More than 150 years after the underwater vessel sank during battle, researchers are finally unraveling its secrets.

During a Union naval blockade, the crew of the submarine H. L. Hunley fire a torpedo into an enemy ship. But even though the attack is successful, their celebration is short-lived. Yes, something is wrong, and in the waters off the coast of South Carolina, eight Confederate men’s days look numbered.

For on that night in February 1864, lookouts awaited the Hunley’s triumphant return. But slowly, they realized that it would never come, even if the vessel appeared to keep sending out a signal. And for the next 130 years, the resting place of this historic submarine remained a mystery. Then, in 1995, the wreck was finally located, and experts began the task of unravelling a tragic story.

Frustratingly, though, it was a further five years before the wreck of the Hunley was raised to the surface. And at the Warren Lasch Conservation Center in North Charleston, SC, a team got to work restoring the vessel. But would they finally be able to solve the puzzle of what had happened to the submarine’s crew?

Image: Friends of Hunley via Twitter/Nature News & Comment

Over the years, a number of clues have emerged about what brought the Hunley’s men to a watery grave. But nobody has ever been able to determine exactly what sent the vessel down to the ocean floor. Now, however, researchers have made a startling discovery that may finally explain one of the Civil War’s most enduring mysteries.

So the story begins back in 1861, when the Civil War first broke out in the U.S.. Frustrated with President Abraham Lincoln’s progressive attitude, and his anti-slavery stance, a number of states attempted to secede. And for the next four years, forces from both sides engaged in a series of bloody battles across the country.

With the dawn of war, both the Confederate States and their Union counterparts in the north began developing combat submarines. And in the Louisiana city of New Orleans, the southern army sponsored the work of an engineer named Horace Lawson Hunley. Eventually, in February 1862, his first vessel – named Pioneer – was ready to launch.

Despite a successful trial, however, the Pioneer was abandoned when Union forces began to encroach on the city. Undaunted, Hunley and his team relocated to Mobile, Alabama, where they built a second submarine. And in January 1863, American Diver was launched. Apparently, it was painfully slow, but that didn’t stop the Confederate Army using it to attack Union forces.

Now the Union was engaged in a blockade against the southern states, using naval forces to stop the flow of supplies. But with the help of American Diver, the Confederate Army hoped to breach the barrier. However, Hunley’s second submarine sank on its way out of Alabama after facing heavy chop. Despite these difficulties, the inventor wouldn’t give up.

Yes, because eventually work began on a third submarine, and in July 1863 the H.L Hunley was unveiled. Capable of carrying eight men, the hand-cranked vessel was armed with a spar torpedo. Now this was a type of explosive mounted on the end of a pole. Additionally, it was equipped with two tanks that could either be flooded or emptied to adjust the ballast of the submarine.

After a successful demonstration, the Hunley was mounted on a railcar and transported to Charleston, SC. However, on August 29, 1863, tragedy struck. And while the submarine’s crew were getting ready to make a test dive, the commander made a fatal error. It was an error that was so straight forward, it was arguably embarrassing.

Apparently, a lever was mistakenly depressed, causing the Hunley to submerge before its hatches were fully closed. And in the resulting disaster, five crewmen lost their lives. Then, six weeks later, the submarine sank during another test – this time killing all eight of the men on board. Tragically, the dead included the inventor Hunley himself. But despite such an ominous start, the Confederate Army retrieved the vessel and put it into service once more.

So by 1864 the Union blockade had been in force for almost three years. And to the Confederate forces, it was more important than ever to find a path through the enemy ships. Therefore, on the evening of February 17, they despatched the Hunley to attack the USS Housatonic. As we’ll find out, this would be no small feat.

Yes, because at more than 200 feet long, the Housatonic was a formidable warship. And it was located just miles off the coast of Charleston. Nonetheless, the Hunley was crewed by Lieutenant George E. Dixon and seven men. And it left its base on nearby Sullivan’s Island, making its way towards the enemy vessel.

Now at first, it seemed the Hunley’s inaugural mission had been triumphant. Using the vessel’s spar torpedo, the crew blew a hole in the Housatonic, sending it to the bottom of the ocean. In fact, this was the first time that a combat submarine had successfully eliminated a warship. But there was more drama to come.

Indeed, and sadly any joy that the Confederate forces must have felt was short lived. For despite its successful attack against the Housatonic, the Hunley did not resurface. And as the hours ticked by, there was still no sign of the missing submarine. Eventually, the next day, reports of the vessel began to trickle in.

According to the commander at the Hunley’s base, the submarine had transmitted signals shortly after the attack. Now logically, this would imply that it was coming back to shore. Furthermore, a surviving crewman from the Housatonic reported having seen a blue light in the aftermath of the attack.And this makes sense as the vessel wasn’t fully submerged by design, and was always only partially under water. But after this sighting however, the trail went cold.

Image: U.S. Naval Historical Center Photograph

So what exactly happened to the Hunley and her crew? Well for some 130 years, the answer remained a mystery. Meanwhile, the Civil War drew to a close, and the wounds of America began to heal. However, the families of the men lost with the Confederate’s pioneering submarine would be left without answers.

In fact, insights into what may have happened on board the Hunley did not begin to emerge until the 1970s. According to Edward Lee Spence, an archaeologist with the Sea Research Society, he located the wreck of the famous submarine in 1970. However, an American court judged the discovery to be out of its jurisdiction, leaving its ownership open to debate. As we’ll find out, though, that wasn’t the end of the issue.

For eight years later, Spence’s location for the wreck of the Hunley appeared in the National Register of Historic Places. However, no further information about the location was forthcoming. Then, in 1995, the archaeologist released book Treasures of the Confederate Coast that included a map of the alleged resting place. Things were starting to heat up.

That’s right, and just three months later there was another development. For diver Ralph Wilbanks discovered the wreck during a dive with the National Underwater and Marine Agency (NUMA). Apparently, it was located some 18 feet beneath the surface in a spot around a mile inshore from the Housatonic. However, leader of the NUMA team Clive Cussler, kept quiet about any connection with Spence’s earlier claims.

And soon, it emerged that Cussler’s initial claims about the location of the Hunley had been inaccurate. In actuality, the wreck was located just 300 feet from the Housatonic, submerged beneath some 27 feet of ocean. Furthermore, it had been coated in a thick layer of silt, which both preserved and concealed the historic vessel.

Now investigators were soon able to confirm that the wreck was indeed that of the Hunley. And on August 8, 2000, a team of researchers banded together to raise the submarine from its watery grave. Using harnesses, they lifted the vessel from the ocean floor and winched it back towards the surface.

Long overdue, the Hunley broke the surface of the Atlantic Ocean for the first time in 136 years. Afterwards, the submarine was taken to the Warren Lasch Conservation Center in North Charleston. There, it was suspended in fresh water so that restoration work could take place. Interestingly, it is now on public display at the center in a museum run by conservationists, the Friends of the Hunley. What’s more, it remains in a water tank to help preserve it.

Image: Friends of the Hunley via Post and Courier

Nonetheless, conservation work on the Hunley continues, and has been slowly revealing the submarine’s secrets. On board, researchers discovered the remains of the crewmen who had gone missing alongside the vessel. Apparently, they were mostly located near their stations, with no indication that they had tried to escape. But that’s not all.

Intriguingly, researchers discovered that none of the crew members had suffered any broken bones during the sinking. However, other forms of injury could not be ruled out as the bodies had since decomposed. So what had happened on the night of February 17, 1864? Well, over the years a number of different theories have been put forward to explain the sinking of the Hunley.

According to one theory, the Hunley accidentally collided with the USS Canandaigua, en route to assist the floundering Housatonic. However, researchers were unable to find any evidence to support this claim. Then, in 2008, something puzzling was discovered. Apparently, the crew hadn’t attempted to pump out any water from the submarine – a typical response to onboard flooding.

Furthermore, in 2018, another discovery was made. Apparently, the blocks that would have enabled the Hunley to quickly resurface had not been released. So why hadn’t the crew attempted to raise the submarine as it sank? According to some, it was because they were probably already dead.

In fact, one popular theory claims that the crew of the Hunley were killed instantly when their torpedo struck the Housatonic. Perhaps they may have been just too close to the ship, putting them in the path of a deadly shockwave. But while there is some evidence to support this theory, the mystery is far from solved.

Then, in January 2019, a team of researchers from South Carolina’s Clemson University made a startling announcement. While doing conservation work on the Hunley, they had discovered something that may have contributed to the fateful sinking. Apparently, there was a gaping hole on the wall of the vessel where a pipe had broken.

According to experts, the pipe was designed to carry water into the ballast tank located at the front of the vessel. However, to do so it had to pass through the rounded hull, bending it out of shape from the start. “You pushed it up and then locked it in place,” Michael Scafuri, a Clemson University archaeologist, told The Post and Courier.

However, when researchers got a closer look at the section of the wreck, they discovered that the pipe had broken. And at the point where it should have attached to the submarine wall, there was a gap approximately one inch wide. But could this fault have been enough to sink the vessel and all of her crew?

Image: IBRAHIM CHALHOUB/AFP via Getty Images

In a statement released on January 14, 2019, the Friends of Hunley explained this theory. “If the pipe broke off the night of the Hunley’s historic mission, it may have contributed to the sinking of the submarine and the loss of her crew.” Moreover, researchers established that as little as 50 gallons of water might have been enough to sink the vessel. And that’s an amount that could have escaped via the broken pipe in just three minutes.

Now, this find was made after restoration workers removed a thick layer of a substance known as concretion. This is a mass of shells, sand and marine life that gathers on artifacts submerged underwater for a long time. And according to those involved, it was a painstaking process. In fact, conservators spent hours working on the submarine in cramped and uncomfortable positions, particularly inside the crew’s compartments.

Image: Warren Weinstein/500px/Getty Images

But according to Johanna Rivera-Diaz, a conservation specialist at Clemson University, it was all worth it. “Removing the concretion was a slow and challenging task for all of us involved, but the ability to get an up-close look at the true surface of the submarine after all this time has made it entirely worthwhile,” she explained in the statement from Friends of Hunley.

However, the University acknowledges that this discovery has not necessarily solved the mystery of the Hunley. For example, it highlighted that the pipe breach was small and could easily have been plugged by something like a cloth. Crucially, though, it remains that the crew had not activated the equipment that would have pumped water out of the vessel.

So if a broken pipe did not sink the Hunley, what else might have happened? Now it’s possible the fixture simply drifted away from the submarine wall during the 136 years on the ocean floor. “More study of this area will help us understand whether it broke off naturally or was sheared off by an impact or explosion backlash during the attack on the Housatonic,” the University explained.

At the moment, however, the evidence remains inconclusive. “Unfortunately, there are no easy answers when investigating what led to a complex 150-year-old sinking,” Scafuri explained. “Still, this is a very significant discovery that will help us tell the full story of the Hunley’s important chapter in naval history.” Indeed, and there was still more to learn about how the early submarine itself interacted with its crew.

Yes, because the broken pipe wasn’t the only thing that experts discovered as they peeled back the layers of concretion. For example, excavations revealed an intricate system of gears that would have maximized the cranking efforts of the crew. What’s more, although the remains of the crew were removed, something else had been hidden by the concretion.

For you see, researchers discovered a human tooth near the station that crewman Frank Collins had likely occupied. The remains of the American volunteer were interred in a Charleston cemetery back in 2004, alongside the other crew members. In fact, they were buried with the earliest submariners of the vessel who had perished during its testing stage.

So today, work is continuing on the Hunley, with experts hoping to learn more about what happened back in 1864. Meanwhile, the submarine remains suspended in water, where it is set to stay for the next five years. After that period, the museum display will likely become permanent, with the artifact dried off for public gaze. But in the meantime, visitors to the Warren Lasch Conservation Center can still view it. More importantly perhaps, they’re able to theorize themselves as to how this Civil War legend met its end.