On Friday, scientists announced one of the final steps that should help explain what happened after the hand-cranked sub and its eight-man crew rammed a spar with a powder charge into the Union blockade ship Housatonic off Charleston in February, 1864.
Early next year the 23-ton sub will be delicately rotated to an upright position, exposing sections of hull not examined in almost 150 years.
When the Hunley sank, it was buried in sand listing 45 degrees to starboard. It was kept that way as slings were put beneath it, and it was raised and brought to a conservation lab in North Charleston a decade ago.
Sunday marks the 10th anniversary of the raising of the Hunley, discovered five years earlier by shipwreck hunter Clive Cussler.
As thousands watched from boats and the shoreline, the Hunley was brought from the depths and back to the lab by barge. Thousands turned out again in April 2004 when the crew was buried in what has been called the last Confederate funeral.
During the past 15 years, about $22 million has been spent excavating and conserving the Hunley, according to Friends of Hunley, the nonprofit group that raises money for the project.
About $10.8 million came from the state and federal government, with the rest raised through donations and tour ticket and merchandise sales. About a half million people have seen the sub that sits in a tank of water at the conservation lab.
An economic analysis earlier this year estimated the project has returned its investment many times over.
The study found that publicity from hundreds of news stories, a half dozen documentaries and a made-for-TV movie has generated at least $30 million in a state where tourism is an $18 billion industry.
"I have absolutely no misgivings," said state Sen. Glenn McConnell, the chairman of the South Carolina Hunley Commission. "The state is spending millions of dollars to get its message out to get people to visit here and the Hunley, in just one new historic revelation, makes history and makes news all over the world."
U-Haul also has the picture of the Hunley on the side of 1,200 of its rental trucks that travel throughout the country, essentially free advertising that the company says would otherwise be worth $117 million.
Rotating the sub will allow scientists to, for the first time, completely examine the Hunley's hull.
It's a delicate operation, involving replacing the existing slings before the sub is turned upright. The pressure on the straps will be monitored electronically and a laser will monitor to make sure the surface doesn't get warped.
The Hunley is "a ghost of an iron object," said senior conservator Paul Mardikian, adding it has "hundreds of different parts and everything has to move together."
Putting it upright should provide clues to the sinking.
Was it damaged by fire from the Houstonic or perhaps struck by a second Union ship coming to the aid of the blockade vessel? Were the Hunley sailors knocked out by the concussion of the explosion that sank the Housatonic?
The clues indicate the crew died of anoxia, a lack of oxygen which can overtake a person very quickly, and didn't drown. The remains showed they were at their crank stations and there was no rush for an escape hatch.
McConnell concedes he didn't expect the project to take so long and thought it would have been in a museum by now.
"The Hunley is a very complex artifact and we decided we had only one chance to do it and that was to do it right," he said.
He estimates the Hunley could now be displayed in a museum by 2015.
Conservation of such artifacts often takes years, underwater archeologists say.
It was almost 30 years before the Swedish royal warship Vasa, which sank in 1628 in Stockholm Harbor and was raised in 1961, went on display in a permanent museum.
Scientific reports on the Vasa are just coming out, said Lawrence Babits, director of the Program in Maritime Studies at East Carolina University.
"The Hunley is iron and the iron isn't very thick and iron that has been in salt water is in a very nebulous state," he said. Putting it in shape where it can be displayed "does take time."
Frederick Hanselmann, a field archaeologist at the Institute of Nautical Archaeology at Texas A&M said the most painstaking part of conserving iron objects is removing the salts from years in sea water.
Conserving a ship cannon alone can take three to four years, he said.
"For conservation it's not an unusually long time, especially considering they are conserving an entire submarine," said Mark Gordon, the president and chief executive officer of Odyssey Marine Exploration.
The company salvaged more than 50,000 coins and other artifacts from the wreck of the SS Republic off Savannah, Ga., in 2003 and while many of those coins are being displayed, some of the artifacts are still being conserved seven years later, Gordon said.
Hunley archaeologist Maria Jacobsen isn't surprised the cause of the sinking hasn't been found and expects a new series of questions and answers when the Hunley is rotated.
"I do think with persistence and patience and a good deal of luck we will get there," she said.