NASA shows an “accidentally found” photo of a “city under the ice” of the US military in Greenland.

As NASA scientist Chad Greene flew north of Greenland with a team of engineers in April, they didn’t expect their radar to detect something man-made buried deep in the ice. Greene and his team were flying above the Greenland Ice Sheet in a NASA Gulfstream III aircraft, surveying the empty expanse of ice more than a kilometer deep in some places, when their radar instrument picked up something unusual.

“We didn’t know what it was at first,” Greene said in a statement released by NASA’s Earth Observatory this week, along with new images of the discovery. “We wanted a bed of snow and pops at Camp Century.”

It turns out that the group stumbled upon an abandoned Cold War-era military base built by the US Army Corps of Engineers in 1959. Dubbed the “city under the ice,” the group consists of a network of tunnels carved into the ice. It was abandoned in 1967 and, over time, was buried about 100 meters underground as snow and ice accumulated.

The site was built as part of Project Iceworm, a then-secret plan to build a missile launch pad under the Greenland Ice Sheet during the Cold War, when tensions were rising between the US and the then-Soviet Union. Camp Century, a remote, nuclear-powered installation, was built to study the feasibility of such a project, but it never materialized and the base was scrapped under the assumption that it would be buried forever under the ice.

Although the “city under the ice” had been captured by previous radar scans, instruments used on a NASA flight in April provided a more detailed, if unexpected, survey.

“In the new data, the individual structures of the secret city are visible in a way never seen before,” said Greene, who works with NASA’s Jet Propulsion Laboratory.

Previous scans have used a type of radar that points straight down and produces two-dimensional scans of structures buried beneath the ice. Greene’s flight used NASA’s Uninhabited Aerial Vehicle Synthetic Aperture Radar, which is capable of producing “multi-dimensional” maps, according to the agency.

An image released by NASA on Monday showed features of the base hidden deep in the ice, appearing as mysterious objects near the base of the ice.

“Scientists used maps obtained by conventional radar to confirm Camp Century’s depth measurements – part of an effort to measure when the melting and shrinking of the ice sheet could re-expose the camp and any remaining biological, chemical, and radioactive debris that was buried along with it,” said NASA’s Earth Observatory on its topic this week. “The scientific application of the new UAVSAR image of Camp Century remains to be seen; for now, it remains a chance discovery.”

A 2016 study of the abandoned site suggested the facility could no longer be considered “perpetually preserved,” due to climate change increasing the rate of Arctic ice melt.

CBS News’ Walter Cronkite visited Camp Century to visit an undeveloped site in a program that aired in 1961. The camp manager, Captain Tom Evans, explained to him that the goals of the program were threefold: “The first is to test a number of promising new concepts for polar construction. And the second is to provide a practical field test for this new Greenland nuclear facility, where scientists can continue their R&D activities.”

The actual nature of that research and development was not discussed in Cronkite’s report for the CBS documentary show “The Twentieth Century.” (An abridged version of that report can be viewed at the link above.)

Speaking to 60 Minutes in 2016, as the show revisited Cronkite’s decades-long journey to Camp Century, producer Daniel Ruetenik said the trip was fascinating, and he was surprised by the resurgence of interest in the vast, frozen Greenland Ice Sheet.

“At that time [of Camp Century]the Cold War was seen as the greatest threat to humanity,” said Ruetenik. So, there is a second purpose now. “