This article is part of Engelsberg Ideas’ latest series, ‘The Nuclear World Transformed’, in which our writers explore the history and current state of the global nuclear landscape, and how it is being reshaped by a new age of great-power competition. 

Between 1990 and 2001 something happened in China that is unthinkable in today’s tense world. In short, an American wandered through the Chinese nuclear archipelago and came out to tell the tale. It sounds like a novel but it is a lesson in game theory and it is pure fact.

The American was the director of the Technical Intelligence Division at Los Alamos, Danny B. Stillman, and he was invited to visit China’s most secret nuclear weapons facilities no fewer than ten times. Some were hidden deep in mountainous valleys and in places so remote that during hard times under Mao Zedong the isolated experts had gone hungry.

Stillman was allowed to talk to scientists, look at equipment and discuss experiments. He was permitted to bring colleagues because he never travelled alone for security reasons. It was, he said, a remarkable unveiling of the Chinese nuclear weapons programme, a deliberate disclosure of its nuclear crown jewels to a central player in the American nuclear intelligence community. They knew exactly who he was.

Stillman confirmed all the details when I contacted him in the course of research for the Sunday Times on the veterans of China’s nuclear test programme, old men who had flown planes through radioactive clouds and scrubbed the aircraft down afterwards without protective gear. It chimed with the bleak conditions he had seen.

He co-authored a book, The Nuclear Express, with Thomas C. Reed, a nuclear weapons designer who was secretary of the US Air Force under presidents Ford and Carter, and later a special assistant to President Reagan. It was billed as a political history of the bomb and its proliferation.

The book was published in 2009 but did not get the attention it deserved. Perhaps that was because the authors were bleak-vision hawks (Stillman died in 2019, Reed died in 2024). It remains a rare authentic source, along with my notes of our exchanges.

Why did the Chinese invite an American to their atomic redoubt? Stillman concluded that one motive was deterrence, another was to prise out knowledge. A third was geopolitics. Intricate, flexible and smart, the Chinese game was made for the mind of a nuclear physicist.

In the late 1970s the People’s Republic had ‘opened up’ and turned to the West. One witness to the pivot was the young Xi Jinping, today’s leader, who served as private secretary to the defence supremo, Geng Biao. In those days, Moscow was the enemy.

A decade on, the Chinese and Americans had aligned in the proxy struggles of the late Cold War. Stillman’s first visit to China came in the aftermath of the Tiananmen Square massacre of 1989. Given the strained relations of the time, it was indeed remarkable.

He landed at Shanghai on 3 April 1990. The Americans started at Fudan University in the port city, then flew west to reach the weapons complex at Mianyang and the new ‘Science City’ nearby, a sprawl of laboratories and firing ranges. They went to a nuclear technology institute near Xi’an and to the test site at Malan in the desert wastes of Xinjiang.

It was eye-opening. At the time, wrote Stillman, the Chinese had only one operational supercomputer in the whole country. Yet they had simulated nuclear blasts, run implosion diagnostics and conducted sophisticated radioactivity analysis.

He learned that China had started with uranium bombs and only later moved on to use plutonium. They showed ‘an uncanny familiarity with US nuclear test procedures’. On his very first visit, a Chinese scientist referred to a highly classified laser and fission project at the Lawrence Livermore National Laboratory by its correct code name.

All was not reassuring. The Americans found that neither safety nor weapons security ‘were at the top of the Chinese nuclear priority list’. They did not think terrorism was a threat and entrusted protection to ‘politically reliable’ guards.

Stillman went back nine times until the exchanges were stopped when relations soured. The Americans had hosted reciprocal trips by Chinese scientists but none of these compared to stepping behind the bamboo curtain. The experience hardened Stillman’s opinions.

The Chinese, he said, had hoovered up papers, data and people across the open scientific community. They had built their atomic technology ‘one graduate student at a time’. Espionage, genius and singular purpose had allowed China to equal America’s nuclear weapons knowledge with actual tests numbering just four per cent of the US total.

The father of the Chinese bomb, Qian Sanqiang, studied in Paris under Frédéric Joliot-Curie, a pioneer of radiation studies and a member of the Central Committee of the French Communist Party. Qian returned to China in the 1950s with precision instruments and a message of support from Joliot-Curie and his wife Irène.

In 1959 Qian went to Dresden to debrief the atom spy Klaus Fuchs, just released from prison in Britain. Safe in East Germany, Fuchs described the design and operation of ‘Fat Man’, the bomb dropped on Nagasaki. The first Chinese A-bomb was tested at Lop Nur, in Xinjiang, on 16 October 1964.

Then there was Joan Hinton, a nuclear scientist who worked with Enrico Fermi and witnessed the Trinity test at Los Alamos. She became an ardent Maoist and moved to Beijing in 1966. The list of spies and collaborators leaves a modern strategist agape.

For hawks, Stillman and Reed’s book was a call to arms before its time. Their strategic message remains disturbing. As history, it has not been credibly challenged.

‘With the coming of the 1980s, Deng Xiaoping’s China apparently decided to actively promote nuclear proliferation in the Third World,’ they wrote. It was pure game theory to open up to America while arming America’s enemies, they argued.

They asserted that China handed warhead blueprints to Pakistan and tested a bomb on its behalf on 26 May 1990, eight years before the first acknowledged tests on Pakistani soil. Documents related to the device later turned up in Libya. American intelligence has since traced Chinese nuclear and missile technology sales, via North Korea, to Syria, Egypt, Yemen and Iran.

To the authors, Beijing was simply a reckless proliferator. It signed pacts like the Nuclear Non-Proliferation Treaty with no intention of keeping them. ‘Some within the Chinese government might not object to the destruction of New York or Washington, followed by the collapse of American financial power,’ they wrote.

Both Trump and Biden administrations woke up to the challenge. In October 2024 the US Defence Intelligence Agency (DIA) published its latest assessment of China’s breakneck nuclear modernisation programme under President Xi. It predicted that by 2030 Beijing would have more than 1,000 operational warheads, most of them capable of reaching the United States.

Xi has purged and reorganised his nuclear force. It is adding silo-based and mobile missile systems. The DIA said that China ‘very likely is also working to introduce a variety of completely new nuclear capabilities’ including a hypersonic glide vehicle with a range of 40,000 kilometres and low-yield battlefield warheads. It added that Russia is helping the Chinese to develop a ballistic missile early warning system.

To this mix add President Xi’s order to build two sodium-cooled fast-breeder reactors to produce plutonium, his decision to remove the country’s only known plutonium reprocessing plant from the civilian inventory and, said the DIA, a general line of ‘reduced transparency’.

China is officially committed to a ‘no first use’ policy. But it is also evolving a hair-trigger ‘launch on warning’ posture to enable a counterstrike before an enemy’s missiles arrive. The US and Russia operate the same way although it is fraught with risk. Then there are the politics.

‘China’s nuclear strategy probably includes consideration of a nuclear strike in response to a non-nuclear attack threatening the viability of China’s nuclear forces,’ the DIA warned, adding that ‘Beijing probably would also consider using its nuclear force if a conventional military defeat in Taiwan gravely threatened the regime’s survival.’

There are no higher stakes in geopolitics. It is reassuring, if only a little, to know that China and the US have engaged in a technical dialogue and that Xi intervened to persuade his ‘close friend’ President Vladimir Putin not to use a tactical nuclear weapon in the Ukraine war. It is also worth recalling President Donald Trump’s public musing on his desire to strike a grand disarmament bargain with the two powers.

Stillman and Reed would, no doubt, have shared some sharp views on the dramas of 2025. They saw radical Islam as the foe and wrote that China had covertly helped Iran since 1991 with uranium supply and enrichment, as well as missile technology. I recall that Stillman did not hesitate to use the cold-blooded tones of Dr Strangelove.

It is, however, valuable to restate their thoughtful conclusion that a unified effort is needed for the painstaking work of peaceful coexistence: ‘finding the fissionable materials, strengthening the International Atomic Energy Agency (IAEA), getting realistic about energy policy, rebuilding the American intelligence community and taking China seriously’.

Finally, let us memorise the judgement of these two departed Cold Warriors on the temptation of a quick fix. They wrote: ‘the destruction of fissile-material-production facilities by an act of war is not a cure; it is only a treatment, like dialysis or chemotherapy. Such attacks would have to be repeated every decade, as the victim’s bitterness grows’.