Researchers are now getting the chance to discover what caused a Confederate submarine's demise over 150 years after it sank to the bottom off South Carolina's coast, the Associated Press reported.  

Scientists had access to the hand-cranked submarine H.L. Hunley since it was recovered in 2000. But it needed to undergo a grueling conservation process to expose the hull for examination.

This week scientists announced that enough of the hull has finally been exposed, allowing them to look inside and discover why the Confederate submarine never returned to the surface with its eight crew members following a Civil War battle in 1864.

"It's like unwrapping a Christmas gift after 15 years," Paul Mardikian, senior conservator on the project, told the AP. "We have been wanting to do this for many years now."

In February 1864, the Hunley went up against the USS Housatonic, a ship the Union used in its blockade on the South. The Hunley successfully sank the blockade ship but the sub and crew never returned to the surface.

One theory was the crew ran out of oxygen before they cranked the sub to the coast. Another is that the force of the blast needed to sink the ship knocked the crew unconscious.

Scientists at a conservation lab in North Charleston covered the submarine in a crude paste made of sediment, rust and encrusted sand. It was then immersed in a sodium hydroxide solution that made the paste loose enough for scientists to chisel away at, the AP reported. 

Mardikian said the now exposed hull has revealed details about what caused the sinking, but he did not elaborate.

"I would have to lie to you if I said we had not, but it's too early to talk about it yet," he told the AP. "We have a submarine that is encrypted. It's like an Enigma machine."

As for the crew, their remains were removed from the sub and given a proper burial in South Carolina in 2004.