For more than a century, the H.L. Hunley rested at the bottom of the ocean just outside Charleston harbor, its crew entombed, its hull gradually encased in hardening encrustations.
When it was raised 15 years ago off South Carolina, it looked more like a barnacled sea monster than the world’s first combat submarine to sink an enemy warship. The Hunley sank in battle during the winter of 1864.
The remains of its eight sailors were removed in 2001, but research has continued and Thursday a conservation team announced that experts have now removed more than half a ton of the encrustations.
The result: The Hunley has much of the look and menace of a modern sub, and is clearly the ancestor of the U-boat and the nuclear submarine of today.
The work also revealed damage to the bow, from an explosion or a collision, but a conservator said that, by itself, did not solve the mystery of why the Hunley sank.
“I don’t think it’s a single event . . . that led to the sinking,” said Johanna Rivera, the Clemson University conservator and collections manager overseeing the project. “I think it’s a combination of factors and things that happened.
“Maybe they took in water, maybe they were unconscious, plus the torpedo explosion,” she said Thursday. “We haven’t found the smoking gun.”
On the night of Feb. 17, 1864, the crude Confederate vessel — which was made from a boiler, had no extra air supply and was powered by a hand crank — rammed a torpedo into a Union warship anchored off Charleston.
The Yankee ship, the USS Housatonic, went down, but so did the 14-ton Hunley with its captain and crew.
The Hunley had sunk twice before, killing part of one crew and all of another, when it set out on what was to be its final mission in the midst of the Civil War.
Even its namesake, Louisiana planter Horace L. Hunley, who had helped fund its construction, had perished at the helm in the second sinking.
After each disaster, the sub was located and raised. The bodies were removed through the vessel’s two narrow hatches, and the befouled interior was scoured clean.
Despite the sub’s grim track record, the Confederacy, with its weak Navy, remained eager for some way to break the Union coastal blockade that was strangling the rebellion in the closing months of the war.
The Hunley was much like a modern submarine, with a sleek, cigar-shape hull, diving fins to help it submerge and surface, and two stubby conning towers.
But underwater, the crew had only the air in the sealed hull to breathe. Light was provided by candles. And the sub’s barbed torpedo, at the end of a pole attached to the prow, had to be jabbed like a harpoon into the hull of a ship.
The sub would then release the torpedo, back up and detonate the explosive with a rope.
On its last mission, the Hunley torpedoed the 12-gun Housatonic, which quickly sank, killing a handful of the Yankee crew.
The Hunley failed to return, and later research showed that the torpedo exploded while still attached to the sub.
Searches after the attack failed to locate the Hunley, and it remained lost until 1995, when a team financed by adventure novelist Clive Cussler found it using sophisticated electronic gear.
After the Hunley was raised in 2000, a special conservation lab was built in North Charleston. There, the process of preserving and studying the boat, with help from, among others, the Navy and the Smithsonian Institution, has been underway.
Within the last year, Clemson’s conservators have painstakingly chiseled away 1,200 pounds of rock-hard concretion, being careful not to damage the cast and wrought iron underneath.
The removal of the encrustation allows experts to get at the hull and start removing the salts that help corrode the metal, Rivera said in a telephone interview. She said cleaning began in August 2014 and ended about two weeks ago.
They are now starting to clean encrustations from the interior.
Rivera said she found it extraordinary that the crew would serve on the Hunley, knowing that others had previously drowned inside.
“Getting into a narrow machine underwater,” she said. “It’s so small inside and cramped and you get claustrophobic . . . whenever they closed those hatches, that’s what is amazing to me.”