"We don't know how real well the submarine functioned," says Scafuri. "This is a case where they settled on what would work. That was hand power."
Confederate officials ordered the Hunley to Charleston, where it and other ships prepared to challenge a blockade of the harbor. The Federal Navy had deprived the Southern city of vital military supplies.
The Union fleet was well aware of the Hunley's danger -- to its own occupants.
Five members of the first crew died in August 1863 when it accidentally dived while its hatches apparently were open. The second crew's eight members succumbed in October when the Hunley failed to return to the surface.
The Confederate commander of Charleston, concerned about the loss of life and the expense of recovering the Hunley, ordered that any attack be made on the surface. Still, the vessel would be mostly under the water line during an attack.
Still, those who volunteered for the mission against the 205-foot USS Housatonic must have been well aware of the perils when approached by Hunley skipper Lt. George Dixon.
"This took some serious bravery here. I wouldn't want to go in there," says forensic genealogist Linda Abrams, who has conducted extensive research on the Hunley crew. "They know some other people had drowned in it. They had to have some faith in Dixon."
Dixon and his courageous crew, which included four European-born men, would target the Housatonic, the closest blockade ship.
Dixon routinely kept a worn good-luck charm in his pocket: A gold coin that was bent when he was wounded nearly two years before at the Battle of Shiloh in Tennessee.
In 2001, the shiny talisman was found in the laboratory, along with Dixon's presumed remains. Only one crew member has been positively identified through DNA tests.
Menacing object approaches wary ship
On a chilly February evening 150 years ago, the Hunley set out from Breach Inlet, which separates Sullivan's Island and what is now called the Isle of Palms. The vessel churned toward the Housatonic, about 4 miles away, at an estimated speed of 2 to 4 knots.
One of the crew members would have been in charge of bellows, providing sufficient air to breathe when the hatches were closed.
Friends of the Hunley, a nonprofit group established by South Carolina's Hunley Commission, provides a history of the mission on its website.
"While the cold bit through the lookout's coat ... men poured sweat over hand cranks that powered a spinning propeller while their captain manned the dive planes -- steering man, iron, anxiety and raw courage towards its final destination."
"A lookout aboard the Union Navy's largest ship was tired, cold -- but restless. Talk of a Confederate secret weapon was in and out of his thoughts. Suddenly he spotted something move in the chilly waters. A porpoise? There were certainly a lot of them around. But something about this one didn't seem right."
Alarms went out on the Housatonic, which carried 12 guns.
The Hunley was too close and low to be hit by artillery fire, so crew and officers of the Union ship fired small arms, rifles and even a shotgun at the approaching menace.
Once in place, a submarine crew member managed to pull the lanyard for the 135-pound torpedo, attached to a 16-foot spar that was still connected to the Hunley's bow.
The Housatonic sank within minutes.
Five members of the Union vessel died; 150 others were rescued.
All kinds of scenarios for loss of Hunley
A Union sailor who climbed to the Housatonic's rigging and a Confederate observer on the shore reported seeing a blue light emanating from the Hunley, signaling mission accomplished.
"That indicates someone was conscious after the sinking of the Housatonic," says Robert Neyland, head of underwater archaeology for the Naval History and Heritage Command and former director of the Hunley Project.
But researchers have been unable to precisely pinpoint the source of the light -- whether it came from a lantern or pyrotechnic device that sent out various signal colors. And it's possible the light came from Union rescuers.