Thirty

Sea level—perpetual flux. There is a micromillimetre on the surface of the ocean that moves between sea and sky and is simultaneously both and neither. Every known life-form exists in relation to this layer. Above it, the world of land, air, sunlight, and lungs. Below it, the world of water, depth, and pressure. The deeper you go, the darker, the more hostile, the less familiar, the less measured, the less known.

A splash in the South Pacific, last June, marked a historic breach of that world. A crane lowered a small white submersible off the back of a ship and plonked it in the water. For a moment, it bobbed quietly on the surface, its buoyancy calibrated to the weight of the pilot, its only occupant. Then he flipped a switch, and the submarine emitted a frantic, high-pitched whirr. Electric pumps sucked seawater into an empty chamber, weighing the vessel down. The surface frothed as the water poured in—then silence, as the top of the submersible dipped below the waterline, and the ocean absorbed it.

Most submarines go down several hundred metres, then across; this one was designed to sink like a stone. It was the shape of a bulging briefcase, with a protruding bulb at the bottom. This was the pressure hull—a titanium sphere, five feet in diameter, which was sealed off from the rest of the submersible and housed the pilot and all his controls. Under the passenger seat was a tuna-fish sandwich, the pilot's lunch. He gazed out of one of the viewports, into the blue. It would take nearly four hours to reach the bottom.

Sunlight cuts through the first thousand feet of water. This is the epipelagic zone, the layer of plankton, kelp, and reefs. It contains the entire ecosystem of marine plants, as well as the mammals and the fish that eat them. An Egyptian diver once descended to the limits of this layer. The feat required a lifetime of training, four years of planning, a team of support divers, an array of specialized air tanks, and a tedious, thirteen-hour ascent, with constant decompression stops, so that his blood would not be poisoned and his lungs would not explode.

The submersible dropped at a rate of about two and a half feet per second. Twenty minutes into the dive, the pilot reached the midnight zone, where dark waters turn black. The only light is the dim glow of bioluminescence—from electric jellies, camouflaged shrimp, and toothy predators with natural lanterns to attract unwitting prey. Some fish in these depths have no eyes—what use are they? There is little to eat. Conditions in the midnight zone favor fish with slow metabolic rates, weak muscles, and slimy, gelatinous bodies.

An hour into the descent, the pilot reached ten thousand feet—the beginning of the abyssal zone. The temperature is always a few degrees above freezing, and is unaffected by the weather at the surface. Animals feed on "marine snow": scraps of dead fish and plants from the upper layers, falling gently through the water column. The abyssal zone, which extends to twenty thousand feet, encompasses ninety-seven per cent of the ocean floor.

After two hours in free fall, the pilot entered the hadal zone, named for the Greek god of the underworld. It is made up of trenches—geological scars at the edges of the earth's tectonic plates—and although it composes only a tiny fraction of the ocean floor, it accounts for nearly fifty per cent of the depth.

Past twenty-seven thousand feet, the pilot had gone beyond the theoretical limit for any kind of fish. (Their cells collapse at greater depths.) After thirty-five thousand feet, he began releasing a series of weights, to slow his descent. Nearly seven miles of water was pressing on the titanium sphere. If there were any imperfections, it could instantly implode.

The submarine touched the silty bottom, and the pilot, a fifty-three-year-old Texan named Victor Vescovo, became the first living creature with blood and bones to reach the deepest point in the Tonga Trench. He was piloting the only submersible that can bring a human to that depth: his own.

For the next hour, he explored the featureless beige sediment, and tried to find and collect a rock sample. Then the lights flickered, and an alarm went off. Vescovo checked his systems—there was a catastrophic failure in battery one. Water had seeped into the electronics, bringing about a less welcome superlative: the deepest-ever artificial explosion was taking place a few feet from his head.

If there were oxygen at that depth, there could have been a raging fire. Instead, a battery junction box melted, burning a hole through its external shell without ever showing a flame. Any instinct to panic was suppressed by the impossibility of rescue. Vescovo would have to come up on his own.

Seven miles overhead, a white ship bobbed in Polynesian waters. It had been built by the U.S. Navy to hunt Soviet military submarines, and recently repurposed to transport and launch Vescovo's private one. There were a couple of dozen crew members on board, all of whom were hired by Vescovo. He was midway through an attempt to become the first person to reach the deepest point in each ocean, an expedition he called the Five Deeps. He had made a fortune in private equity, but he could not buy success in this—a richer man had tried and failed. When the idea first crossed his mind, there was no vehicle to rent, not even from a government. No scientist or military had the capacity to go within two miles of the depths he sought to visit. Geologists weren't even sure where he should dive.

Vescovo's crew was an unlikely assemblage—"a proper band of thieves," as the expedition's chief scientist put it—with backgrounds in logistics, engineering, academia, and petty crime. Some on board had spent decades at sea; others were landlubbers. For more than a year, they faced challenges as timeless as bad weather and as novel as the equipment they had invented for the job. They discovered undersea mountain ranges, collected thousands of biological samples that revealed scores of new species, and burned through tens of thousands of gallons of fuel and alcohol.

In 1969, when Vescovo was three years old, he climbed into the front seat of his mother's car, which was parked on a hill outside their house. He was small and blond, the precocious, blue-eyed grandson of Italian immigrants who had come to the United States in the late nineteenth century and made a life selling gelato in the South. Vescovo put the car in neutral. It rolled backward into a tree, and he spent the next six weeks in an intensive-care unit. There were lasting effects: nerve damage to his right hand, an interest in piloting complex vehicles, and the "torturous compulsion," he said, to experience everything he could before he died.

He grew up reading science fiction, and aspired to be an astronaut; he had the grades but not the eyesight. As an undergraduate, at Stanford, he learned to fly planes. Afterward, he went to M.I.T., for a master's degree in defense-and-arms-control studies, where he modelled decision-making and risk—interests that later converged in overlapping careers as a Reserve Naval Intelligence officer and a businessman. Vescovo was deployed as a targeting officer for the NATO bombing of Kosovo, and, as a counterterrorism officer, he was involved in a hostage rescue in the Philippines. He learned Arabic and became rich through finance and consulting jobs, and, later, through a private-equity firm, Insight Equity, in the suburbs of Dallas, where he lives.

Vescovo started going on increasingly elaborate mountaineering expeditions, and by 2014 he had skied the last hundred kilometres to the North and South Poles and summited the highest peak on every continent. He had narrowly survived a rock slide near the top of Mt. Aconcagua, in the Argentinean Andes, and had come to embrace a philosophy that centered on calculated risk. Control what you can; be aware of what you cannot. Death, at some point, is a given—"You have to accept it," he said—and he reasoned that the gravest risk a person could take was to waste time on earth, to reach the end without having maximally lived. "This is the only way to fight against mortality," he said. "My social life was pretty nonexistent, but it just wasn't a priority. Life was too interesting." He grew his hair down to his shoulders, and touched up the color, even as his beard turned white. On weekends, he used his private jet to shuttle rescue dogs to prospective owners all over the U.S. At sea, according to members of his expedition team, he spent hours in his cabin alone, playing Call of Duty and eating microwaved macaroni and cheese.

But every age of exploration runs its course. "When Shackleton sailed for the Antarctic in 1914, he could still be a hero. When he returned in 1917 he could not," Fergus Fleming writes, in his introduction to "South," Ernest Shackleton's diary. "The concept of heroism evaporated in the trenches of the First World War." While Shackleton was missing in Antarctica, a member of his expedition cabled for help. Winston Churchill responded, "When all the sick and wounded have been tended, when all their impoverished & broken hearted homes have been restored, when every hospital is gorged with money, & every charitable subscription is closed, then & not till then wd. I concern myself with these penguins."

A century later, adventurers tend to accumulate ever more meaningless firsts: a Snapchat from the top of Mt. Everest; in Antarctica, the fastest mile ever travelled on a pogo stick. But to open the oceans for exploration without limit—here was a meaningful record, Vescovo thought, perhaps the last on earth. In 1961, John F. Kennedy said that "knowledge of the oceans is more than a matter of curiosity. Our very survival may hinge upon it." Yet, in the following decades, the hadal trench nearest to the U.S. became a dumping ground for pharmaceutical waste.

In September, 2014, Vescovo sent an inquiry to Triton Submarines, a small manufacturer in Vero Beach, Florida. He noted that he was a jet and helicopter pilot familiar with the "procedure-driven piloting of complex craft," and outlined what became the Five Deeps Expedition.

Patrick Lahey, the president of Triton, took up scuba diving when he was thirteen years old, and discovered that he felt more at home underwater than he did on land. The muted silence, the slow, deep breaths—diving forced him into a kind of meditative state. "I love the feeling of weightlessness," he told me. "I love moving around in three dimensions, instead of two." Lahey attended commercial diving school, to learn underwater welding and construction for dams, bridges, and oil-and-gas installations. "Just about anything you might do out of the water you could do underwater," he said. "You bolt things, you cut things, you weld things together, you move things, you recover things." Water conducts electricity, and sometimes, he added, "you can feel it fizzing in your teeth."

In 1983, when he was twenty-one, he carried out his first submarine dive, to fourteen hundred feet, to inspect an oil rig off the coast of Northern California. He was profoundly affected by the experience—to go deep one hour and surface the next, with "none of the punitive decompression," he said. By the time Vescovo contacted him, Lahey had piloted more than sixty submersibles on several thousand dives. An expedition leader who has worked with him for decades told me that he is, "without question, the best submarine pilot in the world."

Lahey co-founded Triton in 2007. The business model was to build private submersibles for billionaires, including a Russian oligarch and a member of a Middle Eastern royal family. (In the years leading up to the first order, Lahey used to be laughed at when he attended boat shows; now there are companies that build support vessels for yachts, to carry helicopters, submarines, and other expensive toys.) But his deeper aspiration was to make other people comprehend, as Herman Melville wrote, in "Moby-Dick," that in rivers and oceans we see "the image of the ungraspable phantom of life; and this is the key to it all." After a few dives, many of Lahey's clients started allowing their vehicles to be used for science and filming.

Vescovo didn't care if Lahey sent him to the bottom of the ocean in a windowless steel ball; he just wanted to get there. But Lahey declined to build anything that didn't have a passenger seat, for a scientist; a manipulator arm, for collecting samples; and viewports, so that the occupants could appreciate the sensation of submergence. Such features would complicate the build, possibly to the point of failure. But Lahey has a tendency to promise the reality he wants before he's sure how to deliver it. "It wasn't really a business decision," a Triton engineer told me. "He wanted to build this. Giving up was not an option." Lahey saw Vescovo's mission as a way to develop and test the world's first unlimited hadal exploration system—one that could then be replicated and improved, for scientists.

Vescovo flew to the Bahamas, and Lahey took him for a test dive in Triton's flagship submersible, which has three seats and is rated to a depth of thirty-three hundred feet. The third seat was occupied by an eccentric British man in his thirties, named John Ramsay, who didn't seem to enjoy the dive; he was preoccupied with what he didn't like about the submersible—which he had designed.

"I never really had a particular passion for submarines," Ramsay, who is Triton's chief submarine designer, told me. "I still don't, really." What he does love is that he gets to design every aspect of each machine, from the central frame to the elegant handle on the back of the hatch. Car manufacturers have entire teams design a seat or a fender, and then produce it at scale. But nearly every Triton submarine is unique; Ramsay determines how he wants things to be, and a dozen or so men in Florida start building.

Ramsay, who works out of a spare bedroom in the wilds of southwest England, has never read a book about submarines. "You would just end up totally tainted in the way you think," he said. "I just work out what it's got to do, and then come up with a solution to it." The success or the failure of Vescovo's mission would rest largely in his hands.

"If Victor dies, and it's your fault, you’ve got to kill yourself," he told his wife, Caroline.

"Would you, though?" she replied.

"Of course!"

A submariner thinks of space and materials in terms of pressure, buoyancy, and weight. Air rises, batteries sink; in order to achieve neutral buoyancy—the ability to remain suspended underwater, without rising or falling—each component must be offset against the others. The same is true of fish, which regulate their buoyancy through the inflation and deflation of swim bladders.

Ramsay's submarines typically center on a thick acrylic sphere, essentially a bubble; release it underwater and it will pop right up to the surface. But acrylic was not strong enough for Vescovo's submersible. At the bottom of the deepest trench, every square inch would have to hold back sixteen thousand pounds of water—an elephant standing on a stiletto heel.

Ramsay settled on titanium: malleable and resistant to corrosion, with a high ratio of strength to density. The pressure hull would weigh nearly eight thousand pounds. It would have to be counterbalanced by syntactic foam, a buoyant filler comprising millions of hollow glass spheres. For the submarine to stay upright, the foam would have to go above the hull, providing upward lift—like a hot-air balloon, for water. "As long as the heavy stuff hangs in balance below the buoyant stuff, the sub will always stay upright," Ramsay explained.

The hull required the forging of two slabs of titanium into perfect hemispheres. Only one facility in the world had a chamber that was sufficiently large and powerful to subject the hull to pressures equivalent to those found at full ocean depth: the Krylov State Research Center, in St. Petersburg, Russia. Lahey attended the pressure test. There was no backup hull; an implosion would end the project. "But it worked—it validated what we were doing," Lahey told me.

Nearly every Triton submarine is unique. For the Limiting Factor, John Ramsay, its principal designer, said, "You’re solving problems that have never existed before, with parts that have never existed before."

The submarine is fitted with acoustic tracking and communications equipment, so that Vescovo can talk to the ship and the ship can triangulate his position in the water.

Trunk pumps churn water into the empty chamber above the hatch. As water replaces air, the submarine descends to the ocean floor.

Thrusters allow Vescovo to move in any direction as he explores the ocean floor. In designing the submarine, Ramsay took inspiration from rugby balls and bullet trains, which are the only two objects he could think of that have two axes of symmetry and can go equally fast in both directions.

To leave the bottom, Vescovo drops a five-hundred-and-fifty-pound weight to the ocean floor. Hours later, as the submarine bobs at the surface, one-way valves allow water to pour out of the trunk, creating enough buoyancy for the pilot to exit the sub.

It was the middle of summer, 2018, in South Florida, and Triton's technicians were working fifteen hours a day, in a space with no air-conditioning. Lahey paced the workshop, sweating, trying to encourage his team. The men who were building the world's most advanced deep-diving submersible had not attended Stanford or M.I.T.; they were former car mechanics, scuba instructors, and underwater welders, hired for their work ethic and their practical experience. The shop foreman used to be a truck driver. The hydraulics expert had a bullet in his abdomen, from his days running cocaine out of Fort Lauderdale, in the eighties. One of the electricians honed his craft by stealing car radios, as a teen-ager. ("I was really good at it," he told me.) Lahey, for his part, said that he was named—and later exonerated—by the federal government as an unindicted co-conspirator in a narcotics-trafficking operation involving a Soviet military submarine and a Colombian cartel.

Every major component of Vescovo's submarine had to be developed from scratch. The oil-and-gas industry had established a supply chain of components that are pressure-rated to around six thousand metres—but that was only half the required depth. Before assembling the submarine, the Triton team spent months imploding parts in a pressure chamber, and sending feedback to the manufacturers. "You’re solving problems that have never existed before, with parts that have never existed before, from venders who don't know how to make them," Ramsay said.

The rest of the expedition team was on a ship docked in the harbor at Vero Beach, waiting. Vescovo remained at home in Dallas, training on a simulator that Triton had rigged up in his garage. On Lahey's recommendation, he had hired Rob McCallum, an expedition leader and a co-founder of EYOS Expeditions, to inject realism into a project that might otherwise die a dream.

For every Vescovo who goes to the South Pole, there is a McCallum making sure he stays alive. (McCallum has been to Antarctica a hundred and twenty-eight times.) "I love it when clients come through the door and say, ‘I’ve been told this is impossible, but what do you think?’ " he said to me. "Well, I think you’ve just given away your negotiating position. Let's have a glass of wine and talk about it."

McCallum—who is trim but barrel-chested, with a soft voice and a Kiwi accent—grew up in the tropics of Papua New Guinea, and became a polar guide. He is a trained medic, dive master, firefighter, aircraft pilot, and boat operator, a former New Zealand park ranger who has served as an adviser to the Norwegian Navy. He speaks three Neo-Melanesian languages, and can pilot a Zodiac boat standing up, in sixteen-foot waves. He is the subject of a "Modern Love" column, in the Times. ("My father warned me about guys like you," the author recalls telling him, before marrying him anyway.) McCallum and his associates have discovered several high-profile shipwrecks, including Australian and American warships and an Israeli military submarine. A few months ago, he showed me on his computer an object on a sonar scan, which he believes to be Amelia Earhart's plane.

Vescovo asked what McCallum required from him. "The first thing I need is for you to triple the budget," he replied. He also shot down several of Vescovo's proposals, from the antiquated (no alcohol or spouses on board) to the insane (installing fake military hardware on the bow; bringing his dog to the deepest point on earth).

Five oceans, five deeps—a journey around the world and to both poles. McCallum explained that the expedition would have to be anchored by the polar dives. The likely dive spot in the Arctic Ocean is covered by ice for much of the year, but there is a two-week dive window, beginning in late August. The Antarctic, or Southern Ocean, dive could be done in February, the height of summer in that hemisphere. The team would have to avoid hurricane season in the Atlantic, and monsoon season in the Pacific, and otherwise remain flexible, for when things inevitably went wrong.

Lahey persuaded Vescovo to buy the U.S.N.S. Indomitable, a two-hundred-and-twenty-foot vessel that he had found at a drydock in Seattle. It was built as an intelligence-gathering ship, in 1985, and spent much of the next fifteen years prowling the world's oceans, towing an undersea listening device. "It was owned by the Navy but operated by civilians," McCallum told me. He winked. "I didn't say C.I.A.—I just said civilians." Vescovo renamed it the Pressure Drop, for a spaceship from the "Culture" series of science-fiction novels, by Iain M. Banks.

The Arctic-dive window was fast approaching, and it seemed unlikely that the submersible would be ready. "That's when Patrick Lahey's overflowing optimism went from being an incredible, endearing personality trait to being a huge issue," Stuart Buckle, the Pressure Drop's captain, said. "Every day, Patrick would say, ‘Oh, yes, it’ll be ready in one or two days.’ And then two days pass, and he’d say, ‘It’ll be ready in two days.’ "

The final step in building a submarine is to put it in a swimming pool or in the water at a marina. "You need to know how much it weighs and how much it displaces," Ramsay said, because the average density of the craft and its passengers must be equal to that of the water in which it is submerged. "You’ve only calculated the volume of each object through computer models, which can't possibly represent the actual thing, with all its tolerances. Things are a bit bigger, things are a bit smaller, cables are fatter."

But there was no time to do this before loading it onto the ship and setting off for sea trials, in the Bahamas. They left Florida without knowing how much the submarine displaced. "It had never even touched the water," Ramsay said. "It was just ‘Right, off we go. Let's see if it works.’ "

"When people talk about sea trials, they always think about testing a ship or testing a sub," McCallum told me. "But, really, what you’re doing is you’re testing people. You are testing systems, processes, conditions, and teams."

Buckle, the captain, dropped anchor near Great Abaco Island, in the Bahamas, and immediately became alarmed by the Triton crew's cavalier approach to safety. He had grown up in the Scottish Highlands, and gone to sea when he was seventeen years old. "Me and my guys were trying to adjust from the oil-and-gas industry, where you need a signed bit of paper to do anything, and to go out on deck you have to have your overalls, hard hats, goggles, earmuffs, and gloves," Buckle said. "Whereas a lot of the Triton guys were used to walking around in shorts and flip-flops, like you watch on ‘American Chopper.’ They were grinding and drilling and using hydraulic awls, looking at it, sparks flying everywhere, not wearing safety glasses or anything. To them, if something catches fire, it's funny—it's not an issue."

Vescovo named the submarine the Limiting Factor, for another spaceship from the "Culture" series. It was secured to a custom-built cradle, which could be rolled backward on metal tracks, to lower the sub into the ocean from the aft deck of the ship. During launch operations, the Triton crew attached it to a hook that hung down from a crane, known as an A-frame, shaped like an enormous hydraulic swing set. Buckle had asked Vescovo to buy a larger A-frame—one that was "man-rated" by a certification agency, so that they could launch the submersible, which weighs around twenty-six thousand pounds, with the pilot inside and the hatch secured. But there was no time to install one. So the Triton crew lowered the empty submersible into the water, and the ship's crew, using a different crane, launched a Zodiac boat over the starboard side. McCallum climbed into the Zodiac, and drove the pilot to the sub as it was being towed behind the ship.

The ship had no means of tracking the submarine underwater. "Once he left the surface, I had no idea where he was," Buckle said. "All we had at that point was one range." Buckle could see, for example, that the Limiting Factor was five hundred metres away, but he didn't know in which direction. "As long as that number was getting bigger, that meant he wasn't surfacing directly under me," he said. "If it just kept getting smaller and smaller, I’m in trouble."

"The thing about driving a ship is that unless you know how to drive a ship you never see the bad stuff," McCallum told me. "It's only when the captain's going ‘Christ, that was close!’ that you go ‘Really? Was it?’ "

Other incidents were unambiguous. "I was seeing Triton guys bouncing up the ladders without holding the handrails, wanting to jump on top of things while they were still swinging from the crane," Buckle recalled. Ropes failed, deck equipment snapped under stress. "One of the big ratchet hooks blew off the top of the hangar, and missed Patrick's head by that much," McCallum said, holding his fingers a couple of inches apart. "Just missed him. And he wasn't wearing a helmet, so that would have killed him."

Lahey piloted the sub on its earliest dives—first to twenty metres, then fifty, then a thousand. Electronic systems failed. The hatch leaked. Emergency lights malfunctioned, and drop weights got stuck. Pre-dive checklists labelled several switches "inoperable." Post-dive checklists noted critical components lost and fallen to the seafloor.

"In a sea trial, you’re trying to break stuff—you’re trying to work out where your weakest link is," McCallum said. "It's incredibly demoralizing. You never feel as if you’re making any meaningful forward progress." Each morning, he delivered a pre-dive briefing to members of the ship and submarine crews. "Don't be disheartened by the long list of things that broke," he told them. "Rejoice, because those are things that are not going to fail in the Southern Ocean—and if they did fail in the Southern Ocean we’d be fucked."

On September 9, 2018, Patrick Lahey piloted the Limiting Factor to the bottom of the Abaco Canyon, more than three miles down. It was the ninth time that the submersible had been in the water. Everything worked. The next day, Lahey repeated the dive, with Vescovo as the lead pilot. When they reached the bottom, Vescovo turned on the control unit that directs the manipulator arm. Something wasn't right. He and Lahey glanced at each other. "Do you smell that?" Lahey asked.

"Yes."

There was a puff of smoke in the capsule. Vescovo and Lahey grabbed the "spare air"—scuba regulators, with two-minute compressed-air cannisters—so that they wouldn't pass out while preparing the emergency breathing apparatus. A circuit breaker tripped, automatically switching off the control unit for the manipulator arm, and the acrid smell dissipated. Lahey, who was training Vescovo to handle crises underwater, asked what they should do.

"Abort the dive?" Vescovo said.

"Yes." They were two hours from the surface.

Ramsay and Tom Blades, Triton's chief electrical designer, had devised numerous safety mechanisms. Most systems were duplicated, and ran on separate electrical circuits, in case one of the batteries failed. The thrusters could be ejected if they became entangled; so could the batteries, to drop weight and provide buoyancy. The five-hundred-and-fifty-pound surfacing weight was attached by an electromagnet, so that if the sub lost electricity it would immediately begin its ascent. There was also a dead-man switch: an alarm went off if the pilot failed to check in with the ship, and if he failed to acknowledge the alarm the weights would automatically drop.

"Whenever we had any significant failure of some kind, the only thing that mattered was why," Vescovo said. "If you can identify the problem, and fix it, what are you going to do? Give up? Come on. That didn't even cross my mind. Maybe other people get freaked out. I’ve heard of that happening. But if you’re mountain climbing and you fall, are you not going to climb again? No. You learn from it, and keep going."

By the middle of September, the sea trials had given way to "advanced sea trials"—a euphemism to cover for the fact that nothing was working. The Arctic Ocean dive window had already passed. Buckle was especially concerned about the launch-and-recovery system. The cranes were inadequate, and poorly spaced. One of the support vessels, which had been selected by Triton, was eighteen years old, and its rubber perimeter was cracking from years of neglect in the Florida sun. "I was pretty pissed off at that point," Buckle told me. "I had put my guys in a difficult situation, because they were trying to compensate for structural issues that you couldn't really work around. You can only piss with the dick you’ve been given."

McCallum redesigned the expedition schedule to begin with the Puerto Rico Trench, in the Atlantic Ocean, in December, followed by Antarctica, in early February. The adjustment added cost but bought time.

When Alan Jamieson, the expedition's chief scientist, contacted Heather Stewart, a marine geologist with the British Geological Survey, and told her that Vescovo wanted to dive to the deepest point of each ocean, she replied that there was a problem: nobody knew where those points were.

Most maps showing the ocean floor in detail are commissioned by people looking to exploit it. The oil-and-gas and deep-sea-mining industries require extensive knowledge, and they pay for it. But, with a few exceptions, the characteristics of the deepest trenches are largely unknown. As recently as the nineteen-sixties, ocean depths were often estimated by throwing explosives over the side of a ship and measuring the time it took for the boom to echo back from the bottom.

It may appear as if the trenches are mapped—you can see them on Google Earth. But these images weren't generated by scanning the bottom of the ocean; they come from satellites scanning the top. The surface of the ocean is not even—it is shaped by the features beneath it. Trenches create mild surface depressions, while underwater mountain ranges raise the surface. The result is a vaguely correct reading—here is a trench!—with a ludicrous margin of error. Every pixel is about five hundred metres wide, and what lies below may be thousands of feet deeper or shallower than the satellite projects, and miles away from where it appears on the map.

Vescovo would have to buy a multibeam echo sounder, an advanced sonar mapping system, to determine precise depths and dive locations. He chose the Kongsberg EM-124, which would be housed in a massive gondola underneath the ship. No other system could so precisely map hadal depths. Vescovo's purchase was the very first—serial number 001.

That November, Buckle sailed the Pressure Drop to Curaçao, off the coast of Venezuela, to have the EM-124 and a new starboard crane installed. But there was still no time to order a man-rated A-frame—its purchase, delivery, and installation would require that they miss the Antarctic dive window, adding a year to the expedition. "He's a wealthy dude, but he's not like Paul Allen or Ray Dalio," Buckle said of Vescovo. "He hasn't got that kind of money. This is a huge commitment of his resources."

Stewart prepared a list of possible dive locations, which earned her a spot on the expedition. For others, participation was largely a matter of luck. Shane Eigler had started working at Triton the previous year, after Kelvin Magee, the shop foreman, sent him a Facebook message asking if he’d like to build submarines. They had met in the two-thousands, after Eigler had saved up enough money by growing marijuana to pay for dive lessons. Magee was his instructor. Later, Eigler worked as a car mechanic. "Building submarines—this shit is exactly the same as cars, just different components," Eigler told me.

On December 14th, the Pressure Drop set off for the Puerto Rico Trench, from the port of San Juan. "Been feeling a little queasy ever since we got underway," Eigler wrote that night, in an e-mail to his wife. It was his first time at sea.

Vescovo and Lahey went for a test dive down to a thousand metres. It was Lahey's last chance to train Vescovo in the Limiting Factor before he would attempt an eight-thousand-metre dive, solo, to the bottom of the Puerto Rico Trench. A scientific goal for the expedition was to collect a rock sample from the bottom of each trench, so Lahey switched on the manipulator arm.

Seconds later, on the Pressure Drop, a transmission came up from below. "Control, this is L.F.," Lahey said. "We have lost the arm. It has fallen off."

It was December 17th. After surfacing, Vescovo and Lahey walked into McCallum's office, toward the stern of the ship. "Patrick was under immense pressure that would have crushed almost anybody else I know," McCallum said. "He had applied a huge amount of his team's intellectual capital to this project, at the expense of all other projects, and yet things were just not quite where they needed to be."

Vescovo called off the expedition. "I think I’m just going to write this whole thing off as bad debt," he said. The manipulator arm had cost three hundred and fifty thousand dollars, and there was no spare.

Lahey begged for more time. "Give my guys one more day," he said. Vescovo relented, and went up to his cabin. No one saw him for the next thirty-two hours. "The more time I spend with Victor, the more I think he is Vulcan in his decision-making but not in his emotions," Buckle told me. "He's one of those guys who has a veneer of calm, but then probably goes into his cabin and screams into his pillow after he's been told the fifth bit of bad news that day." (Vescovo denies screaming into his pillow.)

Lahey pulled his team into the submarine hangar. "Do you think you can fix this fucking thing?" he asked.

Blades noted that the loss of the manipulator arm had freed up an electrical junction box, creating an opportunity to fix nearly everything else that was wrong with the electronics. "Basically, Tom Blades hot-wired the sub," Lahey explained. "There was literally a jumper cable running through the pressure hull, tucked behind Victor's seat."

On December 19th, Vescovo climbed into the Limiting Factor and began his descent. "The control room was just packed, and you could cut the atmosphere with a knife the entire way down," Stewart told me. "Patrick was just in his chair, ear to the radio, just wringing sweat."

At 2:55 P.M., Victor Vescovo became the first person to reach the deepest point in the Atlantic Ocean, eight thousand three hundred and seventy-six metres. It was his first solo dive, and it was flawless.

That night, "Victor was wandering around, drinking out of a bottle of champagne," McCallum said. "It was the first time we’d seen Victor relax. It was the first time we’d seen Victor touch alcohol. And from that point we knew we were going to take this around the world."

"Puerto Rico was the starting gun," Vescovo told me. "The Southern Ocean was the forge."

Waves are local—the brushing of the ocean by the wind. Swells roll for thousands of miles across open water, unaffected by the weather of the moment.

On January 24, 2019, the Pressure Drop set off from the port of Montevideo, Uruguay, to dive the South Sandwich Trench, the deepest point of the Southern Ocean. Buckle and his crew had loaded the ship with cold-weather gear, and provisions for more than a month. There was a five-thousand-mile journey ahead of them, and the ship could barely go nine knots.

"Captain, can I have a word?" Peter Coope, the chief engineer, asked. "Is this ship going to be O.K.?"

"Yes," Buckle replied. "Do you think I would invite on board all the people I like working with most in the world, and then sail us all to a certain death?"

But Buckle wasn't so sure. A year earlier, when he’d first walked up the gangplank, he wondered why Triton had chosen this ship. The Pressure Drop hadn't been in service in several years. The hull was watertight, but there were holes in the steel superstructure, and the shipyard had stripped every functional component. The steering system had been wired in reverse; turn one way and the ship went the other. "It's a classic case of people who have spent a lot of time on boats thinking they know boats," Buckle told me. "I’ve spent a lot of time on planes, but if Victor said, ‘I want to buy a 747,’ I wouldn't go up and say, ‘Yes, that one is great—buy that one.’ I’d get a pilot or a flight engineer to do it." Buckle's first officer recalled, "The ship was fucking breaking apart."

After the purchase, Buckle and a small crew of mostly Scottish sailors spent two months living near a dock yard in Louisiana, refitting and repairing the ship. "Stu took a huge risk—not only for himself but for all his officers," McCallum told me. "He handpicked the guys, pulled them off of very well-paying oil-and-gas jobs, and got them to follow him to bumfuck nowhere." In the evenings, Buckle and his crew drank beer on the top deck, and tossed pizza slices to alligators in the bayou. The ship came with no manuals, no electrical charts. "It was just a soul-destroying, slow process," Buckle said.

Now Buckle was steering the Pressure Drop into the Southern Ocean, the site of the most reliably violent seas in the world. After a few nights, Erlend Currie, a sailor from the Orkney Islands, shoved a life jacket under the far side of his bunk, so that the mattress would form a U shape, and he wouldn't fall out.

"You get these nasty systems rolling through, with just little gaps between them," McCallum told me. McCallum has seen waves in the Southern Ocean crest above ninety feet. He had carefully mapped out a dive window, between gales, and brought on board an ice pilot and a doctor. "If something goes wrong, there's no port to go to, and there's no one to rescue you," he said.

Albatross trailed the ship for the first several days. Soon they disappeared and the crew began seeing whales and penguins. "Filled with trepidation, we steamed into the teeth of the area where, on the old maps, they used to write, ‘Here Be Monsters,’ " Vescovo told me.

On the forecastle deck, in the control room, a cheerful, brown-haired Texan named Cassie Bongiovanni sat before four large monitors, which had been bolted to the table. Bongiovanni, who is twenty-seven years old, was finishing a master's degree in ocean mapping at the University of New Hampshire when Rob McCallum called and said that he needed someone to run a multibeam sonar system for one and a half laps around the world. She graduated at sea while mapping Vescovo's dive location in the Puerto Rico Trench.

As the head sonar operator, Bongiovanni had to make perfect decisions based on imperfect information. "The sound is generated from the EM-124, housed inside the giant gondola under the ship," she said. "As it goes down, the width of each sound beam grows, so that in the deepest trenches we’re only able to pick up one point every seventy-five metres or so." In these trenches, it takes at least seven seconds for sound to reach the bottom, and another seven seconds to return. In that gap, the ship has moved forward, and has pitched and rolled atop the surface of the sea. Bongiovanni also had to account for readings of sound speed at each dive site, as it is affected by variations in temperature, salinity, and depth.

The purchase and installation of the EM-124 cost more than the ship itself, but its software was full of bugs. Each day, Bongiovanni oscillated between awe and frustration as she rebooted it, adjusted parameters, cleaned up noisy data, and sent e-mails to Kongsberg, the maker, to request software patches. The expedition wasn't merely the first to dive the South Sandwich Trench but the first to map it as well.

Buckle positioned the ship over the dive site. A Triton mechanic named Steve Chappell was assigned the role of "swimmer," meaning that he would balance atop the Limiting Factor as it was lowered into the water, and disconnect the towline before it went down. He wore a dry suit; polar waters can rapidly induce involuntary gasping and vertigo, and even talented swimmers can drown within two minutes. For a moment, he lay on a submarine bucking in the middle of the Southern Ocean, fumbling with wet ropes, fingers numb. Then a Zodiac picked him up and took him back to the Pressure Drop, where he warmed his hands by an exhaust vent. Vescovo started the pumps, and the Limiting Factor began its descent.

Dive protocols required that Vescovo check in with the surface every fifteen minutes and announce his depth and heading and the status of his life-support system. But, after forty-five hundred metres, the communications system failed. The ship could still receive Vescovo's transmissions, but Vescovo couldn't hear the replies.

Abyssal critters drifted past the viewports. It is customary to abort a dive thirty minutes after losing communications, but Vescovo knew that he might never have another chance to reach the bottom of the Southern Ocean, so he kept going. He liked the sensation of being truly alone. Sometimes, on the surface, he spoke of human nature as if it were something he had studied from the outside. Another hour passed before he reached the deepest point: seven thousand four hundred and thirty-three metres. The point had never been measured or named. He decided to call it the Factorian Deep.

That night, Alan Jamieson, the chief scientist, stood on the aft deck, waiting for biological samples to reach the surface. "Most marine science is gritty as fuck," he told me. "It's not just ‘Look at the beautiful animal,’ or ‘Look at the mysteries of the deep.’ It's all the weird vessels we end up on, the work of hauling things in and out of the water." Jamieson, a gruff, forty-two-year-old marine biologist, who grew up in the Scottish Lowlands, is a pioneer in the construction and use of hadal landers—large, unmanned contraptions with baited traps and cameras, dropped over the side of a ship. In the past two decades, he has carried out hundreds of lander deployments in the world's deep spots, and found evidence of fish and critters where none were thought to be. Now, as snow blew sideways in the darkness and the wind, he threw a grappling hook over the South Sandwich Trench and caught a lander thrashing in the waves.

There were five landers on board. Three were equipped with advanced tracking and communications gear, to lend navigational support to the sub underwater. The two others were Jamieson's—built with an aluminum frame, disposable weights, and a sapphire window for the camera, to withstand the pressure at depth. Before each dive, he tied a dead mackerel to a metal bar in front of the camera, to draw in hungry hadal fauna. Now, as he studied the footage, he discovered four new species of fish. Amphipods scuttled across the featureless sediment on the seafloor, and devoured the mackerel down to its bones. They are ancient, insect-like scavengers, whose bodies accommodate the water—floating organs in a waxy exoskeleton. Their cells have adapted to cope with high pressure, and "they’ve got this ridiculously stretchy gut, so they can eat about three times their body size," Jamieson explained. Marine biologists classify creatures in the hadal zone as "extremophiles."

The following night, one of Jamieson's landers was lost. "Usually, things come back up where you put them, but it just didn't," Buckle said. "We worked out what the drift was, and we then sailed in that drift direction for another three or four hours, with all my guys on the bridge—searchlights, binoculars, everyone looking for it. And we just never found it."

The second one surfaced later that night. But during the recovery it was sucked under the pitching ship and went straight through the propeller. By now, there was a blizzard, and the ship was heaving in eighteen-foot waves. "I lost everything—just fucking everything—in one night," Jamieson said. Vescovo suggested naming the site of the lost landers the Bitter Deep.

The Pressure Drop set off east, past a thirty-mile-long iceberg, for Cape Town, South Africa, to stop for fuel and food. Bongiovanni left the sonar running, collecting data that would correct the depths and the locations of key geological features, whose prior measurements by satellites were off by as much as several miles. (Vescovo is making all of the ship's data available to Seabed2030, a collaborative project to map the world's oceans in the next ten years.) Meanwhile, Jamieson cobbled together a new lander out of aluminum scraps, spare electronics, and some ropes and buoys, and taught Erlend Currie, the sailor from the Orkney Islands, to bait it and set the release timer. Jamieson named the lander the Erlander, then he disembarked and set off for England, to spend time with his wife and children. It would take several weeks for the ship to reach its next port stop, in Perth, where the Triton crew would install a new manipulator arm.

At the time, the deepest point in the Indian Ocean was unknown. Most scientists believed that it was in the Java Trench, near Indonesia. But nobody had ever mapped the northern part of the Diamantina Fracture Zone, off the coast of Australia, and readings from satellites placed it within Java's margin of error.

The Pressure Drop spent three days over the Diamantina; Bongiovanni confirmed that it was, in fact, shallower than Java, and Currie dropped the Erlander as Jamieson had instructed. When it surfaced, around ten hours later—the trap filled with amphipods, including several new species—Currie became the first person to collect a biological sample from the Diamantina Fracture Zone.

The Java Trench lies in international waters, which begin twelve nautical miles from land. But the expedition's prospective dive sites fell within Indonesia's Exclusive Economic Zone; according to U.N. conventions, a country has special rights to the exploration and exploitation of marine resources, as far as two hundred nautical miles from the coast. McCallum had spent much of the previous year applying for permits and permissions; he dealt with fifty-seven government agencies, from more than a dozen countries, in order to plan the Five Deeps.

For several months, the Indonesian government ignored McCallum's inquiries. Then he was bounced among ten or more agencies, to which he sent briefing materials about the submersible, the ship, the crew, and the mission. Between the Atlantic and the Antarctic dives, Vescovo flew to Jakarta to deliver a lecture, and he offered to bring an Indonesian scientist to the bottom of the trench. But when the ship arrived in Bali McCallum still hadn't received permission to dive.

Officially, this meant that the team could not carry out any scientific work in the Java Trench. But the international law of the sea allows for the testing of equipment, and, after Java, the next set of dives, in the Pacific Ocean, would be the deepest of all. "So we tested the sub a few times," McCallum said, smiling. "We tested the landers, we tested the sonar—we tested everything."

The Java Trench is more than two thousand miles long, and the site of violent seismic activity. Surveys in the northern part show evidence of landslides, from the 2004 earthquake that triggered a tsunami with hundred-foot waves that killed a quarter of a million people across Southeast Asia. Farther south, satellites had detected two deep pools, several hundred miles apart. The Pressure Drop mapped both sites, and Bongiovanni discovered that, in fact, the deepest point was between them, in a small pool that had previously gone unnoticed. It may be a new rupture in the ocean floor.

Buckle positioned the Pressure Drop over the pool, and turned off the ship's tracking and communications equipment. McCallum hoisted a pirate flag. The climate was tropical, eighty-six degrees, the ocean calm, with slow, rolling swells and hardly a ripple on the surface. On the morning of April 5, 2019, the Triton crew launched the Limiting Factor without incident, and Vescovo dived to the deepest point in the Java Trench.

Mountaineers stand atop craggy peaks and look out on the world. Vescovo descended into blackness, and saw mostly sediment at the bottom. The lights on the Limiting Factor illuminated only a few feet forward; the acrylic viewports are convex and eight inches thick. Whatever the true topography of the rock underneath, hadal trenches appear soft and flat at the deep spots. Flip a mountain upside down and, with time, the inverted summit will be unreachable; for as long as there has been an ocean, the trenches have been the end points of falling particulate—volcanic dust, sand, pebbles, meteorites, and "the billions upon billions of tiny shells and skeletons, the limy or silicious remains of all the minute creatures that once lived in the upper waters," Rachel Carson wrote, in "The Sea Around Us," in 1951. "The sediments are a sort of epic poem of the earth."

Vescovo spent three hours at the bottom, and saw a plastic bag through the viewports. In the Puerto Rico Trench, one of the Limiting Factor's cameras had captured an image of a soda can. Scientists estimate that in thirty years the oceans will hold a greater mass of plastic than of fish. Almost every biological sample that Jamieson has dredged up from the hadal zone and tested in a lab has been contaminated with microplastics. "Does it harm the ability of these animals to feed, to maneuver, to reproduce?" McCallum said. "We don't know, because we can't compare one that's full of microplastics with one that's not. Because there aren't any."

The walls of trenches are filled with life, but they were not Vescovo's mission. "It's a little bit like going to the Louvre, putting your running shoes on, and sprinting through it," Lahey said. "What you really want to do is to go there with someone who can tell you what you’re looking at." The next day, Vescovo told Lahey that he could take Jamieson to the bottom of the trench. "I don't want to go to the deepest point, because that's boring," Jamieson said. "Let's go somewhere really cool."

Four and a half miles below the ship, the Australia tectonic plate was being slowly and violently subsumed by the Eurasia plate. Bongiovanni had noticed a staircase feature coming out of a fault line, the result of pressure and breakage on a geological scale. It extended more than eight hundred feet up, beyond vertical, with an overhang—an outrageously difficult dive. Lahey would have to back up as they ascended, with no clear view of what was above the sub.

The hatch started leaking during the descent, but Lahey told Jamieson to ignore it—it would seal with pressure. It kept dripping for more than ninety minutes, and stopped only at fifteen thousand feet. "I fucking told you it would seal," Lahey said.

The Limiting Factor arrived at the bottom just after noon. Lahey approached the fault-line wall, and headed toward some bulging black masses. From a distance, they looked to Jamieson like volcanic rock, but as Lahey drew closer more colors came into view—brilliant reds, oranges, yellows, and blues, cloaked in hadal darkness. Without the lights of the submarine, the colors might never have been seen, not even by creatures living among them. These were bacterial mats, deriving their energy from chemicals emanating from the planet's crust instead of from sunlight. It was through this process of chemosynthesis that, billions of years ago, when the earth was "one giant, fucked-up, steaming geological mass, being bombarded with meteorites," as Jamieson put it, the first complex cell crossed some intangible line that separates the non-living from the living.

Lahey began climbing the wall—up on the thrusters, then backward. Jamieson discovered a new species of snailfish, a long, gelatinous creature with soft fins, by looking through a viewport. The pressure eliminates the possibility of a swim bladder; the lack of food precludes the ossification of bones. Some snailfish have antifreeze proteins, to keep them running in the cold. "Biology is just smelly engineering," Jamieson said. "When you reverse-engineer a fish from the most extreme environments, and compare it to its shallow-water counterparts, you can see the trade-offs it has made."

The wall climb took an hour. When the last lander surfaced, Jamieson detached the camera and found that it had captured footage of a dumbo octopus at twenty-three thousand feet—the deepest ever recorded, by more than a mile.

The Pressure Drop set off toward the Pacific Ocean. McCallum lowered the pirate flag. Seven weeks later, Jamieson received a letter from the Indonesian government, saying that his research-permit application had been rejected, "due to national security consideration."

Buckle sailed to Guam, with diversions for Bongiovanni to map the Yap and Palau Trenches. Several new passengers boarded, one of whom was unlike the rest: he had been where they were going, six decades before. Hadal exploration has historically prioritized superlatives, and an area of the Mariana Trench, known as the Challenger Deep, contains the deepest water on earth.

On January 23, 1960, two men climbed into a large pressure sphere, which was suspended below a forty-thousand-gallon tank of gasoline, for buoyancy. One of them was a Swiss hydronaut named Jacques Piccard, whose father, the hot-air balloonist Auguste Piccard, had designed it. The other was Don Walsh, a young lieutenant in the U.S. Navy, which had bought the vehicle, known as a bathyscaphe, and modified it to attempt a dive in the Challenger Deep.

The bathyscaphe was so large that it had to be towed behind a ship, and its buoyant gasoline tank was so delicate that the ship couldn't travel more than one or two miles per hour. To find the dive site, sailors tossed TNT over the side of the ship, and timed the echo reverberating up from the bottom of the trench. There was one viewport, the size of a coin. When the bathyscaphe hit the bottom, stirring up sediment, "it was like looking into a bowl of milk," Walsh said. A half century passed before anyone returned.

The bathyscaphe never again dived to hadal depths. Jacques Piccard died in 2008. Now Don Walsh, who was eighty-eight, walked up the gangway of the Pressure Drop. It was a short transit to the Mariana Trench, across warm Pacific waters, over six-foot swells.

Above the Challenger Deep, Vescovo pulled on a fire-retardant jumpsuit, and walked out to the aft deck. A gentle wind blew in from the east. Walsh shook Vescovo's hand. Vescovo climbed into the Limiting Factor, carrying an ice axe that he had brought to the summit of Mt. Everest.

Hatch secured, lift line down, tag lines released, towline out—pumps on. Vescovo wondered, Is the sub able to handle this? He didn't think it would implode, but would the electronics survive? The thrusters? The batteries? Besides Walsh and Piccard, the only other person to go to the bottom of the Challenger Deep was the filmmaker James Cameron, in 2012. Multiple systems failed at the bottom, and his submersible never dove deep again.

The depth gauge ticked past ten thousand nine hundred metres, thirty-six thousand feet. After four hours, Vescovo started dropping variable ballast weights, to slow his descent. At 12:37 P.M., he called up to the surface. His message took seven seconds to reach the Pressure Drop: "At bottom."

Outside the viewports, Vescovo saw amphipods and sea cucumbers. But he was two miles beyond the limits of fish. "At a certain point, the conditions are so intense that evolution runs out of options—there's not a lot of wiggle room," Jamieson said. "So a lot of the creatures down there start to look the same."

Vescovo switched off the lights and turned off the thrusters. He hovered in silence, a foot off the sediment bottom, drifting gently on a current, nearly thirty-six thousand feet below the surface.

That evening, on the Pressure Drop, Don Walsh shook his hand again. Vescovo noted that, according to the sonar scan, the submarine data, and the readings from the landers, he had gone deeper than anyone before. "Yeah, I cried myself to sleep last night," Walsh joked.

The Triton team took two maintenance days, to make sure they didn't miss anything. But the Limiting Factor was fine. So Vescovo went down again to retrieve a rock sample. He found some specimens by the northern wall of the trench, but they were too big to carry, so he tried to break off a piece by smashing them with the manipulator arm—to no avail. "I finally resorted to just burrowing the claw into the muck, and just blindly grabbing and seeing if anything came out," he said. No luck. He surfaced.

Hours later, Vescovo walked into the control room and learned that one of the navigation landers was stuck in the silt. He was in despair. The lander's batteries would soon drain, killing all communications and tracking—another expensive item lost on the ocean floor.

"Well, you do have a full-ocean-depth submersible" available to retrieve it, McCallum said. Lahey had been planning to make a descent with Jonathan Struwe, of the marine classification firm DNV-GL, to certify the Limiting Factor. Now it became a rescue mission.

When Lahey reached the bottom, he began moving in a triangular search pattern. Soon he spotted a faint light from the lander. He nudged it with the manipulator arm, freeing it from the mud. It shot up to the surface. Struwe—who was now one of only six people who had been to the bottom of the Challenger Deep—certified the Limiting Factor's "maximum permissible diving depth" as "unlimited."

The control room was mostly empty. "When Victor first went down, everyone was there, high-fiving and whooping and hollering," Buckle said. "And the next day, around lunchtime, everyone went ‘Fuck this, I’ll go for lunch.’ Patrick retrieves a piece of equipment from the deepest point on earth, and it's just me, going, ‘Yay, congratulations, Patrick.’ No one seemed to notice how big a deal it is that they had already made this normal—even though it's not. It's the equivalent of having a daily flight to the moon." McCallum, in his pre-dive briefings, started listing "complacency" as a hazard.

Vescovo was elated when the lander reached the surface. "Do you know what this means?" McCallum said to him.

"Yeah, we got the three-hundred-thousand-dollar lander back," Vescovo said.

"Victor, you have the only vehicle in the world that can get to the bottom of any ocean, anytime, anywhere," McCallum said. The message sank in. Vescovo had read that the Chinese government has dropped acoustic surveillance devices in and around the Mariana Trench, apparently to spy on U.S. submarines leaving the naval base in Guam; he could damage them. A Soviet nuclear submarine sank in the nineteen-eighties, near the Norwegian coast. Russian and Norwegian scientists have sampled the water inside, and have found that it is highly contaminated. Now Vescovo began to worry that, before long, non-state actors might be able to retrieve and repurpose radioactive materials lying on the seafloor.

"I don't want to be a Bond villain," Vescovo told me. But he noted how easy it would be. "You could go around the world with this sub, and put devices on the bottom that are acoustically triggered to cut cables," he said. "And you short all the stock markets and buy gold, all at the same time. Theoretically, that is possible. Theoretically."

After a maintenance day, Lahey offered to take John Ramsay to the bottom of the trench. Ramsay was conflicted, but, he said, "there was this sentiment on board that if the designer doesn't dare get in it then nobody should dare get in it." He climbed in, and felt uncomfortable the entire way down. "It wasn't that I actually needed to have a shit, it was this irrational fear of what happens if I do need to have a shit," he said.

Two days later, Vescovo took Jamieson to the bottom of the Mariana Trench. They returned with one of the deepest rock samples ever collected, after Vescovo crashed into a boulder and a fragment landed in a battery tray.

Buckle started sailing back to Guam, to drop off Walsh, Vescovo, and the Triton crew. "It's quite mind-blowing, when you sit down and think about it, that, from the dawn of time until this Monday, there were three people who have been down there," he said. "Then, in the last ten days, we’ve put five more people down there, and it's not even a big deal."

It was early May, and there was only one ocean left. But the deepest point in the Arctic Ocean was covered by the polar ice cap, and would remain so for several months. The Pressure Drop headed south, toward Tonga, in the South Pacific. Bongiovanni kept the sonar running twenty-four hours a day, and Jamieson carried out the first-ever lander deployments in the San Cristobal and Santa Cruz Trenches. "The amphipod samples are mostly for genetic work, tracking adaptations," he told me. The same critters were showing up in trenches thousands of miles apart—but aren't found in shallower waters, elsewhere on the ocean floor. "How the fuck are they going from one to another?"

Bongiovanni mapped the Tonga Trench. The sonar image showed a forty-mile line of fault escarpments, a geological feature resulting from the fracturing of an oceanic plate. "It's horrendously violent, but it's happening over geological time," Jamieson explained. "As one of the plates is being pushed down, it's cracking into these ridges, and these ridges are fucking huge"—a mile and a half, vertical. "If they were on land, they’d be one of the wonders of the world. But, because they’re buried under ten thousand metres of water, they just look like ripples in the ocean floor."

Bongiovanni routinely stayed up all night, debugging the new software and surveying dive sites, so that the Limiting Factor could be launched at dawn. "Day Forever," she dated one of her journal entries. "Sonar fucked itself." Now, before taking leave, she taught Erlend Currie, who had launched Jamieson's makeshift lander in the Diamantina Fracture Zone, how to operate the EM-124.

"When you give people more responsibility, they either crumble or they bloom, and he blooms," Buckle said. In the next month, Currie mapped some six thousand nautical miles of the ocean floor, from the Tonga Trench to the Panama Canal. "Erlend's doing a good job," another officer reported to Bongiovanni. "He's starting to really talk like a mapper. He just hasn't quite learned how to drink like one."

I boarded the Pressure Drop in Bermuda, in the middle of July, seven months into the expedition. The crew had just completed another set of dives in the Puerto Rico Trench, to demonstrate the equipment to representatives of the U.S. Navy and to the billionaire and ocean conservationist Ray Dalio. (Dalio owns two Triton submarines.) Vescovo hoped to sell the hadal exploration system for forty-eight million dollars—slightly more than the total cost of the expedition. During one of the demonstrations, a guest engineer began outlining all the ways he would have done it differently. "O.K.," McCallum said, smiling. "But you didn't."

We set off north, through the turquoise waters of the Gulf Stream. It would take roughly three weeks, without stopping, to reach the deepest point in the Arctic Ocean. But the Arctic dive window wouldn't open for five more weeks, and, as Vescovo put it, "the Titanic is on the way." For several nights, I stood on the bow, leaning over the edge, mesmerized, as bioluminescent plankton flashed green upon contact with the ship. Above that, blackness, until the horizon, where the millions of stars began. Sometimes there was a crack of lightning in the distance, breaking through dark clouds. But most nights the shape of the Milky Way was so pronounced that in the course of the night you could trace the earth's rotation.

The air turned foggy and cold. Buckle steered out of the Gulf Stream and into the waters of the North Atlantic, a few hundred miles southeast of the port of St. John's, Newfoundland. After midnight, everyone gathered on the top deck and downed a shot of whiskey—a toast to the dead. We would reach the site of the Titanic by dawn. At sunrise, we tossed a wreath overboard, and watched it sink.

A few years ago, Peter Coope, Buckle's chief engineer, was working on a commercial vessel that was affixing an enormous, deepwater anchor to an oil rig off the coast of Indonesia. The chain slipped over the side, dragging down one side of the ship so far that the starboard propeller was in the air. Water poured into the engine room, where Coope worked. It was impossible for him to reach the exit.

British ship engineers wear purple stripes on their epaulets. Many of them think of this as a tribute to the engineers on the Titanic, every one of whom stayed in the engine room and went down with the ship. Now Coope, whose father was also a chief engineer, resolved to do the same. "I saw my life blowing away," Coope recalled. "People say it flashes in front of you. I was just calm. I felt, That's it—I’ve gone." The bridge crew managed to right the ship after he had already accepted his fate.

The next day, Vescovo piloted the Limiting Factor down to the Titanic, with Coope's epaulets, and those of his father, in the passenger seat. The debris field spans more than half a mile, and is filled with entanglement hazards—loose cables, an overhanging crow's nest, corroded structures primed to collapse. ("What a rusting heap of shit!" Lahey said. "I don't want the sub anywhere near that fucking thing!") Large rusticles flow out from the bow, showing the directions of undersea currents. Intact cabins have been taken over by corals, anemones, and fish.

That evening, Vescovo returned the epaulets, along with a photograph of him holding them at the site of the wreck. Coope, who is sixty-seven, had come out of retirement to join this expedition—his last.

The Pressure Drop continued northeast, past Greenland and Iceland, to a port in Svalbard, an Arctic archipelago about six hundred miles north of Norway. Huge glaciers fill the inlets, and where they have melted they have left behind flattop mountains and slopes, crushed and planed by the weight of the ice. Most of the archipelago is inaccessible, except by snowmobile or boat. The population of polar bears outnumbers that of people, and no one leaves town without a gun.

McCallum brought on board two EYOS colleagues, including a polar guide who could smell and identify the direction of a walrus from a moving ship, several miles away. By now, McCallum had adjusted the expedition schedule ninety-seven times. The Pressure Drop set off northwest, in the direction of the Molloy Hole, the site of the deepest point in the Arctic Ocean. The least-known region of the seafloor lies under the polar ice cap. But scientists have found the fossilized remains of tropical plants; in some past age, the climate was like that of Florida.

It was the height of Arctic summer, and bitterly cold. I stood on the bow, watching Arctic terns and fulmars play in the ship's draft, and puffins flutter spastically, barely smacking themselves out of the water.

The sun would not set, to disorienting effect. When I met John Ramsay, he explained, with some urgency, that the wider, flatter coffee cups contained a greater volumetric space than the taller, skinnier ones—and that this was an important consideration in weighing the consumption of caffeine against the potential social costs of pouring a second cup from the galley's single French press.

Ice drifted past; orcas and blue whales, too. Buckle sounded the horn as the ship crossed the eightieth parallel. One night, the horizon turned white, and the polar ice cap slowly came into view. Another night, the ice pilot parked the bow of the ship on an ice floe. The Pressure Drop had completed one and a half laps around the world, to both poles. The bow thruster filled the Arctic silence with a haunting, mechanical groan.

Bongiovanni and her sonar assistants had mapped almost seven hundred thousand square kilometres of the ocean floor, an area about the size of Texas, most of which had never been surveyed. Jamieson had carried out a hundred and three lander deployments, in every major hadal ecosystem. The landers had travelled a combined distance of almost eight hundred miles, vertically, and captured footage of around forty new species. Once, as we were drinking outside, I noticed a stray amphipod dangling from Jamieson's shoelace. "These little guys are all over the fucking planet," he said, kicking it off. "Shallower species don't have that kind of footprint. You’re not going to see that with a zebra or a giraffe."

The earth is not a perfect sphere; it is smushed in at the poles. For this reason, Vescovo's journey to the bottom of the Molloy Hole would bring him nine miles closer to the earth's core than his dives in the Mariana Trench, even though the Molloy is only half the depth from the surface.

On August 29th, Vescovo put on his coveralls and walked out to the aft deck. The ship and submarine crews had so perfected the system of launch and recovery that, even in rough seas, to an outsider it was like watching an industrial ballet. The equipment had not changed since the expedition's calamitous beginnings—but the people had.

"This is not the end," Vescovo said, quoting Winston Churchill. "It is not even the beginning of the end. But it is, perhaps, the end of the beginning."

He climbed inside the Limiting Factor. The swimmer closed the hatch. Vescovo turned on the oxygen and the carbon-dioxide scrubbers. "Life support engaged," he said. "Good to go."

For the first few hundred feet, he saw jellyfish and krill. Then marine snow. Then nothing.

The Triton crew piled into the control room. Lahey found a box of licorice from Svalbard, took a bite, and passed it around. "Just fucking heinous," he said, grimacing. "Who the fuck makes candy like that? Tastes like frozen shit."

There was a blip on the communications system. For a moment, the room went silent, as Vescovo called in to report his heading and depth. Then Kelvin Magee, the shop foreman, walked into the control room.

"Try it, Kelvin, you bastard!" Lahey said. "It's from Svalbard. It's local. It's a fucking Norwegian candy."

"Get it while there's still some left!"

"It's that ammonium chloride that really makes it—and that pork gelatine," Buckle said.

"Pork genitals?"

McCallum stood quietly in the corner, smiling. "Look at these fucking misfits," he said. "They just changed the world." ♦

An earlier version of this story misidentified the military hardware that Victor Vescovo considered installing on his ship and the kinds of marine organisms he encountered in the abyssal zone during the Southern Ocean dive.

By signing up, you agree to our User Agreement and Privacy Policy & Cookie Statement.

By Jeffrey Marlow

By Raffi Khatchadourian

By James Lasdun

By Nathan Heller