This Issue's Featured Article Nov

Why Did the Hunley Disappear?

From the Hunley Project
With Thanks to Reader Bob Dalley for Alerting us to This

The night of February 17, 1864, the Confederate submarine H. L. Hunley attacked and sank the USS Housatonic off the coast of Charleston. She then mysteriously vanished with her crew of eight. That night, history was made and a mystery was born. The Hunley became the first submarine ever to sink an enemy ship. But why had she suddenly disappeared? What caused her to sink? And would she ever be found?

Lost at sea for over a century, the Hunley was located in 1995 by author Clive Cussler and raised on August 8, 2000. The innovative hand-cranked vessel was delivered to the Warren Lasch Conservation Center, where an international team of scientists are at work to conserve the submarine for future generations and piece together clues to solve the mystery of her disappearance.

The Hunley Project is conducted through a partnership with Friends of the Hunley, the South Carolina Hunley Commission, Clemson University Restoration Institute, Naval History and Heritage Command, and the Charleston Naval Complex Redevelopment Authority.

For more information, call us at (843) 743-4865 ext. 14 or email

Take a Look Inside: The Hunley
Crew Compartment is Slowly Emerging

It is no secret the crew compartment of the H. L. Hunley, the world’s first successful combat submarine, was small. Conservators working to save the pioneering vessel have a new understanding of just how cramped and intimidating it must have been for the eight-man crew in 1864 when they cranked the Hunley into world history. Working in the small confines of the roughly 4’ tall hull, scientists are using drills and small hand tools to slowly break off the concretion, a layer of sand, sediment, shells and corrosion products, that built up slowly over time while she was lost at sea for over a century. The concretion completely masked the original surface of one of maritime lore’s greatest artifacts as well as many of its finer operational features.

“The work can be exhausting, but I love this job. I get to watch the submarine come out of its shell and be one of the first people to actually see the crew compartment in over a century. It is really very exciting,” said Clemson University’s Warren Lasch Conservation Center’s Associate Director and Senior Conservator Lisa Nasanen.

A Look Inside the Crew Compartment

The delicate effort to clean the crew compartment has already yielded some interesting finds:

Human Remains Found

A tooth was found in the concretion on crank position number 3, where it is believed crew member Frank Collins sat. His remains were buried in 2004 alongside his crewmates and others who lost their lives in the testing and development of the Hunley. At the time of his burial, several teeth were missing from his cranium. Forensic analysis of the skull indicated the teeth were lost after his death from decomposition, meaning the discovery of more human remains was not a totally unanticipated find.
Practical Design

The iron crank system was designed to address the vigorous challenges of cranking. Cranking for the length of time needed to reach the enemy target ship was strenuous work and no doubt caused muscle fatigue with blisters and sores. It appears a thin metal tube wrapped loosely around the crank allowed for easier work. The tube was then covered in a cloth material, likely meant to soften and alleviate the rub on the hands.

Operational Discoveries

Cleaning the inside is slowly offering a greater understanding of the vessel’s overall operation. A complex series of features are emerging showing the Hunley’s design was more sophisticated and dynamic than originally thought. The flywheel that powered the propeller can now be seen as a clever piece of engineering. It has a system of different size gears that provided a positive torque ratio to turning the propeller. In another words, the complex gear system helped enhance the output of the crank-generated power, helping maximize the impact of the crew’s hard work.

The Deconcretion Project

Until recently, the concretion completely covered the vessel both inside and out. It is being removed so a conservation treatment can be completed to ensure the submarine is preserved for our generation and the ones to come. It has been a multi-year process with several different phases.

First, the exterior of the submarine was cleaned of this encrustation. Then, in 2016, scientists moved their work to clearing it off the interior. They have started in the forward and aft sections of the submarine. These are the more complicated areas, holding the Captain’s station and key navigational tools such as the tiller, gears and levers that controlled the rudder and dive planes.

Clemson University conservators have been chiseling away this encrustation, collecting samples along the way. They are hoping once the submarine is completely uncovered it will help offer a better understanding of the events that led to the disappearance of the submarine and her eight-man crew.

“We are finally getting to see many previously hidden details of both the hull and the mechanisms the crew used to operate the submarine the night of the attack. These new clues will likely prove essential to our investigation to understand what really happened to the Hunley,” said Clemson Archaeologist Michael Scafuri.

Conservators work in close quarters to clean the interior of the Hunley submarine.

Safety First

Given the extremely cramped confines of their workspace and other challenging logistics, the deconcretion effort has not been going as quickly as once hoped. Scientists follow a sequence that starts with draining the 75,000-gallon conservation tank which holds the submarine. Once the chemical solution is out of the tank, the Hunley must be covered inch-to-inch with a plastic wrap to keep it from drying out and rusting while scientists work. Before entering the tank, the team must gear up with protective body suits, gloves, goggles and respirators to protect them from dust and chemical residue.

This entire preparation process takes approximately an hour before they can even begin to get down to the work at hand. From there, they lower themselves into the submarine wearing a body harness connected to an overhead crane for safety. Then they must stay curled up on their knees or stay in other awkward positions for hours working in the small crew compartment.

The work is physically and mentally exhausting. The focus required to use pneumatic chisels and small hand tools to remove the concretion can be quite stressful. One drop of a tool or slip-of-the-hand or other mistake could cause permanent damage to the fragile, irreplaceable artifact.

Clemson University Conservator and Collections Manager Johanna Rivera-Diaz, “We are moving slowly, but we are moving. The extent of the site preparation and then limited time windows to work on the sub can be frustrating at times. Still, at the end of the day, safety for the team and the submarine must always come first.”

Mys­tery Over­view

Why Did the Hunley Disappear?

The disappearance of the H. L. Hunley is one of the greatest mysteries in maritime history. Shortly after sinking the USS Housatonic on February 17, 1864, the Hunley vanished without a trace. For more than a century, history buffs and adventurers speculated on the legendary submarine’s fate while divers searched for the wreck in the waters off Charleston.  When the Hunley was found in 1995, and then raised in 2000, many hoped the answer would finally be within grasp.

The archaeological examination of the wreck has provided tremendous insight into the pioneering submarine’s operation and offered many clues into the Hunley’s final moments. Still, a complex puzzle has emerged with evidence sometimes creating more questions than answers.  We are closer to discovering the cause for the Hunley’s disappearance, but there is still no clear explanation.

Here, we have a listing of the evidence collected and some possible theories to explain why the Hunley didn’t return after her mission. 

The Evidence

Here is what we know as of now…

Crew Remains

Archaeologists excavating the Hunley after its recovery in 2000 found the crewmembers’ remains largely at their stations, with no sign of panic or desperate attempts to escape the submarine. The remains also show no new injuries, suggesting whatever happened to the Hunley was not violent enough to break the crew’s bones. Since the bodies decomposed more than a century ago, any flesh or tissue wounds the crew may have experienced that night will never be known.

Looking at the forensic data in the 3D model, it becomes visually apparent there was little co-mingling of the remains and each man seems to be resting at his assigned station.

Hunley Location on the Seabed

One of the many reasons it took so long to find the Hunley was because her location was not where most expected.  Searchers usually looked between the shore and the wreck of the Housatonic, assuming she must have been lost between those two points as the submarine attempted to return home.  In fact, she was found on the sea-side of the Housatonic, about 1,000’ (less than half a mile) from the Union ship’s wreck site.

Damage to Submarine

When the Hunley was recovered, signs of obvious damage were noticed immediately, including a large hole in the aft ballast tank. It is tempting to look at the holes and appendages that broke away and assume they are scars remaining from the night of the historic attack. However, most of the damage happened slowly over time while the Hunley rested on the ocean floor for over a century. In fact, much of the damage to the sub is the result of unforgiving underwater currents and scouring sand.

The rudder was found detached and underneath the vessel.  Based on where it was found, lying beneath the keel, it seems the rudder broke off the submarine not long after it sank.

The forward conning tower held five viewports. Captain Dixon used these to navigate and as his windows to the outside world.  One of the viewports is completely missing. There is now a grapefruit-sized hole in its place. Since a broken off iron fragment from the missing view port was found in the sediment at the very bottom of the submarine, this damage could have happened very early, potentially even the night of the attack.

The hatches that sat on top of the forward and aft conning towers served as the only access points into and out of the submarine. Scientists found one hatch was locked and the other was not. The forward conning tower was found unlatched. This could be significant, but the hatch was heavy enough that it would stay sealed while the submarine was underwater and upright. The aft hatch was found locked. If the crew had been desperately trying to escape, it is reasonable to assume both hatches would have been unlatched.

Ballast Pump Settings

When the Hunley mysteriously vanished, most students of history assumed the eight-man crew drowned.  That may not be true. The pumps are still in the same position they were on the night the submarine was lost. Those settings could reveal what steps, if any, the crew may have taken to try and save their lives. A preliminary study of the pump system shows that it was not set to pump water out of the crew compartment.  This discovery suggests the crew may not have drowned, but died of some other cause.

Blackout Mode

The Hunley was in Blackout Mode when she was lost.  The submarine had a series of ten topside ports that provided the crew a small measure of ambient light when the Hunley cruised on the surface. These small glass ports were equipped with iron covers that could make the ports watertight and also block any light from escaping the sub, and possibly alerting ships to their presence.  These ports were all found closed.

Historical Records

Some historical evidence suggests the Hunley did not sink immediately after the attack and light, perhaps in the forms of signals, was seen by both Union and Confederate sources. Records indicate the Hunley crew was to signal to shore if they were successful in sinking the Union warship.

Robert Flemming, a sailor on the USS Housatonic, was standing bow lookout watch the night the Hunley attacked. About 45 minutes after the attack, Flemming, who survived and retreated to the Housatonic’s rigging to await rescue, said he spotted a blue light on the water just ahead of the USS Canandaigua, the first Navy ship to arrive on the scene.

“When the Canandaigua got astern, and laying athwart of the Housatonic, about four ships lengths off, while I was in the fore-rigging, I saw a blue light on the water just ahead of the Canandaigua, and on the starboard quarters of the Housatonic.” Robert Flemming. Flemming’s report of a blue light could be consistent the testimony of Confederates at Battery Marshall, who said Dixon said he would show “two blue lights” when he wanted a signal fire lit on the beach of Sullivan’s Island.

In addition to Flemming’s testimony, we have two others: Lieutenant Col. Dantzler at Battery Marshall reported on February 19, 1864, “The signals agreed upon to be given in case the boat wished a light to be exposed at this post as a guide for its return were observed and answered.” In 1866, Jacob Cardoza recounted, “The officer (Dixon) in command told Lieutenant-Colonel Dantzler… if he came off safe he would show two blue lights. The lights never appeared.”

Was Flemming the last man to see the Hunley for more than a century? If he was, his account could suggest a tragic end for the Hunley. If the submarine was “just ahead” of the Canandaigua, which was sailing to rescue Union sailors, it could have created a wake that toppled the submarine or hit it directly. Also, because the Hunley had no ports facing aft, the crew might not have even known a ship was bearing down on the submarine.

Sediment In-filling

After the Hunley filled with water, sediment suspended in the water column settled along the bottom of the submarine.  Analysis of the deposition of sediment indicates some additional material filling the submarine over time may have entered near the forward conning tower.  The breach in the forward conning tower is the most likely source, and would explain some of the courser sediment discovered in early deposits at Dixon’s station.

Top Possible Theories

What do you think caused the Hunley to sink? Torpedo explosion? Trapped by the tides? Collision at sea?

Bottom of Form
The Hunley became the world’s first successful combat submarine when it sank the USS Housatonic on February 17, 1864. Once the torpedo had detonated on the Housatonic, the submarine signaled to shore she had completed her mission and was on the way home. Confederates on shore lit a fire to help guide the submarine back to land, but instead, the Hunley disappeared into the sea. We may never know exactly what took place on that fateful night, but over the course of the last 150 years, there have been plenty of theories.

#1: The Torpedo’s Explosion
Cripples Hunley

Perhaps one of the most obvious and popular theories is the explosion that caused the Housatonic to sink also crippled the Hunley by damaging the submarine or incapacitating the crew. This could very well prove to be the cause if the Hunley was too close to the torpedo when it detonated, which recent findings show was only about 20’ away. Being this close could have caused damage to the sub, causing water to come rushing in, or the concussion could have knocked out the crew.

This theory was further advanced when the Hunley was recovered with several large holes in its structure visibly apparent; however, we are now learning that this damage was caused by Mother Nature. It appears most of the breaches happened a long time after the night of the attack due to the hostile underwater environment and the abrasive effects of the tides.

To account for the fact that no evidence was found to suggest the crew was desperately struggling to exit a damaged submarine to avoid drowning, the concussion theory still holds water. In this scenario, the torpedo’s explosion didn’t damage the submarine but caused a concussion strong enough to stun or knock out the crew. This would have rendered them incapable of immediately navigating home, possibly leading them to perish due to a lack of oxygen or through the inability to take any steps to save their lives.

#2: Trapped by the Tides

Manually cranking the 40’ submarine to its target over four miles offshore was hard work.  To help offset the physical difficulty of the task, we know the Hunley crew carefully planned their mission with the tides.  On the historic night, the submarine departed and rode with the ebb tide.  After the attack, the crew would certainly have been exhausted and in need of rest while waiting for the tide to assist them on the journey home

It is possible that they settled on the bottom of the sea floor to wait for the tides to shift while also avoiding potential detection and gunfire from other Union ships quickly closing in to rescue Housatonic survivors.  While submerged, they may have miscalculated their oxygen supply and died of asphyxiation or while trying to return for some reason, the submarine may have gotten stuck on the ocean floor and unable to rise to the surface.  This theory is supported by the placement of remains in the submarine and at least one exit to the submarine being locked and sealed shut. Also, a cold front causing a storm system moved through that night around the time of the attack, meaning it would have been much more difficult to crank the submarine back to land.

#3: Collision at Sea

The Housatonic sank in shallow waters and many of the crew climbed up its rigging to wait for help.   The first ship on the scene was the USS Canandaigua.  During the subsequent Union inquiry into the Housatonic’s loss, one of its survivors, Robert Flemming, offered the following testimony: “…while I was in the fore-rigging, I saw a blue light on the water just ahead of the Canandaigua and on the starboard quarter of the Housatonic.” Blue lights were the Hunley’s signal to shore that her mission was successful.  Fleming’s testimony suggests the Hunley did indeed survive the mission.

However, if the Canandaigua was moving quickly to get to the scene, she could have clipped the Hunley in passing. The impact created may have been undetectable by the Canandaigua’s crew, but deadly to the Hunley. The damage could have caused the Hunley to take on water or else to lose balance and tumble to her demise.

After seeing the surprise explosion, all the Union ships blockading Charleston Harbor hurriedly moved in to rescue survivors. The massive movement of ships would have created large wakes, adding tremendous volume to the already choppy waters off the coast of Charleston. The water displacement could have been hazardous for the Hunley.

If Dixon opened the forward hatch to replenish oxygen or to display the blue light signal, a large swell or wave could have swamped the vessel. With too much water onboard, the submarine could have been thrown off kilter or lost buoyancy.

#4: Lucky Shot

We know the crew had a candle onboard for visibility and to help monitor oxygen levels within the sub.  They also had glass portholes along the top of the crew compartment and in the conning towers. Aware that any light emitting from the submarine could alert the enemy to their presence, the Hunley was prepared to go into “blackout” mode where all view ports would be covered. However, the forward conning tower’s view ports were used by Captain Dixon for navigation. It would have been necessary for him to leave at least one port open so he could see outside to conduct the attack. A light gleaming through that one window may have provided a bull’s eye target for Union soldiers.

Records tell us Housatonic sentries spotted the Hunley shortly before the attack and opened small arms fire on the vessel. The fragile glass in the view ports was one of the most vulnerable areas of the submarine. The Lucky Shot theory speculates Dixon himself may have been hit by gunfire through the glass port. Without a captain and with water entering the submarine from the shattered glass viewport, the crew may have been unable to make their way home.

This theory is supported by the fact that the only viewport missing from the entire submarine is on the forward conning tower by Captain Dixon’s station. Also, scientists have discovered the damage to this area happened early, perhaps on the actual night of the attack in 1864.

However, forensic analysis of Dixon’s skeletal remains show no damage to the cranium or any other active bone wounds for that matter. But this does not rule out the possibility of wounds to soft tissue that may have incapacitated the captain. Perhaps most importantly, no bullet has been found within the submarine.

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