A few minutes after the attack, the Hunley itself sank from view, not to surface again for 136 years. Five years ago, however, the remains of the sub were located 27 feet below the sea, about four miles from Charleston, by the writer Clive Cussler (though some dispute his priority). Last August, the hulk was finally lifted from the bottom in a $17 million operation that brought together federal and state agencies along with the Friends of the Hunley and the National Geographic Society.

According to the NGS, divers looped 32 slings around the wreck to support its 65,000 pounds, and cushioned it with inflated foam pillows. The slings were attached to a steel frame that held the sub as a crane lifted the assemblage to the surface, where it was placed on a barge to be towed back to shore.

The Hunley was designed and built by two New Orleans engineers in the steam gauge manufacturing business, James McClintock and Baxter Watson, with financing from a local lawyer and planter, H.L. Hunley. Their third craft, built in Mobile, Ala., and christened the H.L. Hunley, carried a crew of nine and was powered by eight of them cranking a direct-drive shaft extending lengthwise through the vessel.

Last moments: The H.L. Hunley slices through the moonlit waters of Charleston Harbor after torpedoing the Union warship Housatonic, as seen here in an artist's rendering.

According to Dan Dowdey of the South Carolina State Museum in Columbia, the builders adapted high-pressure steamboat boilers 1/2- to 5/8-inch thick for the hull. Dowdey said the reinforcing bands may have been moved to the inside, since the pressure to be resisted in this case was outside the vessel. The boilers, he said, were apparently split longitudinally so 10 inches of plate could be riveted in, to enlarge the sub's diameter. The result was an interior chamber 41 or 42 inches wide, 52 inches high, and 39 1/2 feet long.

According to Fritz Hamer, the museum's curator of history, one of the first surprises when the vessel was recovered was the smoothness of the hull. The rivets were found to be flush with the surface, indicating an unexpected level of sophistication in riveting.

The Hunley had a keel weighing three or four tons, split into three sections that could be jettisoned in case of emergency. Diving planes 6 feet long and 10 feet wide were mounted in line with the forward conning tower and operated by a lever inside the sub.

The craft had two hatches, front and rear, which also served as conning towers. There were no periscopes, although the towers had glass ports. They would have provided some illumination near the surface, as would a row of five skylights, but once the craft dived, there was only a single candle that was to serve as a warning when the oxygen was used up—perhaps giving the alarm a bit late. The only navigational instrument was a compass, which is of limited use in an iron chamber.

After the Hunley was shipped by rail to Charleston, misfortune seemed to dog the submarine. During preliminary testing, the craft was swamped, with the loss of most of her crew. With a new crew aboard, headed by Hunley himself, once again the sub sank, this time with the loss of all hands, including the epo-nymous Hunley. It took weeks to recover the craft, but it was finally prepared for its mission.

A 17-foot-long spar made of iron pipe, attached to the front end, close to the bottom of the vessel, was outfitted with a primitive 135-pound "torpedo"—actually something more like a land mine, according to Hamer. A 150-yard-long lanyard could be pulled to ignite the fuse.

Initially, things went according to plan. The torpedo deposited, the sub retreated and set off the bomb, which sent the Housatonic to the bottom in minutes with the loss of five lives. The sub's crew signaled that they were returning to shore, but they didn't arrive.

For now, the Hunley lies in a tub of water at the Warren Lasch Conservation Center, in the former Charleston Naval Shipyard. Preliminary conservation must be done quickly, before deterioration sets in. Researchers expect to take years to examine the vessel and its contents, which presumably include the remains of the crewmen.

"We have a lot to learn about this thing," Hamer said. "It's important for what it contributed to the future of submarine technology. The Hunley was the first sub that got results. It proved that it could be done."

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