A century and a half after a legendary Confederate submarine mysteriously sank, conservationists in Charleston, SC, are still working to figure out why. Their latest step could be key: Experts yesterday placed the 40-foot HL Hunley in a solution that's 1% sodium hydroxide and 99% water, the Post and Courier reports. The caustic mixture should, over the course of several months, soften the hardened sand-and-shell layer that coats the iron vessel's hull. Each day, the tank the Hunley is submerged in will be drained, allowing scientists to work to scrape that layer off before refilling the tub once again, reports the AP. Because under that layer "is the possibility of new information about the attack," says an archaeologist.
The sub was the first ever to sink an enemy ship—in this case, the Union's Housatonic, which was part of a blockade around the key Southern port of Charleston. Why the sub itself sank right afterward remains a mystery. "Chiseling away the concretion (of sand and shell) will allow us to travel back in time, potentially helping us learn what happened to the Hunley and her crew that night," says South Carolina Lt. Gov. Glenn McConnell. The sub currently sits in a 76,000-gallon tank, and once the salt is fully removed from the hull the Hunley will be able to be safely displayed without being submerged in water. The full conservation process is expected to take five years. (Click for one theory on what sunk the Hunley.)