For more than 150 years, people have been trying to figure out why the H.L. Hunley sank.
When it torpedoed the Union ship Housatonic off the coast of Charleston in the cold winter of 1864, it became the first submarine to sink an enemy ship in battle — a feat that would not be repeated for another 50 years.
And then it vanished.
So what happened? Over the years, people have speculated that Housatonic sailors fired a lucky shot that cracked the sub’s brittle cast-iron hull, causing it to fill with water and sink.
Others believe the crew, forced to retreat to the ocean floor, ran out of air waiting for the tide to turn.
One eyewitness account fuels a theory that another Union blockade ship ran over the sub.
Last week, Duke University claimed its researchers had solved the lingering mystery. Biomedical engineers there conducted tests and concluded the Hunley’s own torpedo blast incapacitated the eight men inside.
“The crew died instantly from the force of the explosion travelling through the soft tissues of their bodies, especially their lungs and brains,” Duke announced.
The idea that the sub was too close to the blast has been around for years, a theory that gained credibility when scientists discovered its torpedo detonated on contact.
But the U.S. Navy said the blast didn’t kill the crew.
In a forthcoming paper that will be published by the Society of Naval Architects and Marine Engineers, two Navy scientists — who conducted their own tests — say the black powder used in the Hunley’s torpedo, when ignited, would produce a low-magnitude pressure pulse, not a shock wave.
Basically, Navy scientists say the explosion might have knocked the men in the sub around a bit, but didn't cause any serious injury. Which is what Paul Taylor, a spokesman for the Naval History and Heritage Command, has said.
"The Navy has already examined the concussive wave theory. We found it highly unlikely to have injured the crew, let alone caused their deaths."
That was also the conclusion of forensic pathologists who examined the crew’s remains. James Downs, former chief medical examiner for the state of Alabama, said there was no sign of trauma on the crew's brains — all of which were intact.
“The Duke study is interesting, they just unfortunately didn’t have all the facts,” Downs said. “This is something we discounted quite a while back based on the evidence.”
Rachel Lance, who earned a doctorate in biomedical engineering from Duke with her research, said the Navy tested for a concussive wave that caused blunt force trauma to the crew while hers focused on pressure waves in the air.
“The blast injuries we studied occurred when the blast (concussive) wave itself transmitted into the hull of the submarine and caused lethal trauma to the lungs,” Lance said. “All that the two theories share in common is that there was an explosion.”
Kellen Correia, president/executive director of Friends of the Hunley, said without the data collected by Clemson scientists, and also by the Navy, Downs and Smithsonian researchers, it would be impossible to draw any definitive conclusions.
So, what happened? This is what we know:
On the evening of Feb. 17, 1864, the Hunley — a third-generation submarine built in Mobile, Ala. — left Sullivan's Island on the outgoing tide. It reached the Housatonic, nearly four miles offshore, around 8:30 p.m.
Housatonic crewmen spotted the approaching Hunley, but not soon enough to fire their cannons. The Hunley rammed its spar-carried torpedo into the Housatonic, and the blast sank the ship in five minutes.
Two men claimed they saw the Hunley about an hour later, and those were the last confirmed sightings until 1995 when a dive team led by local archaeologist Ralph Wilbanks — working for novelist Clive Cussler — found the Hunley about a quarter-mile seaward of the Housatonic wreck.
The Hunley was recovered in 2000 and, since then, scientists at the Warren Lasch Conservation Center have been studying and conserving it. After 17 years, however, they say there's still no smoking gun.
But there are several popular theories.
When Cussler’s team found the Hunley, they discovered a grapefruit-sized hole in its forward conning tower. Some speculated that small arms fire from the Housatonic shattered the cast iron, allowing the sub to fill with water.
All scientists know for sure is that the hole in the sub came early in its history. But it could have been caused by an anchor snag. After the Civil War, cleanup crews dragged the ocean floor to clear the harbor channel of debris.
Loss of air
Many people believe the crew simply ran out of air. After the attack, the Hunley still had hours to wait for an in-going tide to get back to shore. To keep from drifting out to sea, and avoid Union rescue ships, they would have set down on the ocean floor.
Some have speculated the crew simply ran out of air and succumbed to anoxia, a lack of oxygen to the brain.
A collision at sea
The Housatonic watchman who claimed to have spotted the sub after the attack said the Hunley was floating directly in the path of the USS Canandaigua, a blockade ship coming to rescue Housatonic survivors.
Cussler favors this theory, not only because of the eyewitness account but also the strong physical evidence. Half of the Hunley’s propeller shroud is missing, but the half that remains bears three nearly uniform triangular cuts — like propeller strikes.
It would be nearly impossible for such damage to have occurred after the Hunley sank. It came to rest with that side of the shroud facing the ocean floor.
A curious broken pipe
The Hunley used ballast tanks to submerge, and the crew let water into those tanks through a valve on the hull.
Years ago, Hunley conservator Paul Mardikian discovered the brass pipe that carried water to the forward ballast tank had broken off the hull — a breach that could have caused the sub to sink within minutes.
Brass does not corrode, Mardikian said, so the damage was probably contemporary. He has suggested the sub's captain might have been thrown against the pipe, which stuck out at a 90-degree angle, upon impact with the Housatonic.
In its forthcoming report, the Navy lists this as a possible cause for the sinking. But there are discrepancies. Such a hole would have sunk the sub in three minutes, Navy research found. So how was it spotted an hour later?
And that’s the problem with the Hunley. For all the evidence that supports one theory, there are often clues that contradict it.
That’s why, 17 years after the Hunley was recovered, the scientists working most closely on the sub have refused to declare the mystery solved.
Reach Brian Hicks at firstname.lastname@example.org.