May 18, 2016 4:00 AM EDT

Nine men line up on a deck along the Tonlé Sap Lake in Cambodia. The directive is clear. They are to dive blindly into the murky depths of up to 100-feet, against the strong river currents, to find and recover undetonated explosive devices. Barring the safety hazards of a potential underwater blast, there’s one glitch: none of them can swim.

“There was a lot of flailing around in the water during those first training sessions,” British photographer Charles Fox tells TIME. “Cambodians generally aren’t taught the skill of swimming and some struggled just to keep their head above the water.”

It has been over 30 years since the end of the Khmer Rouge regime, which resulted in the deaths of an estimated two million people. Ships carrying large stockpiles of explosives to supply the Khmer Republic were sunk in the Mekong and Tonlé Sap rivers in the 1970s. The small country also became the stage for a massive carpet bombing by the United States during the Vietnam War. Today, Cambodia is still picking up the pieces of this dark legacy—literally. Abandoned land mines remain a deadly and hidden threat that still kill or injure more than 100 people each year.

Three years ago, Fox picked up a newspaper in a coffee shop in Cambodia, where he found an advertisement from the Cambodian Mine Action Centre (CMAC) calling for mine action sensors to be trained to search rivers for bombs. “I thought ‘this is it,’” he says. “This brief, ridiculous 100-word ad is the beginning of my next story.”

Forty hopeful volunteers responded to the ad, from which CMAC selected a team of nine de-miners to become Cambodia’s first elite salvage diving unit. Three years later, Fox says their swimming skills have improved dramatically.

“They went from a group of guys in swim trunks to the greatest underwater diving team in the region,” Fox says. “They have a remarkably cohesive unity and take pride in what they do.”

The de-miners undergo a rigorous military boot camp. Through drills, diver tests and competitions, they learn underwater detonation, explosive identification, rescues and surveillance. They train to dive blindly into water that is black just six feet below the surface, identifying explosives by touch alone.

The dangers of tampering with explosive devices that have been dormant for 40 years elude no one. If a device goes off beneath the surface, shock waves would travel faster than the speed of sound, instantly killing anybody in the water.

“You gain confidence from the divers,” says Fox. “You read their level of assurance because they know what they’re doing.”

Fox has been following the divers for three years, swimming with them and staying after training sessions, learning more about the reasons why each of them dives. Many see it as a patriotic duty. Others have cleared explosives from the land and feel the responsibility to finish the job in the rivers. All hope to use these skills for a similar line of work in the future.

“This story took an unexpected turn,” Fox says. “Beyond the environmental aspect, I became drawn to the human aspect of the piece. As the threat of explosives decreases, I hope this project helps offer these guys a realistic future for work in Cambodia or internationally.”

Charles Fox is a photographer currently based in Phnom Penh, Cambodia.

Rachel Lowry is a writer and contributor for TIME LightBox. Follow her on Twitter and Instagram.

Contact us at letters@time.com.

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