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When his phone rang, Ben Reymenants, 45, was packing his dive gear. Reymenants is one of the most sought-after tech diving instructors in Southeast Asia. He’s in the water 300 days a year and has written multiple manuals on tech diving, which utilizes specialized training, equipment, and gas mixtures to enable divers to go much deeper and stay down longer than recreational scuba divers. The Belgian national once set an open-water depth record. When record-breaking tech divers crave further instruction, they find Reymenants.
He’d spent much of his season working six or seven days at a time in and around the deep sea caves of southern Thailand for his business, Blue Label Diving. So Reymenants and his Dutch wife and business partner, Simone, decided to spend a week diving in the shallow reefs of the Philippines before returning home to Phuket, Thailand. That all changed when he answered the phone.
It was a cave diving buddy, Ruengrit Changkwanyuen, a regional manager for General Motors Thailand and a consultant with the Thai Navy SEALs. Changkwanyuen had been one of the first volunteers to show up at the mouth of the Tham Luang cave system, in the mountains along the Myanmar border, two days after a junior soccer team hiked inside with their 25-year-old assistant coach and didn’t return.
Like everyone in Thailand, Reymenants had been following the story. In Thai Buddhist culture, caves are sacred. Many are sprinkled with stupas and golden Buddha statues, which pilgrims visit to light candles, make offerings, meditate, and pray. For much of the year, the 6.4-mile underground network of chambers, tunnels, collapses, and dead ends that form the Tham Luang caves are navigable by foot, and it’s common to hike inside. The soccer team had visited the caves near the town of Chiang Rai many times before, and on June 23, they trekked more than a mile underground through three glittering chambers connected by long narrow corridors, called siphons. During the wet season from June to September, however, the Tham Luang Forest Parkbecomes saturated. Heavy rains leak into the cave from all sides and swallow up every inch of airspace. At some point while the team was hiking, the cave was inundated with a flash flood, forcing the boys and their coach to higher ground and cutting off their escape.
When the news broke on June 24, Reymenants contemplated catching a plane to Chiang Rai, but then the Thai Navy SEALs showed up en masse, followed by a team of renowned English cave divers. The boys, it seemed, were in capable hands.
Changkwanyuen told him that circumstances had changed. He said that in the initial 24 hours, the SEALs made good progress. They worked their way through three main chambers. Each was wide enough to include dry ground jutting with stalagmites. The vaulted ceilings provided plenty of airspace. As they ventured deeper, the SEALs strung guidance, radio, and power lines so they could have a base of operations as close as possible to wherever the soccer team was located. They also sketched maps to determine where they had been and where they might still need to search.
When the divers reached the third and final chamber, they made a discovery: a pile of cleats and backpacks. They could see footprints leading toward a siphon hemorrhaging floodwater. If the kids were alive, they had to be somewhere beyond that corridor. That third chamber became divers’ base camp.
A platoon of SEALs geared up to penetrate the 650-foot-long siphon. Visibility was a few inches, and at the very end, they reached a vortex—a whirlpool fed by a confluence of currents from opposite directions. Nobody realized it yet, but they’d reached a pivotal T-junction and were just a quarter to half a mile from finding the kids. As they searched for a tunnel to take them deeper inside, the force of the water shoved them right, where they found an opening and entered another corridor until they reached a cramped bottleneck and turned back. That’s when the weather turned against them. A second deluge flooded out all their progress and cost the divers an additional half-mile of navigable airspace. That underwater T-junction—and the tunnel leading toward the kids—was farther away, and there was no guarantee the divers would be able to find it again. Changkwanyuen wanted Reymenants to help them find their way back.
Reymenants hopped a plane from Phuket to Chiang Rai at 6 a.m. on June 26. When he landed, police drove him to the mouth of the Tham Luang cave. A village of hundreds of media and volunteers had sprouted at the entrance. There would soon be thousands. A team of Thai civil engineers was working to pump water and build containment dams, and local women prepared meals around the clock. Throngs came to keep vigil. Reymenants was led directly to the mouth of the cave. He’d never been there before, and the first thing he noticed was how beautiful it was. Then he came upon a team of SEALs on their way out after a fruitless underwater mission—and realized they weren’t even equipped for extreme cave diving.
He wasn’t shocked. Like in the United States, Thai Navy SEALs are mission-specific. The majority of their underwater work unfolds in the first 20 feet of depth, where they can breathe pure oxygen so they don’t exhale any bubbles in the water and can move unseen to plant depth charges or emerge on beaches in the dead of night. Among both American and Thai SEALs are a handful of divers who can plunge more than 600 feet by breathing mixed gases to perform extreme submarine recovery missions, but that skill set is not common.
There are two main categories of cave dives. Deep dives are what Ben Reymenants is known for. He regularly penetrates limestone caves in the Andaman Sea, where depths exceed 500 feet and where visibility can exceed 200 feet (with the proper lights). He’s been deeper than 700 feet below the surface, has come eyeball to nose with a new species of methane-eating worm, and has received manicures from a team of transparent shrimp on long ascents. But this wouldn’t be one of those dives. This was a long, or horizontal, dive. But since deep-water caves are often accessed via narrow siphons, Reymenants was both uniquely equipped and experienced to contribute.
An eighth-mile from the cave entrance, Reymenants arrived at the first chamber, strapped on his Triton 3 rebreather, slipped on his drysuit, and waded into hip-deep rapids. Immediately, he was swept off his feet and turned on his back like a helpless turtle. Nearby, Navy SEALs glared at him. Reymenants had been touted as a potential savior to what increasingly felt like a doomed mission, and he wasn’t inspiring much confidence. He shook his head, righted himself, grabbed the rope, and began pulling himself upstream against the flow.
“It was like fighting a hurricane while dragging your dive gear behind you,” Reymenants said via Skype. “Think of the worst CrossFit workout of your life.” Then add dirty water.
He navigated one siphon and came to the dry ground of the second chamber. Reymenants stripped off his gear and hiked up and over a rise 60 feet high before sliding down the other side. Then he suited back up and sank into the rapids again to charge through another long siphon. The third chamber included a dry hill that had become diver base camp. It looked like something out of the Himalayas. Oxygen and air cylinders were strewn about, along with water bottles and protein bar wrappers. The Navy SEALs were everywhere, radios chirping. Reymenants stepped to the edge of a flow that disappeared into the darkness. The water spun and frothed the color of a caffè latte. It had taken three hours for Reymenants just to reach the departure point of his first dive.
Reymenants planned to dive on oxygen and chose his drysuit so he could stay in the 69-degree water for up to four hours. He also brought multiple lamps—dive lights burn out quickly, and he couldn’t chance being left in the dark. Before Reymenants submerged, he’d received a briefing and studied available maps. The SEALs were working off satellite maps and their own sketches, but Reymenants and the English team were partial to the maps drawn by dry cavers. A French team was the first to map the Tham Luang cave 30 years ago. In 2015, those maps were updated by two English-born geologists. Reymenants had spoken to one of them before his initial dive, and everyone agreed they needed to find that T-junction again. If they could find it, everyone was confident they would find the kids.
“That first dive was a total disaster,” Reymenants said. His drysuit ripped, he smashed one of his dive computers against a rock as he fought his way forward, and the maps he’d read were drawn by people walking along the floor, not swimming near the roof. Even in areas where there was a foot or two of airspace, it was nearly impossible to find any familiar structure to work from. Underwater visibility was nonexistent. Reymenants covered a distance of 500 feet and laid line with his typical cave reel; it was the only line he had at his fingertips when he left Phuket, but it was just one millimeter thick. Such a thin line is useful in deep water or when currents are stable, but he knew the line could snap at any moment in what amounted to Class III water. If it did, Reymenants or whoever was upstream of the break would be in deep shit.
He climbed out of the water back at camp three roughly four hours after his dive began and consulted with the English dive team. Led by Rick Stanton and John Volanthen, the group made headlines in 2004 when they found a crew of six British soldiers who had been trapped in a flooded cave in Mexico for six days. That was the first of several high-profile rescue and recovery missions; they are widely regarded as among the best cave divers on earth. Reymenants, Stanton, and Volanthen all agreed that they were hip-deep in a suicide mission. Nobody was sure if the kids and their coach were still alive, but they were certain more lives would be lost if they kept searching under the current conditions. Reymenants had been living in Thailand for 18 years, so he approached Navy SEAL command to break the news. But the commander wouldn’t call off the search.
“They couldn’t and wouldn’t just let the boys die. They made it clear that they would keep searching with or without our help,” Reymenants said.
Reymenants glanced over at a group of SEALs resting against the cave wall; some of them were as young as 19. He asked his liaison to find thicker rope.
The next day, Reymenants was back in the water. This time, he wore a more durable wetsuit instead of a drysuit and was joined by fellow cave explorer Maksym Polejaka, who had flown in to help. They carried 650 feet of thick rock-climbing rope, sourced by the SEALs and stuffed into a bag—the whole thing weighed 40 pounds. Reymenants was still on his rebreather. Polejaka was diving on air and dragged five tanks along with him. By then, the engineers had made progress with a plan to dam the inflow and pump water out of the caves. Water levels had receded and visibility improved to a few feet as a result, and the divers could surface every 300 feet to communicate. They were still swimming near the ceiling, however.
“It was like being a bird in a house,” Reymenants said. “We had to rediscover every meter of that cave. There was a lot of trial and error. We were feeling our way through.” Yet by the time they made their way back to base camp in the third chamber, they had laid all 650 feet of line and taken compass bearings, which the SEALs used to verify that, at long last, they were on their way back toward the T-junction.
The English divers dropped in next and were able to link Reymenants’ and Polejaka’s line with the original line that the Navy SEALs tied off on day one—another big breakthrough. When they dropped in again, Reymenants and Polejaka each carried two bags of rope. They followed the original SEAL line to its end, and then pushed farther. “Your head becomes your greatest enemy,” Reymenants said. “You start to think, ‘Am I going the right way? Will I ever find my way back? Will the restrictions get worse?’”
They made strong progress until they reached that vortex and their visibility receded from feet to inches. They were shoved right. Reymenants dove down, found an opening, and continued through a corridor that became increasingly narrow and muddy until he could no longer move forward or back. He was stuck. Adrenaline surged through his body. His heart pounded. Reymenants tried to relax, because when breathing gas, elevated heart and respiratory rates deplete air supply.
“[Polejaka] could tell something was horribly wrong when he heard strange noises coming from my rebreather,” Reymenants said. Polejaka tugged hard on Reymenants’ lower legs and with a lot of struggle and effort was able to pull him back against a stiff current, inch by inch, for a total of 50 feet. It wasn’t all bad news: Reymenants suspected they’d been sucked into the same bottleneck as the Thai SEALs. If that was true, then they had found the T-junction.
Together, Reymenants and Polejaka resurfaced in an air pocket. The effort had drained Polejaka’s tanks, and he needed to turn around, but Reymenants still had one more bag of line. He recalled a recent conversation with Robert Harper, one of the British cave explorers who remapped the cave in 2015. He’d warned of dead ends but said if Reymenants reached a big room with an air pocket and could find a gravel pathway, he should follow it against the current. Reymenants dropped down to the bottom. Again, the current forced him right, but he fought hard and found a gravel path and with it a colder stream of water. He followed the gravel into a restriction. According to Harper, the proper siphon would be shallow yet wide. This one appeared to be three feet high and about ten feet across, which fit the description. He unfurled and tied off his line and took a compass bearing, then swam back to his friend. Reymenants was 99 percent sure that he and Polejaka had found and pushed past the T-junction. If he was right, the kids were just several hundred feet beyond the end of his rope.
When they surfaced together at base camp, the SEALs confirmed that Reymenants’ compass bearings matched those from their original trip to the T-junction. They had the breakthrough they were looking for. The English team suited up and dropped in. Four hours later, on July 2, the English divers called out from the front of the cave: They’d found the 12 kids and their coach—alive. The commander of the Thai SEALs found Reymenants and pulled him in for a bear hug.
Celebration faded into concern. The boys had been living in a moist cave environment, breathing air with oxygen levels hovering at 15 percent for ten days. With bad weather creeping into the forecast, there was pressure to act. For days, divers and soldiers prepared and rehearsed the potential recovery. One man, Saman Kunan, a retired Navy SEAL who worked in airport security, died on July 6 while placing oxygen canisters along the line in a siphon. His death was mourned even as 24 men formed a chain and for three days and nights pulled the boys and their coach from the darkness back to life.