The great betrayer

When Klaus Fuchs started passing atomic secrets to the KGB, he changed the course of world events. Forget about Philby and the Cambridge Five, that preening group of loudmouths that still dominate our national history of Soviet treachery. In his own quiet, devastating way, Fuchs proved more significant than all of them put together.

A brilliant but unassuming German refugee who found sanctuary in Britain, Fuchs rose to become one of the leading theoretical physicists of the Allied nuclear bomb project. As Frank Close, himself an Oxford nuclear physicist, writes: ‘By 1946, Fuchs knew more about the construction of the atomic bomb and the conception of the hydrogen bomb than anyone in the UK and all but a handful in the world.’ And because Fuchs knew it, his KGB handlers knew it too. Judging by this engrossing, brilliantly researched book, they knew it all.

Born in 1911 in Germany, Fuchs was a gifted, socially reticent man. At the University of Leipzig he studied science and mathematics, in which he excelled. He also inherited his father’s socialist leanings, and his political activism brought him to the attention of the Gestapo, which had him down on file as a communist. Fuchs fled the country in 1933, ending up at the University of Birmingham under the wing of Rudolf Peierls, one of the world’s leading theoretical nuclear physicists. Fuchs’s career flourished and as it did so, his work became highly sensitive. Peierls had been one of the first people to realise that nuclear fission could be used as the basis for a weapon of unimaginable power.

It was around this time that Fuchs first started passing secrets to the Soviets. The precise moment when he turned is a matter of conjecture — and that ambiguity is of deep significance. Until June 1941, the Soviet Union was allied with Hitler, and Fuchs always maintained that he began spying only after that point. But Close suggests that he offered his services to Moscow even while it was still aligned with Nazi Germany.

What secrets did he betray? The first and perhaps greatest challenge in making an atom bomb is in manufacturing the fuel. The necessary isotope of uranium is fiendishly hard to create. But Fuchs knew all the latest science on uranium, as well as how it could be used to manufacture plutonium, another type of bomb fuel. And when the combined Allied atomic weapons effort moved to the US, Fuchs went with it. This put him among the most knowledgeable nuclear scientists in the world and everything he learned and saw went back to Moscow, pages and pages of it, passed via KGB contacts in New York.

Fuchs then worked at Los Alamos, home of the Manhattan Project, where the bomb itself was assembled. On 16 July 1945, the first ever nuclear weapon was detonated in the wastes of America’s south-western deserts. The test, code-named ‘Trinity’, gives the title of this book. Then came Hiroshima and Nagasaki.

After the war, Fuchs returned to the UK to work at Harwell, the centre of Britain’s post-war atomic weapons programme. But the turning point came in 1949, with news that the Soviet Union had carried out its first nuclear test. This was a profound shock, as Moscow’s bomb programme was thought to have been in its infancy. But that assessment hadn’t reckoned on Fuchs’s treachery.

The code-breakers got him eventually, even though the FBI did its best to claim the credit. GCHQ and its US counterpart had read Soviet cables referring to an agent who, it was eventually established, had to be Fuchs. MI5’s interrogators finally cornered him in 1950 and he confessed. As the USSR had been a wartime ally, he did not face capital punishment and was instead sentenced to 14 years. He was out after nine, after which he moved to East Germany.

The scale of Fuchs’s spying was astounding, as were its consequences. It’s Close’s judgment that the information he betrayed formed the basis of the Soviet atom bomb project. But despite the enormity of the betrayal, and the possibility that he passed secrets to Nazi-aligned Moscow, Close gives no explicit verdict on Fuchs.

This leaves an unanswered question, which hangs over the book: did Klaus Fuchs do wrong? His justification for disclosing nuclear secrets was that the science was too important to remain the sole property of one faction. His duplicity was a betrayal of his friends, especially of Peierls, and of the country that had welcomed him. But it also played a part in ensuring that the Cold War ended not in the nuclear fire but in stalemate. Does that justify his actions?

And that in turn leads to an even more unsettling question: if Fuchs had never spied and only one side had developed the atomic bomb, would that have increased its use? The answer to that question is one nuclear secret that will never be known.