Nanda Devi’s lost nuclear device: How an Indian Army expedition found clues to a Cold War mystery

From the outset, there was little room for error. The 1993 expedition had been planned down to the smallest detail, save for one indulgence: a stroll through New Delhi’s Connaught Place to buy an audio cassette. The cassette carried Raag Malhar, a classical raga long associated with the 16th-century Mughal-era musician Tansen and the arrival of the monsoon.

“Whenever I played it at the Nanda Devi base camp, it would start to rain. It became a running joke among the climbers, so eventually I stopped playing it altogether. Perhaps I should not have carried the music at all,” says Major General Vinod K. Bhatt (retd), who was with the Army’s Corps of Engineers. Bhatt led that expedition to Nanda Devi, the sacred peak in the Himalayas. The expedition was officially described as “A Scientific and Ecological Expedition to Nanda Devi”.

The mountain offered a strategic position to monitor the Lop Nor desert in northwestern China’s Xinjiang province. It was there, on October 16, 1964, that China conducted its first successful nuclear test, code-named Project 596, stunning the west which was under the belief that Beijing was still some distance away from acquiring the bomb.

India, too, was worried. New Delhi’s relations with Washington were not really warm, because of its close ties with Moscow. Yet, two consecutive years of drought had left India reliant on American food aid, which gave Washington a degree of leverage. More pressingly, the shadow of the 1962 war with China still loomed large; New Delhi remained deeply wary of its neighbour’s expanding military prowess.

According to declassified CIA documents, India was already allowing the US to use an abandoned World War II airbase at Charbatia in Odisha for U-2 spy-plane operations to monitor China. After the Chinese nuclear test, the CIA turned to India’s Intelligence Bureau, then responsible for both domestic and external intelligence (the Research and Analysis Wing was formed in 1968). The request was for help in installing a listening device on Nanda Devi to detect signals from future Chinese nuclear and high-altitude missile tests. The CIA called the plan Operation High Altitude Test, or HAT.

A joint team of Indian and American climbers was assembled and sent for training on Mount McKinley in Alaska. Their task was to scale Nanda Devi and fix the listening device near its summit.

The equipment itself comprised sensors, transceivers to relay data to a base station (there was a telemetry post about 60km away) and a six-foot antenna to pick up radio signals from China. Since it had to run continuously, it needed a dependable power source and the Americans opted for a SNAP-19C (System for Nuclear Auxiliary Power) radioisotope thermoelectric generator, which converted heat from radioactive decay into electricity. Inside were seven capsules containing plutonium-238, an isotope with a half-life of about 88 years; the isotope was highly radioactive and could cause cancer if inhaled or ingested.

The climbing team was led by Captain M.S. Kohli, the celebrated mountaineer who died in June last year. Then a lieutenant commander in the Navy, he was assigned to the Indo-Tibetan Border Police. Along with him were Sonam Wangyal, Sonam Gyatso, Harish Rawat and G.S. Bhangu, drawn largely from the newly formed Special Frontier Force or Establishment 22, comprising Khampa warriors of Tibetan origin.

The expedition began in September 1965. On October 16, with the summit almost within reach, a fierce blizzard forced Kohli to abandon the climb. The team left the listening device in a sheltered spot, intending to retrieve it once conditions improved, but winter closed in and the recovery had to wait for the next season.

When the climbers returned, the device had vanished. Repeated searches in the years that followed turned up nothing.

Speaking to this correspondent in 2021, Kohli described the effort to find it: “We worked very hard for three years from 1966, but in vain. I was posted at Tapovan (in Chamoli district of present-day Uttarakhand) through that period, along with a scientist who tested the waters of the Rishi Ganga for radioactivity every single day. Eventually, the chief of the Atomic Energy Commission in Bombay called me. I told him the generator, with its seven capsules, could have run hot enough that it may have melted through some 30 metres of snow and struck rock at the bottom. We concluded that recovery was not possible, and we hoped nothing would come of it.”

After a report about the failed expedition was published by the American magazine Outside in April 1978, it caused an uproar in India and came up for discussion in Parliament. Prime minister Morarji Desai subsequently tasked a team of six scientists—Atma Ram, Homi Sethna, M.G.K. Menon, Raja Ramanna, V. Ramalingaswami and A.K. Saha—with assessing the risk. Desai tabled the report and its key findings in Parliament on May 18, 1979. The report judged the risk of a significant radiation hazard to be negligible, while recommending further efforts to trace the device.

The disappearance also fuelled a more dramatic theory: that Indian scientists and intelligence officers had quietly recovered the plutonium-238 capsules to study the technology. The idea gained currency because, nine years later, India conducted its first nuclear test at Pokhran on May 18, 1974, codenamed Smiling Buddha. The theory does not withstand scrutiny, however. Smiling Buddha used plutonium-239, the fissile material needed to sustain a chain reaction, not the plutonium-238 used as a heat source in the Nanda Devi generator. As Dr Anil Kakodkar, former chairman of the Atomic Energy Commission, told THE WEEK: “In all possibility, Pu-238 was used in the Nanda Devi capsules, as it is self-heating and emits alpha particles. But it was plutonium-239 that was used in the 1974 Pokhran test.”

Nanda Devi was not the only Himalayan peak to host such a device. After the Nanda Devi setback, an identical device was successfully placed at the summit of Nanda Kot, a mountain adjacent to Nanda Devi. After realising that nuclear-powered units on high peaks were either too hazardous to leave behind or prone to sinking into ice, the unit was subsequently removed.

THE WEEK, in its issue dated October 13, 2024, reported that yet another device was installed near the Khardung La pass in Ladakh. Unlike the Nanda Devi device, it used a conventional generator and functioned for years before satellite surveillance rendered it redundant. Sonam Wangyal, then with the Intelligence Bureau, led the team that put it in place. “The device was connected to a data-collection point near Leh, since scientists and technicians found it too difficult to climb up to Khardung La itself to operate, repair and maintain it,” said Wangyal.

India’s role in the Nanda Devi operation was eventually acknowledged at the highest level. A declassified US state department memorandum records a conversation at the White House between Morarji Desai and president Jimmy Carter on June 13, 1978, in which the Nanda Devi episode came up. Desai said India had accepted responsibility because it had been done at Washington’s request. Carter expressed relief that neither leader had been personally involved in the original operation.

An earlier memorandum, sent by acting secretary of state Warren Christopher to Carter on April 14, 1978, was more direct. “Recent press stories reporting that the CIA placed two nuclear-powered monitoring devices in the Himalayas in the 1960s to monitor Chinese nuclear activity are correct in major aspects,” it noted, adding that one device had been lost in an avalanche and never functioned, while the other had operated for years before being removed. It also corrected claims that India had been kept entirely in the dark, though it conceded that the Desai government had not known of the operation until press reports surfaced. The document closed with Washington’s standard line: “We are taking the standard position that we do not comment on allegations relating to intelligence activities and that this should not be taken as a confirmation or denial of the story.”

For decades, the missing device remained one of the enduring mysteries of the Himalayas. The mystery intensified after mountaineering was banned in the Nanda Devi National Park in 1983, following growing concerns over the fragile ecology of the sanctuary and also because of its religious significance. The Nanda Devi Biosphere Reserve was notified in 1988.

So when the Army planned a fresh expedition to Nanda Devi in 1993 under Bhatt, it could not seek permission for a conventional summit attempt. The mission was framed as a scientific and ecological study. “After making numerous rounds of the ministry of environment and forests, we submitted that it was to be a scientific and ecological study, and only then did we gain the requisite clearance,” Bhatt says. “We had to include ecologists, geologists, botanists and biologists in the team. With porters, it grew to about 100 people.”

Its goals were to reach the summit, clear accumulated waste, study the mountain’s flora and fauna, and, more quietly, look for the missing device. Bhatt briefed his team accordingly, telling them that the lost equipment might still be somewhere on the slopes.

The 1993 team brought together the Army’s Corps of Engineers, the Wildlife Institute of India, the Salim Ali Centre for Ornithology and Natural History, World Wide Fund for Nature-India, the G.B. Pant National Institute of Himalayan Environment and the Botanical Survey of India. Funding was tight: the environment ministry gave Rs7.5 lakh, the Army’s mountain adventure wing Rs5 lakh and the youth affairs ministry Rs2 lakh. Private donors, too, chipped in. Mohan Meakin supplied apple juice, Dabur sent honey and Nestlé provided noodles and other rations.

The team began its expedition on May 2, 1993, and reached the base camp on May 15. At 4:35pm. on June 13, Major Amin Naik, the deputy leader of the expedition, became the first member to set foot on the peak. He later retired as a major general. He was followed by nursing assistant S.P. Bhatt, G.K. Sharma of the Military Engineer Services, Captain Anand Swaroop and Havildar Didar Singh. Swaroop retired as a colonel, while Didar Singh was subsequently made an honorary captain. It was the first time that five members of a single team had stood on the peak together.

The achievement was notable in itself, but the team had stumbled onto something far more consequential. Apart from hauling down about a tonne of accumulated rubbish and compiling a detailed report on the mountain’s ecology, they found fragments that would reopen the long-running mystery of the missing nuclear device: apparent components of the installation lost 28 years earlier. But crucial parts, including the plutonium fuel capsules, remained unaccounted for. It lent weight to the theory that the SNAP-19C’s heat had melted through the ice and carried the generator deep into the glacier.

The discovery was pure chance. On June 11, Major Rajesh Bhardwaj, the expedition’s doctor, was walking back from camp 1 to base camp when he noticed something glinting across a moraine. Says Bhardwaj, now the head of an ENT clinic in Delhi and a former president of the city’s association of otolaryngologists: “I was walking on the right side of a ridge of the moraine when I noticed a shiny, metal-coloured object emerging from the scree on the left edge. We had heard the CIA story and knew something was buried on these slopes. It looked inert, so I radioed General Bhatt, who told us that if it showed no activity, we should bring it back to base.” The object proved too heavy for Bhardwaj and the exhausted porters to carry.

Bhatt went down himself the following day, June 12, but found only one aluminium box. The other had disappeared due to glacial movement. He and his fellow engineers quickly realised they had found something extraordinary. “I held onto the secret for years. A few colleagues who knew about the recovery would coax me to reveal it, but I kept quiet, until now. It is time to bring it out in the open. Otherwise, history will not be kind to us.”

After returning to Delhi, the team held a display of the recovered material for a select group which included the then Army chief General Bipin Chandra Joshi, engineer-in-chief Lieutenant General V.N. Kapur and Captain Kohli himself, then president of the Indian Mountaineering Foundation. Bhatt recalls Kohli’s reaction: “He looked at the boxes, turned to me and asked, ‘Do you think this is what I think it is’? I asked if he meant the nuclear device. And he said, ‘This is it’.” Kohli, who had led the original CIA-IB expedition and spent years searching for the device, was arguably better placed than anyone to recognise it. “He told the Army chief that it would be best to keep the discovery under wraps, since it would otherwise turn into a political issue.”

The boxes were quietly removed and the discovery was never made public. “The story was hushed up. It was a decision conveyed verbally,” said Bhatt. The Army chief did insist the material be tested for radiation. It was sent to the Nuclear, Biological and Chemical Defence School (now known as the Joint Services Training Institute for Chemical, Biological, Radiological, and Nuclear Defence) under the College of Military Engineering in Pune. Bhatt says no radioactive contamination was found. It was then sent to the Bengal Engineer Group, also known as the Bengal Sappers, in Roorkee, Uttarakhand, for storage. “We took it off display, and no team member ever spoke about it again. In the Army, we operate on a need-to-know basis,” says Bhatt.

Nearly two decades later, on the eve of a farewell dinner at the Bengal Sappers Officers’ Mess in 2012, Bhatt wanted to see the stored material again. It could not be found. “Possibly it got sold off as scrap,” he says.

Even so, the discovery offers some reassurance on the question that has worried people most: radioactive contamination. Naik believes the aluminium casing they found was likely the outer shell of the SNAP-19C. “If that assessment is correct, the avalanche would have severely damaged the generator and separated its components, including the fuel capsules, from the casing. In any case, the SNAP-19C would have stopped functioning as a useful power source decades ago, since its designed life was only about two years.”

Plutonium-238 has a half-life of roughly 88 years, meaning much of the original material would still be radioactive today. More telling, perhaps, is that the 1993 expedition also collected snow, water and soil samples from across the glacier, and its report found no evidence of contamination, a significant finding given the sampling was carried out nearly three decades after the device vanished. “Even if the avalanche had damaged or separated the fuel capsules, any released material would have dispersed through an enormous glacier spanning kilometres and holding vast quantities of ice, snow and water,” says Naik. “The absence of detectable contamination in our samples is important field evidence that the lost SNAP-19C has not contaminated the Nanda Devi glacier or its waters.”

He also points out that the plutonium fuel was never simply exposed to the elements. It sat within its protective metal cladding—an inner tantalum layer and an outer casing of heat- and corrosion-resistant Haynes 25 alloy—through which the heat from radioactive decay passed to power the thermoelectric generator. “So even if the avalanche damaged or separated the outer aluminium casing, the individual fuel capsules would not necessarily have been breached. That matters a great deal in assessing the present risk,” says Naik.

The 1993 expedition filled in an important piece of the Nanda Devi nuclear puzzle without actually completing it. India’s second highest mountain after Kangchenjunga has given up part of its secret. It has not given up all of it.