When the resting place of the American Civil War submarine H L Hunley was finally discovered in 2000, marine archaeologists found the eight-man crew still at their posts, frozen in time.
It was as if the men aboard had been killed instantaneously – none were found to be trying to fix damage or abandon the sub.
As the shipwreck was recovered, experts pored over the craft to try and determine what had caused it.
The Hunley was a Confederate vessel that sank after a battle with the 23-gun blockade ship USS Housatonic in 1864. It’s the first submarine in the history of naval warfare to sink another ship.
But in doing so, the Hunley also sealed its own fate.
Now, scientists from Duke University believe the weapon system used by the Hunley to take down the Union vessel was what caused the mysterious death of the crew on board.
Rather than use standard self-propelled torpedoes, the Hunley mounted a 60kg keg loaded with gunpowder on a 5-metre pole on the front of the bow. This so-called spar was then rammed into the timber of the Housatonic’s hull and left to explode, crippling the battleship.
Unfortunately, the researchers now believe the shockwave from the explosion is what killed the sub’s crew before they even knew what was happening.
The shockwave, believed to be travelling at 1,500 metres-per-second through the water passed through the iron wall of the submarine and instantly ruptured the blood vessels, lungs and brains of the men inside.
“This is the characteristic trauma of blast victims, they call it ‘blast lung,'” explained Dr Rachel Lance from Duke University.
“You have an instant fatality that leaves no marks on the skeletal remains.
“Unfortunately, the soft tissues that would show us what happened have decomposed in the past hundred years.
“Shear forces would tear apart the delicate structures where the blood supply meets the air supply, filling the lungs with blood and killing the crew instantly.”
The research team figured out this was the case after painstakingly recreating a scale model of the Hunley and it’s explosive load – then detonating it and watching what happened.
The actual vessel is currently in Charleston, South Carolina, where a team of experts from Clemson University are studying and restoring the craft.
The team hopes to eventually restore it as close as they can to its original appearance.
This has involved soaking it in a mixture of sodium hydroxide and a small electrical current to loosen the covering.
The team keep the boat submerged in a 75,000-gallon tank of water and chemicals around three times a week drain it before chipping away at the sediment covering it.
But the operation to clean out the inside is nowhere near finished, with it taking years to fully excavate a small cabin.
Conservator and collections manager, Johanna Rivera-Diaz, said: “It’s tough physically to do this every day.
“You are wearing special suits and using chemicals with high pH levels.”
The eight men that died were remembered at a large ceremony.
They were believed to be the submarine commander, Lt. George Dixon of Alabama, James A. Wicks, from North Carolina, Frank Collins of Virginia, Joseph Ridgaway of Maryland and four foreign-born men who very little is known about.