Back in the day, America's spies didn't have the kind of surveillance satellites that can pinpoint you from orbit. The CIA had to rely on much rougher methods like climbing the Himalayan mountains. In theory, it was an ideal place to put sensor devices and spy on China. It also nearly ended in complete failure.

It was 1965, and the Pentagon and CIA were worried. The Vietnam War was beginning to ramp up. The People's Republic of China had recently conducted its first nuclear test, but intelligence was limited. Chinese missile tests were being conducted at a secretive facility a few hundred miles north of the Himalayan mountains, but intelligence estimates for the missiles' range -- and compatibility with nuclear warheads -- was unclear. The mountain range blocked ground-based sensors, which could have picked up the missiles' radio telemetry signals. Worse, Pakistan had just kicked out America's spy planes, and precision satellite imagery was still primitive.

View more

There was another option. Two years prior, the first successful American expedition to the summit of Mount Everest had completed its trip with a small team of Sherpa guides. Gen. Curtis "Bombs Away" LeMay, the Air Force's top officer and who secured some funding for the 1963 expedition, wanted to know if the mountaineers would go back.

"Le May was wondering if these hardy Sherpa people -- who had worked in support of the 1963 expedition -- and the members themselves might be interested in participating in a clandestine operation," Broughton Coburn, author of the book The Vast Unknown: America's First Ascent of Everest, tells Danger Room. Their job: carry a plutonium-powered generator -- known as a SNAP unit -- and a sensor device to a Himalayan peak high enough to secure a direct line of sight to where China's missiles were flying. Once at a suitable summit, the team would assemble the device and aim it towards China.

But the expedition ran into several problems. Everest was out of the question, as the mountain bordered China, leaving a surveillance device vulnerable to being discovered by a potential Chinese summit attempt. Nanda Devi, a 25,645-foot mountain within Indian territory was picked instead with the cooperation of Indian intelligence. However, the expedition was forced to abandon a summit attempt under heavy snowfall and declining oxygen levels. "They stashed the equipment in a crevice and anchored it with the expectation they would return the following spring, carry it to the summit and piece it together to make it operational," Coburn says.

Then it got worse. A follow-up Indian expedition to retrieve the device discovered it had gone missing, apparently having slid down the mountain in a landslide, carrying its plutonium with it. The job of finding and replacing it then fell to another group of Everest veterans, freshly recruited from the United States. One of the members interviewed for Coburn's book -- physician and mountaineer Dave Dingman -- has not previously spoken about his role in the spy mission.

/Flickr

According to Coburn and Dingman, the CIA flew Dingman and other members of the expedition to a remote island in the South Pacific for bomb practice. "The teachers were soldier of fortune-type characters," Dingman said. "About ten of us recruits gathered around a large table and fashioned charges from C-4 plastic explosives and duct tape. The instructor observing our progress said something I have never forgotten: 'Remember, gentlemen: A neat bomb is a happy bomb."

For several months in 1966, the expedition would fly aboard boxy HH-43 Huskie helicopters flown by Air Force pilots and suitable for high-altitude operations. Sitting in the rear of the choppers, Dingman and his team members scanned Nanda Devi with neutron detectors. "There's some evidence that the whole hillside, the whole area where it had been stashed had slid away in a landslide and carried the device downhill," Coburn says. There was no sign. The mission was abandoned.

"No readings, no leads where the device might have fallen," Coburn adds. "They believe they would have easily picked up a signal. And at least in the opinion of some of the climbers, they felt that Indian intelligence had secretly hiked up there before that spring mission and retrieved the device, and spirited it away, presumably in order to study it and possibly gather the plutonium, even though that would have been technically impossible, as I understand it."

The CIA eventually did get a SNAP unit and signal device installed the Himalayas, Coburn notes. In 1967, a group of climbers planted one below the summit of Nanda Kot, a 22,510-foot mountain nearby. It was buried in snow three months later and stopped working, although having gleaned enough data from Chinese tests to indicate -- at the time -- that Beijing didn't yet have a long-range nuclear warhead.

"Ultimately, this wild operation was successful in gaining at least that much information," Coburn says. Although the technique was obsolete by the time spy satellites emerged. Still, it was close, and somewhere down the mountain, a piece of Cold War plutonium might still be there.