Klaus Fuchs is arguably one of the most notorious spies of the early Cold War period, betraying not only American atomic secrets between 1941 and 1950 but British ones as well. From 1943 to 1946, Fuchs worked for a time at Los Alamos, New Mexico, one of the sites of the top-secret American Manhattan Project during the Second World War. In Britain, before and after Los Alamos, he worked on the British nuclear project. Several books on Fuchs and the way his treason came about have been written over the years.¹ This 2020 book by Frank Close is not only meticulously researched, lively, and well written, it has the added benefit of making ample use of archive material that has become available over the last few years, especially from British archives. A fair amount of material on the Fuchs case has been released by the British Security Service (MI5), but a major source for the book was also the so-called Vassiliev Notebooks (Wilson Centre Digital Archive, 2009). These were put together semi-clandestinely in Moscow in the mid-1990s by the former KGB officer Alexander Vassiliev on the basis of archive material of the Russian foreign intelligence service SVR, the successor organisation of the KGB First Chief Directorate.² The added value of the book lies in the fact that Close, a distinguished physicist in his own right, is well acquainted with the scientific and technical side of atomic fission and related topics. He manages to explain these issues in an accessible way, without getting too bogged down.The author also pays special attention to the fact that Fuchs not only betrayed his adopted country, Britain, but also its main ally. He betrayed the trust of close friends and academic colleagues as well, who often worked with him for years.³

The outlines of the Klaus Fuchs story are fairly well known. Fuchs was a communist activist in Germany in the early 1930s, as were some of his family members, several of whom would later become victims of the Nazi regime in one way or another. Fuchs fled the country shortly after the Nazis came to power and arrived in England in September 1933. After the outbreak of the war, he was interned for a while on the Isle of Man and in Canada. He was a brilliant scientist, and his expertise was much needed on the British atomic project. He was therefore released from internment and subsequently even acquired British citizenship. After his work for the British government, he went to the United States in 1943 and thus became a key figure in the American nuclear project at Los Alamos. There, he made a vital contribution to the development of the plutonium bomb, the first of which, code named Trinity, was tested in the desert of New Mexico in July 1945.

From an intelligence history point of view, there are many fascinating elements in Fuchs’ career as a Soviet agent, as Frank Close makes abundantly clear in this book. In Britain in August 1941, through an intermediary, Fuchs asked to be put in touch with a Soviet representative. That’s when he was signed up as an agent by the GRU, Soviet military intelligence, before he came to the United States in 1943. Fuchs had realised, of course, the importance of the research on the atomic bomb that he was working on in Britain. Sharing this with the Soviets would be, in his view, his own contribution to “the war against fascism.” Fuchs was, in other words, a walk-in, that is, an agent who is not actively recruited by an intelligence service but offers to supply it with secret information spontaneously and of his own free will. Some of the most valuable agents during the Cold War, both for the Soviet Union and the West, were walk-ins. Among other important aspects of the case was Fuchs’ motivation. He transmitted top secret information to the Russians not for financial reasons but out of ideological sympathy for the Soviet cause. He was a Communist, after all.

One of Fuchs’ GRU handlers in England before he came to the United States was the legendary “Sonya,” real name Ursula Kuczynski, but also known as Ruth Werner, Ursula Hamburger and Ursula Beurton. She was a German Communist, like Fuchs, and operated for Soviet military intelligence in Asia and in several European countries for about twenty years in the 1930s and 1940s (Macintyre, 2020). Interestingly, Fuchs was no longer handled by the GRU once he arrived in the United States in 1943. He was transferred to the NKVD, one of the forerunners of the KGB. Why this transfer took place is not entirely clear, but it could have to do with the fact that the GRU did not have the personnel with high-level scientific expertise available to handle an agent like Fuchs in the United States. Even the renowned Sonya, Fuchs’ last Soviet intelligence handler in Britain before 1943, had no real knowledge of nuclear research as far as is known.

In the United States, Fuchs had meetings with an American NKVD courier by the name of Harry Gold, who had a scientific background. Interestingly, during one his first meetings with Gold, Fuchs was asked for information on matters that he had already communicated to the GRU when still in Britain. There was a majoir hiccup in the transfer of the agent, as Close keenly notes, because Soviet military intelligence had not handed over to the NKVD all the material it had acquired from Fuchs.

After the meetings with Gold in the United States, the material Fuchs delivered was regularly handed over by the courier to Anatoly Yatskov, an NKVD officer stationed in New York who had an engineering background and specialised in technological and scientific espionage. In 1996, Yatskov was posthumously given the highest award “Hero of the Russian Federation” by the then president Boris Yeltsin, an interesting small fact that is not mentioned in this book.⁴ The awarding of this title can no doubt at least partly be seen as an indication of the importance of Fuchs as an agent in the eyes of the post-Soviet Kremlin.

The author offers a telling indication of the success of the intelligence operation with Fuchs, which was part of the larger effort by the NKVD to acquire information about the American atomic project, code named Enormoz (Enormous) by the Russians. The information about the upcoming testing of Trinity, mentioned above, including a range of key specifications of the bomb, was given to Harry Gold by Fuchs well ahead of the explosion in the desert of New Mexico. The encrypted information was sent from the Soviet Embassy in Washington DC to Moscow on 13 June 1945, slightly more than a month to the day before the actual test. It again makes clear, how, partly thanks to Klaus Fuchs,⁵ Moscow was very well informed about the American project.

Fuchs returned to Britain after the end of the war, in 1946, and went to work at the atomic research establishment at Harwell near Oxford. During this period, until his arrest in February 1950, he betrayed a further treasure trove of British atomic secrets to his Soviet masters, including information on the hydrogen bomb (H-bomb). In the meantime, it had become known to the Americans that Fuchs was in touch with Soviet intelligence when he was working on the Manhattan Project several years earlier. This was revealed by the Venona project that worked on decrypting Soviet intelligence messages sent from NKVD stations in the United States to Moscow in the 1940s.

The book Trinity aptly describes how the information regarding Fuchs that came from the Venona project was by necessity excluded from any court proceedings due to its top- secret nature. The British authorities were restricted to the evidence against Fuchs gathered independently from Venona. In the end, his conviction and sentence of fourteen-year imprisonment by a British judge mostly came about through his own confession and supporting evidence that he offered in bits and pieces, often after considerable prodding by his interrogators. If he hadn’t confessed, the author emphasises, Fuchs most likely would have remained a renowned scientist in Britain for the rest of his life and probably important awards would have come his way. As it was, he served nine years of his sentence, was released in 1959, and thereupon expelled from Britain. He had lost his British citizenship and spent the remainder of his life until his death in 1988 in the German Democratic Republic. Of course, if he had confessed to similar acts of treason in that country, there is no doubt that an East German court would have given him a death sentence.