The H.L Hunley was the first submarine built during the American Civil War, and after the vessel became the first submersible to sink another ship in wartime, it sunk off the coast of South Carolina. Now, researchers are able to study the construction and design of this historic marine vessel, built by a desperate Confederate military as their forces suffered a series of defeats on the ground.

The Hunley was recovered from the seafloor in 2000, but the pioneering submersible was encrusted with a thick layer of rust, hardened sand and silt. Around 70 percent of that material has now been removed, following six months of work, revealing the hull of the submarine for the first time since it was launched on its fateful mission.

The nearly 40-foot long vessel was built in Mobile, Alabama, and first launched for testing in July 1863. During one exercise, the Hunley sank for the first time on August 29, 1863, taking the lives of five crewmen on board. The vehicle was recovered by the Confederacy, and restored. The submarine sank for a second time on October 15, 1863, killing all eight people inside the ship, including the inventor, Horace Hunley. Once again saved from the seafloor, the Hunley set out on its first - and last - military mission.

On February 17, 1864, crew aboard the submarine successfully attacked the USS Housatonic, killing three seamen and two officers on the Union ship. The Hunley later sank on the way back to port, for reasons still unknown to historians, taking the lives of all eight people in the vehicle. From training to its lone attack, the Hunley took the lives of 21 southerners, while killing just five union troops. Despite this, the ship brought the reality of submarine warfare to the forefront of modern military thinking.

The Housatonic was participating in a naval blockade of southern states, and was stationed in waters off of Charleston, South Carolina when she was sunk. The design of the Hunley, a revolutionary ship, was a secret of the Confederacy, so little information is available. Researchers are hoping that examination of the recovered ship could help reveal how and why the submarine sank after its lone voyage. Some information may have already been found by investigators.

"I would have to lie to you if I said we had not, but its too early to talk about it yet. We have a submarine that is encrypted. It's like an Enigma machine," Paul Mardikian, senior conservator on the Hunley project, said.
 
The Hunley was found in 1995, and remains of the crew inside were honored by mourners in Confederate and Union uniforms in 2004.

A video showing the restoration of the Hunley is available on the Friends of the Hunley YouTube channel.