On a clear, cold day in May 1959, two U.S. Army officers clad in polar gear gazed through their aviator sunglasses at the endless white horizon before them. Standing heroically in front of Arctic personnel carriers, Col. John Kerkering and Capt. Thomas Evans took measurements for a new military installation to be buried beneath Greenland’s ice cap. They called it “Camp Century.”

The proposed facility in northwestern Greenland was publicly touted as a “nuclear-powered Arctic research center” nestled in a wilderness of ice and snow. But the real reason for this Cold War base was to build and maintain a secret network of tunnels and missile silos connected by rail cars known as “Operation Iceworm.”

It was the tense days of the Cold War when a rivalry between the nuclear powers of United States and the Soviet Union had military leaders constantly scheming new ways to outfox the other side. Pentagon planners thought that by shuttling 600 nuclear-tipped “Iceman” missiles (a new moniker for the existing Minuteman) back and forth between 2,100 silos, they could keep their counterparts in the Soviet Union guessing. Imagine a potentially deadly game of atomic “whack-a-mole” spread out across 52,000 square miles of northern Greenland.

“We needed a flat surface, a level with less than one degree of slope,” Evans says in a voiceover of a U.S. Army film, released in 1960, documenting the scout mission for the site. “This would minimize construction problems by enabling us to keep all of our tunnels on the same level.”

Once the location was settled, hundreds of military engineers and technicians trekked 150 miles from the existing Thule Air Base along Greenland’s northwest coast to the Camp Century site. From 1959 to 1961, they dug hundreds of feet into the compacted snow, fashioning an underground city with a sleeping quarters, laboratories, offices, a barber shop, laundry, library and warm showers for 200 soldiers.

The American public didn’t know about Project Iceworm until a Danish Parliament investigation published documents about the secret project in 1997, but they did know about Camp Century. Television crews and journalists from National Geographic and the New York Times visited as the camp took shape. So, too, were an unlikely pair of Boy Scouts, one from Kansas and one from Demark. They won a contest to visit Camp Century and their letters and diary entries sent home revealed much about the daily life in their frozen, underground city, according to Kristian Nielsen, head of the Centre for Science Studies at Denmark’s Arhaus University.

Nielsen also found accounts that soldiers living underground worried about exposure to radiation from a nuclear reactor that powered the station. “We had a hard time finding out about this,” Nielsen says. “It was a concern for them.”

The underlying public message of Camp Century was to show how ordinary Americans (albeit soldiers) could live and work in a remote location, almost as a stepping stone to a space colony. Army researchers did perform some science, including drilling the first ice core to the base of the Greenland ice sheet, a core that provided information to scientists about the past climate. All the while, however, planners back at the Pentagon were trying to figure out how to use Camp Century to coordinate a secret missile installation.

Despite the Cold War propaganda and amazing feats of engineering, the ice-bound underground installation ultimately didn’t work. Operation Iceworm was shut down because the walls of snow and ice kept moving, squeezing the tracks that carried the missile train. Problems with the nuclear reactor forced its removal in 1964 and by 1966, the Army had abandoned Camp Century altogether.

Nielsen says the experiment also failed because of politics. Danish officials had a policy of no nuclear weapons on Danish soil, even though it allowed the U.S. military to use Greenland as a staging area. And a Pentagon dispute erupted between generals at the Army—who wanted their own missile system at Camp Century—against Air Force and Navy officials who wanted control over positioning of the nation’s nuclear missiles.

“It was a turf battle,” he says.

Camp Century was shuttered, and engineers figured that ice would eventually entomb the abandoned station. But decades later, warming temperatures under climate change presented a problem. In 2016, a team of scientists reported that the rapid warming of the Greenland ice sheet could lead to the exposure of radioactive, toxic and human waste that remains at Camp Century, possibly leaking into the streams that lead to the ocean.

“It’s just a matter of time,” says Mike MacFerrin, an author on the 2016 study that exposed the problem. “When the water reaches these wastes and gets to the coast, then we’ve got a big problem.”