CSS Hunley Reconsidered

Library of Congress

Conrad Wise Chapman’s painting of H.L. Hunley in Charleston was the only detailed representation of the submarine known to historians until the hull of the hand-powered boat was recovered in August 2000.

What do USS Housatonic, HMS Pathfinder, and HMS Courageous have in common? Each was the first warship to be sent to the seafloor by an enemy submarine during a major military conflict. The carrier Courageous was on anti-submarine patrol when it was torpedoed twice by the German U-29 in the opening weeks of World War II. The cruiser Pathfinder was also sunk by a U-boat, U-21, in 1914 at the start of World War I—the first time in history that a self-guided torpedo sank a ship.

U-21 and U-29 both survived their encounters to fight another day. Not so the submarine H.L. Hunley. The Hunley successfully sank the sloop-of-war USS Housatonic in February 1864 off the coast of Charleston, using a spar torpedo to become the world’s first submersible to sink another ship. But its success was short-lived; the boat and crew disappeared that same evening, initiating a series of mysteries that endure to this day.

The 40-foot-long vessel proved surprisingly elusive over the next 140 years while resting on the seafloor, evading detection by a series of shipwreck hunters. All the while, the enigma of the submarine’s location, the cause of its sinking, and what killed its crew grew substantially. The discovery (1995) and recovery (2000) of Hunley’s buried hull answered the first of these mysteries, but the cause of the sinking and the crew’s deaths remained secret. Finding conclusions to such questions involves a great deal of scientific investigation, a perfect topic for this column, where we focus on how science—in this case archaeology, geology, and paleontology—can be used to interpret Civil War history.

The Hunley was not a good submarine; it was a crew-killer. By comparison: On July 10, 1863, the Union forces on Morris Island, South Carolina, under the command of Brigadier General Quincy Gillmore, launched a calamitous attack targeted at the Confederate sand fort Battery Wagner. The assault resulted in more than 300 Federal casualties, while the Confederates lost only 12 men. A mile or so to the north, and at approximately the same time, Hunley killed more Confederates simply trying to conduct test runs around Charleston Harbor.¹ Even when Hunley entered combat a few months later, the boat was responsible for more Rebel deaths (eight) than Yankee (five).

Library of Congress

William Waud’s sketch “Destruction of Housatonic by a rebel torpedo. Feb. of 17 1864. Charleston.” Hunley embedded its spar torpedo on the starboard stern of the sloop, so that the blast of the explosion would be directed into the underside of the ship. Housatonic settled on the bottom quickly, but in shallow water. Five members of its crew died.

Gillmore was to blame for the repeated failed assaults against Battery Wagner that summer of 1863. Two decades later, by then a coastal engineer in charge of the southern Atlantic region, he would completely obliterate the fort by accident. When Gillmore ordered construction of the massive jetties designed to stabilize the entrance of Charleston Harbor, the direct result was the rapid erosion of Morris Island and all of its temporary fortifications, including Battery Wagner. At the same time, this engineering project diverted sand offshore, directing sediment onto the Hunley’s wreck site. This massive influx of sediment no doubt helped to bury and conceal the boat, but also to preserve it.

When the submarine was finally located and brought to the surface 25 years ago, the scientists who excavated the sediment-filled hull made a remarkable discovery. Most of the archaeology team assumed that some human remains might be found inside the iron vessel, perhaps scattered bones and teeth. After all, the submarine and its contents had been exposed to the harsh currents of the continental shelf for more than 100 years, along with a countless variety of scavenging creatures. Instead, the sediments in the bottom half of the hull held eight sets of complete skeletons, systematically arranged in the submarine, with soft tissue and the remains of intercranial material (brain matter) intact. Such preservation is unheard of for similar undersea sites; RMS Titanic, a wreck 50 years younger than Hunley, has yet to reveal any human remains. What was so special about the South Carolina site that allowed for such an unexpected and valuable time capsule, especially with respect to conservation of human remains?

Twenty years ago I was asked to join a fellow geology professor, M. Scott Harris of the College of Charleston, to help answer this question. Over the last two decades we sifted through thousands of sediment samples and collected tens of thousands of fossils from inside Hunley’s hull, using our training in sedimentology and micropaleontology to provide some insights into the exceptional preservation of the crew and, possibly, the cause of their deaths.²

The sedimentary layers deposited inside the entirety of the hull tell an interesting story, one that might at first appear rather granular. Two dissimilar layers of sediment comprise the majority of the material inside the submarine: clay-rich mud and sand. When the boat first came to rest on the ocean floor, and as the crew’s bodies began to bloat, float, and eventually sink to the floor of the sub, there was probably only one small breach or hole in the hull. This damage was located on the forward end of the front conning tower, where the cast iron has been perforated by an impact of some type.³ Otherwise, the hull was completely intact, limiting the exchange of water (and oxygen) between the inside of the submarine and the continental shelf. As a result, there were eight putrefying corpses located in a relatively small, nearly completely enclosed iron container with little oxygen exchange with the exterior—the recipe for an anoxic depositional environment. Additionally, the impenetrability of the iron hull meant that only the finest of sediment, silt and clay, could find its way to the interior where it slowly covered the men’s bodies. The deposition of this “toxic mud” prohibited scavenging by crabs or worms, because without oxygen scavengers can’t do their work. The combination of low-energy (quiet), oxygen-depleted water and a relatively rapid sedimentation rate was ideal for the preservation of soft tissue.

Sometime after this thick layer of mud had accumulated, almost entirely encasing the crew’s remains, the pattern of sediment deposition changed dramatically. The harsh sediment-laden bottom currents offshore of Charleston slowly etched, then blasted through the hull on the sides of the bow and stern. Water and sand and a myriad of sea creatures began to move into and through the submarine. Sedimentary structures like cross-bedding indicate the flow of water was strong, and the number of fossils present in the sand indicate it was a healthy marine environment. Had the corpses been exposed to this depositional environment when the submarine first hit the bottom, there would have been no human remains to discover.

This shell-rich “healthy sand” was full of creatures such as scallops, sea urchins, starfish, and tens of thousands of microscopic creatures called foraminifera. The sand accumulated until the hull was nearly filled and the openings fore and aft were blocked by sediment. Importantly, none of these creatures from the healthy sand were able to penetrate the underlying dense toxic mud, assuring preservation of the crew. How do we know these layers were “toxic” and “healthy,” especially with respect to the changing levels of oxygen in the seawater from 150 years ago?

Scott Hippensteel

Foraminifera and a diatom collected from the sediment from the interior of the hull of H.L. Hunley. Each of these microfossils is approximately ¼ of a millimeter in size. The diatom is triangular in shape (top); the foraminifera at the center is Bolivina, a taxa that prefers low-oxygen marine waters.

This is where foraminifera (forams) prove to be especially important. These tiny creatures are incredibly abundant (often there will be a few hundred in a cubic inch of sand) and very picky about where they live—different species prefer different water salinities, temperatures, and, importantly for the Hunley study, different oxygen levels. In the muddy bottom layer of sediment surrounding the bodies of the crew, there aren’t many forams, and those present are of a species known to prefer low-oxygen environments. In the overlying sandy sediments the foram assemblages are completely different, and include a variety of species that are common in healthy, shallow-water continental shelf environments.

Microfossils also have something to tell us about the fate of the crew: Did the men suffocate, drown, or suffer some other cause of death? To answer this question, we turn to a second type of microfossil, diatoms. Unlike forams, these tiny creatures are plants. They are also made of silica, so they are especially durable. Diatoms are found in all aquatic environments, in numbers that rival foraminifera. When I surveyed the microfossils from Hunley’s offshore wreck site, I found diatoms in great abundance in the surface waters, all through the water column, at the seafloor, and in the bottom sediments. They were also present in all layers of the sediment from inside the hull. Basically, they were everywhere. Their usefulness in forensics is related to their abundance and cosmopolitan nature, but even more so to their minute size and robustness.

Scott Hippensteel

The interior of H.L. Hunley. Basic layout (A) shows the position of the seven crew members, who powered the hand crank, and the captain. After the vessel’s sinking the interior was completely full of sediment (B). The dashed line indicates the contact between the “toxic mud,” which enveloped the bodies, and the overlying “healthy sand.” Foraminifera (C) were most common in the sand layers, and those species found in the bottom mud were varieties that prefer low-oxygen conditions.

When humans drown, their final act is to reflexively inhale, whether they are submerged or not. If they are underwater, this desperate gasp will bring water into their lungs. If they are in the ocean, like the crew of a submarine, they will inhale seawater—and shallow seawater usually contains diatoms. Once diatoms are in the lungs, they are so small that they can pass through the lung membrane and enter the circulatory system. From here, the microfossils can be distributed throughout the body—to the liver, brain, or other soft tissues.

By contrast, if a person suffocates and is later submerged in seawater, the lungs will eventually fill with water and diatoms, but the heart has already ceased working because of the earlier lack of oxygen. Thus, there is no means of distribution for the diatoms outside of the lungs and throughout the body. In short, if diatoms are found in a corpse’s soft tissue or organs, death was likely caused from inhaling water, not suffocation.⁴

Returning to the fate of the crew of the Hunley, their soft tissue was preserved in several instances. Much of this material is adipocere, a waxy substance that is the result of the breakdown of fatty tissues in the presence of water. If diatoms are present in this adipocere, that might suggest the crew drowned, rather than suffocated inside the submarine. Also, if the adipocere was enriched with diatoms, further studies could search for microfossils in the brain matter, providing even more proof of the cause of death.

Scott Hippensteel

Two diatoms from the wreck-site of the Hunley, imaged using a scanning electron microscope. Each diatom is approximately ½ millimeter in size.

The exact process for extracting siliceous microfossils from adipocere is both delicate and complicated, involving protein digestion and the implementation of several different acids. In the end, diatoms were found everywhere in all environments, even in the toxic mud surrounding the bodies, but they were absent from the adipocere. This suggests, in a very limited way, that the men suffocated inside the hull.

When I give talks about the geoarchaeology of the Hunley, whether to my students or the general public, I am always asked for my opinion regarding the sinking of the submarine and what happened to the crew on the night of November 17, 1864. One thing seems obvious: There was no struggle to escape. The remains of each of the crew were draped across and under the hand-crank and bench at their assigned station in the boat. The bones appear to be almost carefully placed in position—these men were not trying to escape a sinking vessel.

I suspect the crew were concussed by the explosion of the spar torpedo. They were, after all, sitting only 20 feet away from the explosion of 135 pounds of black powder, all while underwater in an iron tube. Once the crew wereunconscious there would be no one to repair the minor bullet damage to the conning tower and the boat may have started to slowly take in water before gently submerging and settling to the bottom—this only a short distance offshore from the submarine’s much larger victim.

In the end, the causes of Hunley’s sinking and of the crew’s deaths remain mysteries. Nevertheless, microfossils from within the hull provide their own tiny clues to the fate of the world’s first successful submarine and, at the same time, rather conclusively document why this time capsule from 1864 has been so exceptionally preserved.

 

Scott Hippensteel is professor of Earth sciences at the University of North Carolina at Charlotte, where he focuses on coastal geology, geoarchaeology, and environmental micropaleontology. He has written four books about using science to illuminate military history: Sand, Science, and the Civil War: Sedimentary Geology and Combat (University of Georgia Press, 2023), Myths of the Civil War: The Fact, Fiction, and Science behind the Civil War’s Most-Told Stories (Rowman & Littlefield, 2021), and Rocks and Rifles: The Influence of Geology on Combat and Tactics during the American Civil War (Springer Nature, 2018). His latest book, Civil War Photo Forensics: Investigating Battlefield Photographs through a Critical Lens, is forthcoming from the University of Tennessee Press.

Related topics: naval warfare, technology