A Confederate sub that sank with its eight-man crew 150 years ago is nearing the end of a painstaking cleaning process expected to shed light on why it never returned to shore, reports AP. About 70% of the HL Hunley's hull has now been revealed at a lab in North Charleston, SC, and the senior conservator on the project says the work is providing clues about why the Hunley sank in 1864—but he's not revealing them just yet. "It's too early to talk about," he says. "We have a submarine that is encrypted. It's like an Enigma machine."
Before it went down, the Hunley became the first sub in history to sink an enemy ship, the target being the Union's USS Housatonic. "Her victory proved the viability of submarines as a weapon," writes Devin Poore in the New York Times, and both the North and South applied the lesson as the war continued. The hand-cranked sub was discovered in 1995 off the coast of South Carolina and finally raised in 2000, but restoration work involving a chemical bath didn't begin until last May. (One theory is that the sub's crew was knocked unconscious by the shot that struck the Housatonic.)