Ths line jumps out at me:
"He said that a Union sailor holding onto the rigging of the sinking Housatonic saw a blue light in front of another Union vessel coming to the aid of the Housatonic."
There will always be speculation about why the Hunley sank but with the missing window lights noted in the cupola, I wonder if the swell from the other Union ship might have swamped it, adding to the weight and negative bouyancy if it was leaking some. The bodies were found pretty much where they would have been when operating the sub so the extra water weight may have contributed to the effort needed to power it and depleted the usable air rapidly. I had never heard the sighting of the light in front of the incoming ship. Maybe that is what sent the Hunley to the bottom.