My adviser had a saying: You have to believe that Sisyphus was happy. It was a reference to the grind of research—weeks of preparation, building anticipation, and careful execution—that often ended in failure.
—Justin Chen, Coming to Terms with Six Years in Science: Obsession, Isolation, and Moments of Wonder
The rubbery tentacles of my bundle of cables stretched down the empty hallway of the Duke blast test building. At the end, the underwater blast gauges were still connected and lying on the floor like the flaccid limbs of a beached giant squid. I sat on the cold concrete staring at them, willing them to speak to me. They stayed stubbornly quiet. They had stayed stubbornly quiet through the second day of testing too, consistently giving me nonsensical readings that were nothing more than hushed, jagged burps of noise.
The unseasonably good weather had left us after the first day, and our spectators with it. My mother had watched from a hiding place, protected by a heated seat inside her car as Luke and I had crouched outside over the perplexing gauges. My dad had stayed huddled in his folding chair across the pond, buried in his coat like a bird trying to compress itself into the smallest, warmest ball possible.
Luke and I had taken apart and checked each connection for water, every time finding nothing. We had carefully painted each junction with a waterproof rubber coating anyway, just in case. They had drip-dried inside the makeshift shelter of a cardboard box that the day before held a bulk-sized stash of snack foods, now dumped unceremoniously in the trunk of my car. I had held my coat open to shield them from the wind that blew unimpeded across the fields, to keep them from clanging together as they dried, and at one point I had watched as the vicious wind blew a Phillips-head screwdriver across the wood planking of the pier. Oklahoma had nothing on Pitt Farm in the early spring.
And still, despite all the love and attention, the highest pressure that the gauges had reported was barely a whisper. Explosions make pressure waves; I was still fairly sure of it. But in science, if you didn’t measure it, it didn’t happen.
Back in the lab, the gauges perversely insisted upon working flawlessly every time. They measured each and every pressure loudly and clearly, in sharp contrast to the way they had performed for me in the field.
I rebuilt my assembly inside the lab exactly as I had used it at Pitt Farm. I set the generator up outside and routed the cables in through the doors; nothing was connected to the power grid, just as it had operated at the pond. I sat, psychically willing, mentally screaming at the gauges to fail for me with each systematic alteration of every single element of the setup so that I could finally replicate and thereby explain their mysterious lack of performance. I stayed up until three in the morning laser-cutting more and more Mylar membranes to equip the hungry driver of the shock tube, and when nobody else was free to help with the tests I started dragging Nick to the lab with me to serve as my mandatory “second person for safety” in case of unforeseen testing disasters.
Nothing replicated the failure. The navy-built gauges staunchly refused to give up the secret. Now they worked with expected military precision for every single test.
As I sat on the hard floor, wrapped in a down coat with my hands still stiff from the cold, I absentmindedly flicked one gauge with a pen, as I had been taught by navy gauge guru Kent Rye. With each flick, a perfect pressure spike appeared on the laptop screen. Flick. Spike. Flick. Spike. Frustratingly perfect.
I had only one idea left. It involved the long cables underwater. I wasn’t sure it would work. And it would have sounded crazy to anyone who was not an engineer.
Stretching thousands of kilometers underwater, the first transatlantic telegraph cable was completed in 1858, years before Hunley, McClintock, and Watson began their mechanical underwater experiments. It allowed communication between Newfoundland and Ireland in seconds rather than weeks, and it signaled a mammoth technological leap forward for humanity.
Laying the cable down through the hostile, turbulent ocean and splicing the various behemoth sections together to complete the connection was a historic feat of engineering. It spanned decades, consumed uncounted thousands (if not millions) of hours of labor, and required the development of dozens of radical engineering and scientific innovations. Engineers had to design ways to deal with waves, with weather, with the crushing pressures of the ocean depths, and with the trials of coordinating the meeting of two boats in the middle of the Atlantic long before the invention of the radio.
They also had to deal with the fact that cables, especially underwater cables, tend to bleed. The lifeblood of a conventional cable is electricity. Electrons travel down the metal wire inside the cable’s protective coating, tumbling from a higher-energy state at the source end to a lower-energy state at the far side, and creating an electrical current along the line with their motion. But the cables can bleed electrons. Not as human beings bleed, through a wound or a fissure; rather, as a slow and usually negligible ooze that occurs down the entire length of the cable. The electrons strongly prefer to travel neatly down the highly conductive metal, but nonetheless some deviants manage to seep through the walls of the less-conductive insulation.
Most of the time, this ooze is so minuscule that it can be ignored. But if the cable is long enough, or placed in a highly conductive material like water, or in a cold enough environment, then the seepage of electrons can make a difference. As a result, by the time an electrical signal reaches its goal, that signal is dramatically reduced in magnitude. The voltages, which started out large, get reduced to almost nothing by the time they reach the other end of the line. In my case, this would result in measurements of abnormally tiny pressures.
The transatlantic cable, thousands of kilometers long, buried deep under cold, highly conductive salt water, oozed so substantially that it required the development of new methods of protection against the bleed. The cable was eventually insulated by painting it with layer upon layer of gutta-percha, which is essentially a tree sap that dries into a sort of rubber and is sometimes referred to as “natural latex.” The ingenious engineers on the project didn’t leave the insulation to chance either; they developed an equation and they mathematically modeled the seepage. They called it the cable equation.
Sitting splayed out near the blue tendrils of my dead pressure-gauge squid, I scribbled my way through the cable equation. When my cables were submerged, with meters upon meters of looping gauge lines drooping just beneath the surface of the frigid pond, I concluded that yes . . . these cables very well could be bleeding out a substantial portion of the pressure signal.*
In the 1800s, engineers painted their cables with gutta-percha. But in 2016, I had the advantage of Styrofoam. Using my favorite long black pieces of foam pipe insulation from the hardware store—once again it didn’t matter what diameter, but I will never again say that out loud—I bundled the cables tightly inside and wrapped them generously in bandages of heavy waterproof tape.
The thick, black foam sausage floated in a line from the pier to the center of Pitt Pond. We had already failed twice, still measuring almost nothing, and we had pulled the model boat out of the water as a result. I had dubbed her the CSS Tiny one late night at the lab, and stenciled the moniker onto her stern. She was sitting back on the shore this time, and the goal of this experiment was simply to measure the waveform from the black powder charge that was floating in the pond water, suspended from a chunk of foam pool noodle.
Brad and Luke huddled on towels in the grass while I crouched at the end of the pier, staring at my equipment. Nick sat with them, having been relieved of his assignment pulling the boat back and forth from the folding chair across the pond.
“THREE!” Brad yelled. “TWO! . . . ONE!” He depressed the second button on his setup box to set off the charge. When I saw the plume, I smacked the key to manually trigger the data recording and held my breath as the acquisition box whirred away, processing numbers.
The waveform on the screen was small. Bigger than before . . . but still far, far smaller than I expected. But this time it was smooth! The wave had a beautiful shape, a clean rise, and a visible decay. Gone were the jagged and unpredictable spasms of signal noise that I had previously measured. It still didn’t seem correct, but it was progress.
Brad, Luke, Nick, and I sat together in the grass on the shore to regroup and think through our next steps. Luke snacked on a bag of Cheetos he had fished out of my trunk.
“What if it’s the charges?” Brad suggested quietly. “The plumes have been smaller than I expected.” I nodded. He had to be right. It made sense. We had carefully eliminated all the other variables.
We had placed the gauges in the water first this time, and I had swum out to tap them, both before and after. They had worked; we were cleanly sending signals from Newfoundland to Ireland.
“You know, I talked to one of the explosives agents at the ATF,” he continued, “and he said he wouldn’t technically classify our science tubes as bombs if he found them at a crime scene. They would be too weakly confined to do real damage.”
I turned my head to look at Brad, slowly. Standing up, I walked toward the water, dropping my towel and heavy coat, and kicking off my flip-flops on the way. I waded until the freezing water reached my hips, then began to swim. The bottom of the pond was smooth; my bribed-with-chicken friends and I had verified it. It was man-made, and mostly free of other debris. I took a breath, squeezed my eyes shut, and inverted, hitting the shallow, even bottom with my hands after one swift kick. Kicking to stay submerged, my fingertips ran over the smooth, soft muck until, eventually, they found what they had been groping for: the jagged edge of a piece of copper. Surfacing, sucking in fresh breath to combat the rising levels of CO2 burning in my blood, I hurled the metal onto the end of the pier and flipped back down for another dive.
Like the ribbons of peeled-back copper attached to the spar of the Hunley, we could tell what happened to our charges based on their remains. And shard after shard, every piece of copper I recovered told the same story. Their bodies had bloomed open cleanly along their seams, always starting on one side, more than likely the side of the charge that held the triggering squib.
Our charges were peeling open from one side before the black powder had fully deflagrated, so at least some of the moisture-sensitive powder was getting wet before it could burn and contribute to the explosion. Furthermore, we hadn’t been measuring the pressure created by black powder ripping open sheets of solid copper. We had been measuring the pressure created by black powder fracturing a much-weaker seam.
Everything always seems so obvious once you finally learn the answer. The confinement-sensitive black powder was breaking open the charges at their weakest point, like a chain with a bad link. The pressures from the slow-burning deflagrating explosive, at least from the fraction of powder that even had a chance to burn, were being released before they could grow to any kind of furor. We were building charges one measly step stronger than sprinkling the powder on the open ground and letting it burn harmlessly.
Former army man Luke nudged the shiny pile of shrapnel gently with his toe, popping another Cheeto into his mouth before he spoke up.
“How far do you think we are from the nearest hardware store?” he asked, licking fluorescent orange dust off his thumb. “I know some tricks from Iraq.”
This book is not a bomb-making manual. Even though much of the information can already be found online, Brad, Luke, and I have all agreed that we will never be an active part of its dissemination. Just like I omitted or was vague about some key steps in the manufacture of black powder, so too will I leave out the most effective methods for building weapons of destruction.
Instead, because I am a gear head, I choose to describe our “science tubes” as cars. The Hunley packed a Ferrari. Its relatively thick-walled copper torpedo was a stock Ferrari, one that still had to obey emissions laws and street-driving regulations, but a Ferrari nonetheless. Our sad little tubes, so willing to split open and vomit out their partially burned contents, did not even merit car metaphor status. They were ancient, neglected Schwinn bicycles, with flat tires and rusty chains. To make this project work, our test team needed to upgrade its ride.
Luke and I jumped in my car, all too comfortable with the idea of walking into a reputable place of business smelling like runoff water and algae. Farmer Pitt pointed us toward a local hardware store, one much closer than any of the major chains that would show up on our phones, and we took off.
The hardware store had one visible room, and only a few feet inward from the door was a broad, high counter that blocked access to the rest of the building. On the left was a pegboard with what seemed to be the most commonly purchased items: an assortment of rolls of different types of tapes and the equipment most often needed for fishing. As we entered, a large, well-cared-for German shepherd with a jet-black face and a glossy coat lifted his head from his dog bed behind the counter and let out a single authoritative woof.
The proprietor of the shop appeared in response, a gray-haired North Carolina native. He asked us for our list, then disappeared into the back of the store. The shepherd stared at us alertly the whole time he was gone, never once shifting a muscle, never once breaking eye contact. The dog was the real owner of the store. We paid for our bag of supplies with cash, made sure we were extra polite to the human being who fed the owner, and then went back to the pond.
The Confederates too went through multiple design iterations when crafting their torpedoes. And naturally, it was “bomb brother” Gabriel Rains who led the charge for them, pun intended. He became the master of tinkering to optimize each design for its purpose, balancing the needs of buoyancy, method of placement, and trigger design to maximize both reliability and destructive potential. Living as the Charlestonians were, with restricted supplies, Rains and his stable of roughly thirty-five torpedo-makers became masters of repurposing, often retooling wooden beer barrels, copper turpentine stills, and even tin soda-water fountains to build a potpourri of weapons for the defense of Charleston Harbor.
Everyday wooden barrels were converted into silent warriors that hid just beneath the surface of the water, floating on long lines connected to anchors, waiting for the keel of an unsuspecting Union vessel to scrape over them. The metal-banded wood structures provided positive buoyancy, ensuring they would stretch to the end of their tethers. Rains knew that to maximize destruction, the torpedo should be just below but in direct contact with the bottom of the target’s hull.
The experimenters even took advantage of repurposed chunks of one of the aborted transatlantic cables, having somehow squirreled it down south before the war. It was used to run long lines out to an electrically triggered torpedo 2 miles from shore so that a spotter could initiate the explosion at the exact right moment to destroy a ship. But the cabling proved an unreliable method, and Rains warned against that tactic in the future. It may have failed because the cable was damaged or because it was from an earlier generation of insulation attempts, but for whatever reason the electrical signal bled out into the water and was too weak to trigger the bomb when the button was pushed. In Rains’s words, the voltage “had passed through the gutta percha coating rather than go the distance required.”
Rains and his crew also built some explosive charges with casings of iron, similar to the land mines he was churning out by the thousands, some of which had 2-inch-thick walls. But these proved too heavy to be practical in water, requiring an air space above the powder inside to make them float. The blast experts of the time, aware of the needs of confinement, knew this would result in less power: “When powder was burned in a space occupied by itself it gave a pressure four times as great as when burned in double its own space.”
Tin torpedoes were lighter than iron but stronger than wood, good for deeper immersion, and careful attention was paid to their construction in order to resist the crushing pressures of water. The conical shape and rounded ends of the most common torpedo designs were important, claimed Rains, and even though materials were scarce, “the thicker the tin the better to resist the pressure of water.”
The same was true of the thickness of copper torpedoes. And copper had the distinct advantage of being resistant to marine growth. Barnacles and sea life find it difficult to penetrate to create a foothold, and copper is still frequently utilized as a component in modern paints and coatings for the underbellies of ships. Rains was aware of this material property and used copper for torpedoes that were going to spend long periods of time underwater, so that marine growth would not interfere with the sensitivity of their triggers.
Rains made no effort to hide his distaste for the torpedo boats. He famously refused to be involved with them. He seemed tired of seeing new but always-unsuccessful attempts, writing that he had watched ambitious men build a “thousand and one” failed designs, and referring to submarines in general as “abortions of inventive genius.”
The boats, he thought, often suffered from one fatal flaw: “much danger from their proximity of destructiveness viz the exploding torpedoes.” The spars were suicide, he was convinced, and the only way to use a torpedo boat “safely is by detached torpedoes.”
To cause structural damage to an enemy ship, he was repeatedly insistent that the torpedo had to be immediately below and in direct contact with the hull; off by a few feet, and he asserted it was unlikely to cause any damage at all. In the detailed handwritten textbook he left behind to document his knowledge, he wrote clearly that this insistence on direct contact was “the secret of my great success with torpedoes,” and then he underlined the words. However, for submarines to be safe, he stated that they should be not just a few feet away from their torpedoes, but a few dozen feet away. Rains believed the spars needed to be much longer than the short poles planned for use by the submarine crews, a minimum of 40 or 50 feet long to ensure safety.
Trying to advocate for submarine safety, Rains performed careful calculations on the shape and type of charge that could be attached to such a long spar without being too positively buoyant and pulling the bow of the boat upward, or too negatively buoyant and pulling it down. Despite the fact that he was the Confederacy’s premier expert on underwater explosions, despite the fact that he was the one responsible for peppering Charleston Harbor with 123 infernal torpedoes, his ideas were rejected. The Hunley was fitted with a 16-foot spar, less than half of Rains’s minimum recommended length.
It is tempting to read Rains’s concerns about the spars and eagerly assume he was agreeing with the theory that the blast propagated through the hull. Unfortunately, Rains did not write down why he was concerned. There are many things to be concerned about when a person is too close to a bomb, and blast transmission is only one of them. Therefore, while his statements are consistent with the theory of blast transmission, from the perspective of an objective scientist it is impossible to conclude exactly why he so feared the use of spar torpedoes. Again . . . scientists are the reason that gravity is only a theory.
The Hunley received a thick-walled copper torpedo. Metal so that the torpedo would not be too positively buoyant. Iron was avoided so the powder could be packed tightly. Copper to resist marine growth. Thick metal walls with robustly sealed seams to resist the crushing pressures and water intrusion of ocean life. A torpedo designed to survive until the final journey, but also, accidentally, a torpedo designed to maximize the ripples of pressure that it would send backward through the salty ocean toward the belly of her carrier.
Our trip to the hardware store yielded some glorious pressure traces. We very, very safely and carefully worked our way through Luke’s bag of tricks, starting out small with the modifications that converted our busted-bicycle charges into rusty 1980s Yugos, and working our way up slowly to the modifications that gave us base-model, four-cylinder, harshly used Mustangs with scratched-up plastic wheel covers.
With each charge modification, the pressures in the water increased. And the rise time, that crucial measurement of the amount of time that it took to get to that maximum pressure, shortened. We watched the pressure waves develop one step at a time from harmless, low-amplitude, gently sloping hills into aggressively steep, lethal mountains. We were proving what had already been reported in dozens if not hundreds of academic papers on black powder: Confinement works. But this time, it was our experiment. We made it work. We had finally fixed this part of our experimental setup.
We had to wait almost another month before we could put the boat back in the water with our new-and-improved charges. We had burned all the daylight allotted to Pitt Pond for that day, and Brad had a long line of heroin dealers that he needed to chase before he could come back to volunteer more of his time.
During the break between test days Nick insisted that he and I have a rare night out, to celebrate my upcoming birthday. We showered off the pond smell and put on clean clothes. I mustered the energy for makeup and jewelry. We ate expensive steak. He suggested a beer to round out the night, and we wound up at the local brewery where we had first met. Our friends were there, a surprise, and we laughed together over rich chocolate birthday cake. Nick stood to make a speech. He kneeled. He had a ring. I cried. My strongest memory of any of the words spoken is the “HOLY SHIT!” yelled in surprise by the lab mate seated next to where I stood. We were happy, and our shocked friends snapped pictures of our tear-streaked smiles.
The next day, my birthday, I took a day off work. We sat together on a bench in the warm sunshine. An arm close around my shoulders, Nick explained happily that he had been thinking about this for a while. He had picked now to show me that he was with me through anything. Through fourteen-hour or longer workdays with uncertain access to food. Through hundreds of workdays straight with no breaks. Through hearing a noise at three or four a.m. to come out and find me in the family room, sitting on the floor, cloaked in blankets, hunched over my laptop. He had already ordered me an inexpensive rubber ring, a thin purple band of silicone that I could wear in the pond. I smiled and said thank you. It was thoughtful, and he meant it with love.
Graduate school is notorious for killing relationships; he was a good man, and it had somehow strengthened ours. But inwardly I cringed, mortified and shredded by how thoroughly this soul-consuming project had crept its tendrils into even the most private features of my life.
By the time we could resume testing we were well into June. The South had remembered it was supposed to be a hot climate, and the weather finally agreed with spending all day wet and unsheltered.
I optimistically put the CSS Tiny back in the pond at Pitt Farm when we finally returned, complete with a modified charge. Nick, taking the station across the lake, hauled it into the center of the water. Just beforehand, Luke and I tested it as we always did, by giving it a good solid thwack with a rubber mallet, square on the bow near the internal pressure gauge. I watched the squiggly line of the gauge jump in response.
Brad gave his countdown as usual. I saw the plume of water first, then felt the wood of the little pier shudder beneath my feet in response, before hearing the explosive rumble last of all. I listened to the data acquisition box whir as it processed.
The pressure wave in the water was beautiful, exactly as predicted. And this time, there was a small, jagged jump on the pressure gauge inside the boat. It didn’t look like a normal blast wave. It lasted less than a millisecond, a fraction of a moment. It was barely there. The same nearly negligible squiggle kept happening over and over again, with every test. After the charge modifications, the plumes of water were much larger, more consistent with what I had been expecting. The in-water pressures were finally making more sense. My entire theory might be wrong. Or . . . maybe my setup was still wrong?
I offered to drive back from Pitt Farm so that Nick could nap after the long day of helping me, but he was atypically insistent on taking the wheel. As I settled into the passenger seat of his black Jeep, cocooned in dry towels and prepared for a cozy ride home, he shoved his cell phone toward me.
“Call your mom,” he insisted.
“Why?” I was confused. I wanted to relax a minute first, and we had a long drive back.
“I don’t know. She said to make sure I drove and to have you call her right away.” He looked concerned. All of the alarms simultaneously sounded in my head.
When she picked up, I could hear the tears in her hello. I could hear her stammered breath as she struggled to find her next word, but through the uneven silence I could already guess what happened. My mother does not cry easily.
“Did Grandma die?”
“Yeah,” she responded slowly. Then, immediately, with the concern of a mother: “You’re not driving, are you? I told Nick not to let you drive because I knew you would be upset.” She had known it was a test day, but she hadn’t wanted to distract me from my experiment. My father was out of town. She had spent the day at home, sitting alone in the empty house, waiting for me to finish so I could call.
Nick and I spent the rest of the drive back in silence. My grandmother had been a constant in my life, an unwaveringly warm and happy presence. An immigrant from northern Italy, she had lovingly taught me the best parts of that half of my heritage, pointing out buildings around Detroit that had terrazzo floors laid by my cousins—every relative is a cousin when you’re Italian—and showing me how to hand-shape fluffy gnocchi with perfect ridges.
When we pulled into the crunchy gravel drive at Duke, though, the equipment still had to take priority. There was no time for emotion until later. These tools, now dirty and sopping wet, were my only engines to keep moving forward toward graduation. Before I could go home and pack to leave for the funeral, Nick and I had to sit on the grimy linoleum of the Duke blast test building and carefully hand-dry then lay out every gauge, tool, and cable.
The long trips to Pitt Farm were becoming a problem. Each morning began with loading at least two vehicles, an hour-and-a-half drive, then unpacking and setting up the roughly 600 pounds of equipment. It cut into the day. I needed to be able to complete more testing, and faster, to try to work out the rest of the kinks in my setup. I wanted to find a location on campus where I could set up and use a shock tube underwater to execute more trials rapid-fire, to blast my scale model repeatedly but without investing the time necessary to safely and properly use live explosives.
When I returned to campus, I found myself staring across a featureless wood-veneer desk at the second man I needed to give me access to a body of water, just like Bert Pitt before him.
Darin Smith looked back at me. He worked on campus at Duke’s Chilled Water Plant 2, or CHWP2 to those in the know, a facility that accomplishes a surprising amount more than its mundane name reveals. Duke’s campus hosts a picturesque reclaimed water pond that fills with rain runoff from around campus, complete with carefully planned plant life and well-manicured walking trails. I had been eyeballing it for weeks, hopeful that Duke would let me put my shock-tube driver and boat in there among their fancy wooden bridges and piers.
The pond was not just decorative; its water was the source of cool air for a substantial part of campus, and the plant where Darin resided—this is not a joke—turned the pond water into air-conditioning using a massive, glittering indoor waterfall. The Willy Wonka jokes practically wrote themselves. Luckily, Darin turned out to be just as amazing as his facility.
“This is awesome,” he said. “I need you to write me up a one-page explanation of what you want to do that I can take to my bosses. I can’t promise you anything yet. But I think they should be all right with it. . . . Leave out the word ‘explosion.’”
The powers-that-be acquiesced. They had two conditions. The first was that life jackets must be worn at all times by personnel swimming in the deep, opaque water. The second was a noise test: setting off a shock tube in the water to measure the decibels heard in the air. They wanted assurance that the sound levels would be safe. The tank tests and blasts at Pitt Farm had been relatively muted, so I eagerly agreed.
I built a metal frame to hold the shock tube in place, and my plan was to sink it in the pond and use the noise test as a trial run to see how well the frame braced the shock tube. A small gaggle came to witness the excitement. The project had apparently generated some buzz, which, combined with the gorgeous sunny weather, meant that a crowd of roughly eight guys had wandered down to the pond to stare at me while I struggled to get this experimental setup to work perfectly on the very first try. One of the lab’s undergrads, Matt Udelhofen, had volunteered to sacrifice himself and jump into the murky pond water with me.
The moment I took my first small step into the water I knew Matt and I were in trouble. The toe of my neoprene boot plunged through the deceptively solid-looking pond bottom like an arrow, and with a pathetic squelch, first my foot and then my entire calf got swallowed by the spongy, greedy mud. I watched Matt struggle futilely beside me while I also continued to sink, my legs soon jailed in place by mud shackles, both of us hunching over to avoid being buried above the waist. The life jackets mandated by Duke Safety saved us, and painfully we forward-clawed our way through the putrescent green-filmed molasses until we reached water deep enough to flip on our backs, strap on fins, and kick while keeping clear of the mire. The group watched our comic flail from start to finish while standing on the dry, clean perch of a wooden platform.
The metal frame would—in theory—sit on the bottom of the pond, allowing me to lower the shock tube down onto it with ropes for each test. Since I could not see through the water, I could then set off the shock-tube driver with reasonable certainty that the frame had kept the driver in the correct location. I had given it a broad base on long struts, anticipating some degree of mud, but in this watery sludge not even the most well-designed base would keep it from sinking. Matt and I used an air-filled float to keep it at the surface until we moved it into position.
The frame, as predicted, plummeted unceremoniously with nothing more than a sad burble the moment we let it loose from our hands. With my feet, I could reach down and feel the top few aluminum bars protruding helplessly out of their muddy grave, like the stubbornly upright rigging of a dying shipwreck. I would pull it out eventually at a later date, dangling from the underside of the wooden bridge that marked its gravesite and hooking it with my feet to help the float heave it free from the mud, but for now it was lost.
While we swam, the fish of the Duke pond began to make their presence known for the first time. The introductory nibbles seemed innocuous, but those cautious pioneering fish summoned a swarm of their more aggressive brethren, and soon they tried to consume Matt and me. While struggling with the frame we could not stop moving, or we would risk losing our legs to the bass. I tried not to think about how they coincidentally shared a name with my adviser, Dale Bass.
Matt and I finally gave up. We crawled our way back out of the ooze, abandoning the buried metal frame to the mud gods. We simply dropped the shock-tube driver into the water on a rope and set off the blast. It swung wildly, in a way that would not work for the actual testing, but we were able to get a noise measurement. As the thoroughly entertained but amiable crowd removed their earplugs and took their hands off their ears, the man holding the sound gauge started chuckling. The sound from the blast, he explained, had been three decibels quieter than the rumble of a bus that passed by the pond moments before.
The frame may have been lost, but we got approval to conduct the tests. Overall, it was a victory. Matt and I scraped off as much of the greenish-gray mud as we could and, squelching in our neoprene boots with every step, walked triumphantly back to the lab.
The torpedo of the Hunley too was surprisingly quiet. “There was no sharp report,” stated one USS Housatonic crewman of the blast that sank his ship, with another saying, “I heard a report, not very loud, a low stunning crash, a smothered sound.” A third crewman, presumably belowdecks, only learned of the explosion when he noticed the rising water sloshing around his ankles.
The interface between the water and the air provides an efficient reflecting surface. Meaning, when the underwater blast wave reaches the surface and hits the air, much of the wave gets reflected back down. The amount transmitted into the air above is therefore much smaller than the amount that was traveling through the water, and as a result the sound heard in the air is surprisingly quiet. The waves can travel for miles underwater, but once they are transmitted into the air they are deadened, muffled by the interface.
We began testing at the reclaimed water pond immediately. I decided to turn the mud into an advantage, and built wooden rails to hold the shock tube in place. At their top ends, the long, almost-vertical rails were braced against the footbridge, where we scattered our test equipment. The bottom ends were sunk deep into the muck that had so strongly encased my legs. They held firm. We could stand on the footbridge and slowly lower the driver down the rails like they were a miniature slide.
The shock tube performed beautifully. The pressure would build up behind the Mylar membranes until they ruptured, creating a sharp boundary between the ambient-pressure water and the high-pressure helium. That boundary propagated outward, pushed by the high-pressure gas, and developed into a shock wave in the water. The driver consistently sent shock wave after perfect, infinitely sharp shock wave into the water and toward the CSS Tiny. We could use this setup to figure out what was wrong, why my setup still didn’t seem to be working, and then head back to Pitt Farm to repeat the feat with black powder.
After each blast, two undergraduates would haul the heavy driver out of the pond on ropes, remove the bolts with an impact wrench powered by a generator, change out the Mylar membranes, and slide it back smoothly down the wooden rails. The proximity to campus meant that more undergraduates were available to help, and they soon became my soft-spoken saviors. Undergraduates have often been the unsung heroes of science.
And yet, the blasts resulted in nothing but a slight jiggle inside the boat, no matter how I tried the configuration. Each time we would test the gauges by hitting the boat’s bow with a mallet, and each time the gauges would work fine beforehand but fail during the test.
I was open to the idea that my theory was wrong, but the readings still didn’t make sense. Some degree of pressure transmission through the hull was almost inevitable. Even if the magnitudes were too small to be lethal, and the data didn’t support the theory, the internal gauges still should have been measuring pressures of some kind that had resulted from the shock waves in the water. Their relative silence told me they weren’t yet working as they should.
Slowly, the undergrads began to avoid me in the hallway, rationally more eager to help with projects that left them inside air-conditioning. A small, dedicated team of them became my crutches.
It was a sobering reminder that I wasn’t alone in the lab. Other students needed their help too. Each of us got consumed by the pursuit of data. My project wasn’t atypical. I wasn’t especially beleaguered. This was normal for graduate school.
Years earlier, another student had also been an inadvertent messenger of this same fact. I was spending a lot of time filling air tanks and generally relaxing at a dive shop near Pasadena, California, between my trips to the hyperbaric chamber on Catalina Island. One day at the shop, a PhD student from Caltech had wandered in, looking for help. He wanted water samples from near the underwater bases of the famous tufa towers in Mono Lake in Northern California, and he had concluded that the only way to get them was to jump in. He came to the shop pleading for a dive buddy, asking for someone to accompany him down into the depths of the salty lake where periodic jets of less-dense freshwater would randomly mess with a diver’s buoyancy, down near the source of the jets where the water had such a chemically basic pH level that he expected it to burn. We had all declined.
A few days later he came back to return his rental gear. He had gone by himself, breaking the cardinal diving-safety rule of “never dive alone” because he decided he needed the data more than he needed safety. Painful-looking chemical burns formed extensive leopard spots over his face, neck, arms, and hands. But he had gotten his samples. He was happy.
Each time I walked down the now-trampled slope into the pond, I thought of that student. My friends and I had been baffled by his choice at that time, but now I understood him, even though I had long forgotten his name. My DoD-funded scholarship program required that I graduate in five years flat, even though the biomedical engineering PhD program average was roughly six years, and I was unaware of any student who had ever graduated from my lab in less than seven. The scholarship had granted me a few months’ extra grace period, but if I couldn’t get these gauges to work properly, and soon, I would be expelled from the scholarship program and forced to repay my tuition and salary from the past five years.*
I didn’t need my theory to be correct. I could publish the negative results—an “I had a theory, but here’s how I proved myself wrong” paper—and still graduate. But I needed to get the test setup working, to get some valid data, before I could solidly declare that I was wrong and write it up as a dissertation. I still thought the theory was plausible, but much more than I wanted to be right, I wanted to be finished, to have a final answer. I understood why the Caltech student, eager to finish his work, jumped without hesitation into what was basically a pond full of mildly harmful acid. Every day of testing, I jumped in too.
Perhaps this was a small taste of the desperation that the crew of the Hunley felt. They knew how dangerous their boat was, but they were starving, and they were being bombed nightly. A worse situation than mine, definitely, but also one likely to inspire unrealistic optimism.
Sitting on the footbridge, I stared at the laptop monitor. I was under a big black sun tent, but it was mostly there to keep the electronics from overheating. A sunburned stripe on my lower back was itchy. We were almost ready to put the boat back into the water. We just needed to check the internal pressure gauges again. Maybe they would work this time.
I asked one of the undergrads to hit the bow with the rubber mallet. I heard him hit the boat, and it rang out clearly across the pond. But this time, the flat lines of the readings from the pressure gauges inside the hull did not jump in response. They stayed still. I asked him to hit it again. Again, no response.
Fatigued and cranky, I insisted we test anyway, blindly hopeful it was a fluke. Matt Udelhofen and I carried the boat into the water, and I swam out to connect the gas line to the shock-tube driver.
Again, as always, there was the tiniest, most negligible response inside the boat. Frustrated, I insisted we immediately yank the boat out. I wanted to be done dealing with these gauges. I did not know what was happening. They worked perfectly on dry land while in the lab, when measuring pressures in the air, and even when inside my small metal tub in the test tank, but here inside the boat, almost nothing. Nothing. It made no sense. I dragged the boat onto the bridge. I was determined that the gauges would at least work during the mallet test. I asked the undergrad to hit the bow again. He brought the mallet down squarely on the stern, directly on the clumsily spray-painted words “CSS Tiny.”
I stared at him for a moment, processing the realization that not everybody knew the difference between bow and stern.
Then I had my eureka moment.
I grabbed the mallet and smacked the bow hard. The pressure reading jumped. I hit the stern. Nothing. I understood my mistake, I understood why the internal gauges kept failing: The gauges could only read from one direction. They were facing the bow and wouldn’t read pressures coming from any other direction. I needed to put a different gauge inside the boat.
Dripping, still wearing my life jacket, my sun hat soaked with sweat and my neoprene boots still uncomfortably full of pond, I run-sloshed to the toolbox. I pulled out the largest screwdriver I could find, a sturdy Phillips-head beast with rust spots, and I took massive strides back to the boat. Kneeling on the bridge, I lifted the handle of the screwdriver with both hands, and I plunged it straight down like a sacrificial knife through the thick rubber gasket that sealed the top of the boat off from the water.
On the top of the boat was a small removable panel. Each morning I shoved my forearm through the panel opening to place the pressure gauges as far inside as possible. The pressure gauges were toward the bow of the boat, facing forward, so far inside that the procedure to insert them always left a ring of bruises circling my forearm. They were near the bulkhead where Dixon would have sat, and where I expected the blast to most strongly penetrate the hull.
The pressure gauges I was using inside the dry hull of the boat were the go-to gauges for our lab for measuring blasts in air. I wasn’t able to use them in the water because they were not waterproof, hence my need for the gauges from the navy to measure the pressure waves outside the boat. But these air gauges had served us well for years, reliably providing measurements for all sorts of tests, so when I designed the experiment it had seemed reasonable that they would provide reliable measurements for the pressure waves in the air inside the boat.
They were shaped like mushrooms, narrow cylinders topped with slightly wider caps. On the very bottom face of the “stalk” of the mushroom was the part that did the actual pressure sensing, a small circle of mesh. These air gauges were unidirectional, meaning only the mesh panel on the face of the cylinder could sense pressure. If this mesh panel were oriented incorrectly relative to the direction that the pressure wave was traveling, the gauge would not provide a meaningful reading. The mesh panels of the two gauges were facing forward and down, toward the spar and the charge, and they were as far toward the bow as I could place them. Before each test we had hit the bow with the mallet. They read the pressure ripple from hits to the bow. But when the student accidentally hit the boat on the stern they read almost nothing because they were being struck from the wrong direction.
I blasted the Tiny from the same position as the charge of the Hunley: mostly in front of and slightly below the boat. I had assumed, because the charge was off the bow, that much of the pressure would naturally transmit through the bow. The pressures from the charges had been transmitting all along, but I had missed it, because they weren’t transmitting in through the bow. They were coming in from another direction.
Luckily, I already had a solution. The underwater gauges that I was using in the water, the gauges that had been loaned to me by the other navy engineers . . . these gauges were omnidirectional. Meaning, they measured waves coming from any direction. And even though they were mostly used underwater, they also worked in air. I had confirmed it in the lab dozens of times, when I was testing every configuration I could think of to try to replicate their alleged “failures” out at Pitt Pond.
I slid one of the omnidirectional US Navy gauges into the screwdriver hole I had just mercilessly stabbed in my submarine. I sealed it heavily with waterproof tape. The undergrad hit the boat in both the bow and the stern. It jumped both times. We put the boat back into the water.
The gauge worked like magic. With each test, it showed an internal increase in pressure precisely with the arrival of the shock wave. The initial increase was followed by exactly what I expected: a jagged, erratic waveform of pressure, the initial wave bouncing around inside the small enclosed hull. These waves were small because my shock tube was making small shocks in the water, but their shape was lethal. We knew now that they were getting in, just not through the bow. The next step was to figure out how. And how we had missed it.
Our team began testing furiously, running through every experimental variation we could think of. Each time the driver popped, almost immediately we had it open again, replacing the membrane for another trial. I was running in and out of the pond, trampling ornamental pond grasses with abandon. The excitement of sharing the data and staring at the screen together was palpable.
We changed the orientation of the boat; we changed the orientation of the driver; and we came up with test after test to characterize how the blast was propagating, through which parts of the hull, and by how much. The ultimate goal was to return to testing the boat exactly as the Hunley had been blasted, but by methodically changing the setup, we first came up with a full characterization of exactly which parts of the submarine conducted the blast and how well. We knew now that it was going in through her belly, not her bow. No more assumptions.
Inside an enclosed area, the waves bounce. They add to one another. It’s a phenomenon called constructive interference. When two positive waves intersect, they combine to form a higher pressure. It can happen with acoustic waves, with ocean waves, and with blast waves. It’s why the people hit by explosions inside of buses were killed far more often than the people in open spaces. The constructive interference amplified the pressures inside, increasing their lethality. My original gauges were only reading the initial blip that made it through the bow. I had thought that this would be most of the signal, but I was wrong. Most of the signal came in through the bottom, and then built on itself as it reflected around the interior of the sub.
By the time the sun started to set we had racked up not just the solution to my months of frustration but a tidy handful of invaluable data points. As the light faded and the mosquitoes began to descend, we packed our gear and heaved it with exhausted muscles into the back of my borrowed truck.
I tried to take the undergrads out for milk shakes. It was the only thing I could think of in that moment to say thank you. But tired, sweaty, and utterly depleted from the day, they asked if we could go another time. They wanted to go to bed. I did too. And for the first time in months, I actually slept through the night.
The Hunley held her spar on a downward angle. Using historical records, researchers have independently concluded that the depth of the torpedo on the spar could most likely be adjusted, raised or lowered, by pulling on a line attached to a spool on top of the boat. The spar was attached to the recovered boat on a hinge, consistent with the idea. She wanted to get her torpedo as far underneath the bottom of the Housatonic as possible, to follow the advice of Gabriel Rains about destroying ships. Contemporary accounts and drawings state that the torpedo was positioned 8 feet below the surface of the water, and therefore a minimum of at least 4 feet below the keel of the Hunley.
The Tiny transmitted the blast most effectively when the waves were aimed at the central part of her cylindrical body. In our tests to gauge transmission, almost nothing transmitted directly in through the bow; it is likely that the bulkhead and the water in the bilge absorbed most of the pressure waves from that direction. If the torpedo had been on a spar that was horizontally level with the submarine, more like the spar assumed to have been used by the wooden boat David that had attacked while on the surface, much smaller fractions of the lethal waves would have been able to transmit inside.
By lowering her spar, the Hunley placed herself above the level of the torpedo. By the time the propagating waves reached her underbelly, most would be traveling horizontally, but they would still have a strong vertical component. And that vertical component was ideally positioned to transmit straight through her hull. The crew may have survived if the spar had been fully horizontal, on the surface of the water, but that would likely not have destroyed the Housatonic. The Hunley was inadvertently designed to kill her own crew.