When the Hunley was recovered the stop-cock valves were found in the closed position. This was one of the reasons the focus on the stop-cocks was of intense interest to see if thats what they did, apparently it wasnt.