Klaus Fuchs

Title:                  Klaus Fuchs

Author:                Robert C. Williams

Williams, Robert C. (1987). Klaus Fuchs, Atom Spy. Cambridge, MA: Harvard University Press

LCCN:    87008672

UB271.R9 F838 1987


Date Updated:  October 29, 2015

My graduate-school training was in nuclear physics, and in intelligence, among other things, I was a nuclear weapons specialist. The more I learned about the Manhattan Project, efforts at secrecy, and its total penetration by Soviet agents, the more I was amazed. I didn’t think I could be more astounded, but when the VENONA decrypts were published I was flattened with amazement.

In this book Williams traces the path of the spy Klaus Fuchs from Nazi Germany to Britain, Canada, New Mexico, and East Germany, where he retired from nuclear physics and lived until his death in 1988. The aim of the book is to highlight Fuchs’ espionage activities for the Soviet Union and to show how his case touched off a barrage of arrests of other spies, including the Rosenbergs. In addition to explaining Fuchs’ background and personal beliefs, the author also shows how he was only a part of a much larger Soviet effort to penetrate and control British intelligence. The appendices contain the confessions of espionage by Fuchs and Harry Gold.

Klaus Emil Julius Fuchs (29 December 1911 – 28 January 1988) was a German theoretical physicist and atomic spy who in 1950 was convicted of supplying information from the American, British and Canadian atomic bomb research (the Manhattan Project) to the USSR during and shortly after World War II. While at the Los Alamos National Laboratory, Fuchs was responsible for many significant theoretical calculations relating to the first fission weapons and later, the early models of the hydrogen bomb, the first fusion weapon.

Fuchs was born in Rüsselsheim, Grand Duchy of Hesse, the third of four children to Lutheran pastor Emil Fuchs and his wife Else Wagner. Fuchs’ father was later a professor of theology at Leipzig University. He became an active Quaker, both in Germany, England, and in the United States. Fuchs’ grandmother, mother, and one sister eventually committed suicide, while his other sister was diagnosed as schizophrenic.

Fuchs attended both Leipzig University and Kiel University, and while at Kiel became active in politics. Young Fuchs joined the Social Democratic Party of Germany and, in 1932, the Communist Party of Germany. In 1933, after a violent encounter with the recently installed Nazis, he fled to France and was then able to use family connections to flee to Bristol, England. He earned his Ph.D. in physics from the University of Bristol in 1937, studying under Nevill Mott, and took a DSc at the University of Edinburgh while studying under Max Born. His paper on quantum mechanics, published in the Proceedings of the Royal Society in 1936, helped win him a teaching position at Edinburgh the following year.

At the outbreak of war, German citizens in Britain were interned. Fuchs was put into camps on the Isle of Man and later in Quebec, Canada, from June to December 1940. However, Professor Max Born intervened on Fuchs’ behalf. By early 1941, Fuchs had returned temporarily to Edinburgh. He was approached by Rudolf Peierls of the University of Birmingham to work on the “Tube Alloys” program – the British atomic bomb research project. Despite wartime restrictions, he was granted British citizenship in 1942 and signed an Official Secrets Act declaration form.

A London message from the GRU, the Red Army’s foreign military intelligence directorate, dated 10 August 1941, refers to the GRU reestablishing contact with Fuchs. His initial Soviet contact was known as “SONIA”. Her real name was Ruth Werner, a German communist and a major in Soviet Military Intelligence.

As Fuchs later testified, after Nazi Germany invaded the Soviet Union in 1941 he concluded that the Soviets had a right to know what the United Kingdom (and later the United States) were working on in secret. Hence he began transmitting military intelligence to the USSR, though the historical record is unclear about exactly when he started. Fuchs’s testimony confirms that he contacted a former friend in the Communist Party of Germany, who put him in touch with someone at the Soviet embassy in Britain. His code-name was REST.

In late 1943, Fuchs transferred along with Peierls to Columbia University, in New York City, to work on the Manhattan Project. Although Fuchs was “an asset” of GRU in Britain, his “control” was transferred to the NKGB when he moved to New York. From August 1944 Fuchs worked in the Theoretical Physics Division at Los Alamos, New Mexico, under Hans Bethe. His chief area of expertise was the problem of imploding the fissionable core of the plutonium bomb. At one point, Fuchs did calculation work that Edward Teller had refused to do because of lack of interest. He was the author of techniques (such as the still-used Fuchs-Nordheim method) for calculating the energy of a fissile assembly which goes highly prompt critical. Later, he also filed a patent with John von Neumann, describing a method to initiate fusion in a thermonuclear weapon with an implosion trigger. Fuchs was one of the many Los Alamos scientists present at the Trinity test.

From late 1947 to May 1949, Fuchs gave Alexander Feklisov, his case officer, the principal theoretical outline for creating a hydrogen bomb and the initial drafts for its development as the work progressed in England and America. Meeting with Feklisov six times, he provided the results of the test at Eniwetok atoll of uranium and plutonium bombs and the key data on U.S. production of U235 (uranium-235). By revealing that America was producing one hundred kilograms of U235and twenty kilograms of plutonium per month, Fuchs made it easy for Soviet scientists to calculate the number of atomic bombs the United States possessed.

Thus, because of Klaus Fuchs, leaders of the Soviet Union knew the United States was not prepared for a nuclear war at the end of the 1940s, or even in the early 1950s. The information Fuchs gave Soviet intelligence in 1948 coincided with Donald Maclean’s reports from Washington, D.C. It was obvious to Josef Stalin’s strategists that the United States did not have enough nuclear weapons to deal simultaneously with the Berlin blockade and the Communists’ victory in China.

Fuchs later testified that he passed detailed information on the project to the Soviet Union through a courier known as RAYMOND (later identified as Harry Gold) in 1945, and further information about the hydrogen bomb in 1946 and 1947. Fuchs attended a conference of the Combined Policy Committee (CPC) in 1947, a committee created to facilitate exchange of atomic secrets between the highest levels of government of the U.S., Great Britain and Canada; Donald Maclean, as British co-secretary of CPC, was also in attendance. In 1946 when Fuchs returned to England at the Harwell Atomic Energy Research Establishment as the first Head of the Theoretical Physics Division, he was confronted by intelligence officers as a result of the cracking of Soviet ciphers known as the VENONA project.

Under prolonged interrogation by MI5 officer William Skardon, Fuchs in January 1950 confessed that he was a spy. Fuchs told interrogators the KGB acquired an agent in Berkeley, California, who informed the Soviet Union about electromagnetic separation research of uranium-235 in 1942 or earlier. He was prosecuted by Sir Hartley Shawcross and was convicted on March 1, 1950. He was sentenced the next day to fourteen years in prison, the maximum possible for passing military secrets to a friendly nation. In the infancy of the Cold War, the Soviet Union was nonetheless still classed as an ally, “a friendly nation”. A week after his verdict, on 7 March, the Soviet Union issued a terse statement denying that Fuchs served as a Soviet spy. Fuchs’ statements to British and American intelligence agencies were used to implicate Harry Gold, a key witness in the trials of David Greenglass and Julius and Ethel Rosenberg in the USA.

As a result of Fuchs’ information, the first Soviet bomb closely resembled, even in its external shape, the U.S.-developed Fat Man bomb.

Hans Bethe is reported to have said that Klaus Fuchs was the only physicist he knew who truly changed history. Because of the manner in which the head of the Soviet project, Lavrenty Beria, used foreign intelligence (as a third-party check, rather than giving it directly to the scientists, as he did not trust the information by default) it is unknown whether Fuchs’s fission information had a substantial effect (and considering that the pace of the Soviet program was set primarily by the amount of uranium they could procure, it is hard for scholars to accurately judge how much time this saved the Soviets). Some former Soviet scientists said they were actually hampered by Fuchs’s data, because Beria insisted that their first bomb (“Joe 1”) should resemble the American plutonium bomb (“Fat Man”) as much as possible, even though the scientists had discovered a number of improvements and different designs for a more efficient weapon.

Whether the information Fuchs passed relating to the hydrogen bomb would have been useful is still somewhat in debate. Most scholars have agreed with the assessment made by Hans Bethe in 1952, which concluded that by the time Fuchs left the thermonuclear program—the summer of 1946—there was too little known about the mechanism of the hydrogen bomb for his information to be of any necessary use to the Soviet Union (the successful Teller-Ulam design was not discovered until 1951). s The mechanism for igniting a thermonuclear explosion was developed by Teller and presented to Oppenheimer who recognized it as “technically sweet.” It remains one of the most closely held secrets of American military secrets.

Soviet physicists later noted that they could see as well as the Americans eventually did that the early designs by Fuchs and Edward Teller were useless. However, later archival work by the Soviet physicist German Goncharov has suggested that while Fuchs’ early work (most of which is still classified in the United States, but copies of which were available to the Soviets) did not aid the Soviets in their effort towards the hydrogen bomb, it was actually far closer to the final correct solution than was recognized at the time, and indeed spurred Soviet research into useful problems which eventually resulted in the correct answer. Since most of Fuchs’ work on the bomb, including a 1946 patent on a particular model for the weapon, are still classified in the United States, it has been difficult for scholars to fully assess these conclusions. In any case, it seems clear that Fuchs could not have just given the Soviets the “secret” to the hydrogen bomb, since he did not himself actually know it.

Some comments by Roy Berkeley:[1]

Walk one block west on Euston Road. You can’t miss Euston Tower on the northwest corner of Euston Road and Hampstead Road. Here, until recently, one of MI5’s main computers kept track of the Watchers. And now walk north on Hampstead Road for a jaunt through the kind of London that only Londoners know. For the next eight or so blocks you’ll see a microcosm of British commercial and institutional life: a government surplus store, an overseas airways office, a “gents hairdressing”, a printer, a cafe, a convent school, a retail butcher, a hardware store named “Things-U-Need”, a temperance hospital, a bookmaker. You’ll pass high-rise housing on mean little patches of lawn, and you’ll cross the tracks leading to Euston Station. It is an interesting few blocks, culminating in the more conventional shopping area surrounding Mornington Crescent underground station. Klaus Fuchs was imprisoned by the British in 1950 for having given vital atomic secrets to the Soviets between 1942 and 1949. But he had occupied the most sensitive positions in atomic weapons research because someone in MI5 either had neglected to subject him to scrutiny or had shielded him from scrutiny. Fuchs, a known communist, was somehow able to work on the Manhattan Project (in the US) and at Harwell (in the UK), both of which were closed communities of the most trusted physicists the West could assemble. On his return from Los Alamos in 1946, Fuchs was to meet his new Soviet controller outside this tube station. The contact would carry a bundle of five books in one hand and a book by Bennett Cerf in the other. Fuchs would carry a copy :pf Life. Fuchs never appeared, later claiming he was suffering “doubts about Russian policy” in the postwar period. But he delivered atomic secrets to the Russians until 1949, using a pub in Putney and the Kew Gardens tube station as·his London meeting places.

Soviet case-officers favoured tube stations as meeting places. John Vassall (see Site 12 Dolphin Square) met his controller at Finchley Road station; Blake (see Site 84 All Souls’ Place) used Belsize Park station; Yuri Modin preferred Turnham Green and Ealing Common when Burgess hadn’t insisted on meeting in a Soho pub; Oleg Penkovsky (see Site 76 The Mount Royal Hotel) told his briefers that Washington was a difficult city for agents because it lacked a subway system. With all the comings and goings at a station, anyone tailing either party would be noticed. Elaborate recognition signals would keep sensitive material from being pressed into the hands of some bloke simply waiting for his train. The signals were comical—who would stand in a public place holding a tennis ball, or a leather belt and an orange? But the work was hardly comical; Fuchs, for example, damaged the West far more than the Rosenbergs did, and Soviet possession of nuclear weapons by 1949 may well have encouraged North Korea to invade South Korea in 1950.

Where did security fail in the Fuchs case? The British opened a file on him as early as 1933, according to Robert Chadwell Williams; author of Klaus Fuchs, Atom Spy; young Fuchs then belonged to the German communist party. Fuchs fled Germany immediately after the Reichstag fire and reached England later in 1933. He made no secret of his communist loyalties when he entered the University of Bristol, or later when he was interned briefly as an enemy alien, or later still when he wanted to emphasize his anti-Nazism before an aliens’ hearing board. Only after he began research on nuclear weapons did he encourage people to perceive him as apolitical.

By then, Fuchs had acquired impeccable credentials and important friends. He had done research in Edinburgh with Max Born. He had met Rudolf Peierls who (with Otto Frisch) was the first to calculate that an atomic bomb could be built; when Peierls began working o nuclear fission in 1941, MI5 approved his choice of Fuchs as hi assistant. And in 1943 when Peierls asked Fuchs to go with him to the Manhattan Project, MI5 told the FBI incorrectly that Fuchs had been fully investigated.

When Fuchs returned to England in 1946 to head the theoretical physics division at the Atomic Energy Research Establishment at Harwell, again MI5 seemed incurious. Nigel West tells us in an article in Intelligence Quarterly that an immediate investigation of Fuchs was recommended in 1947 after a routine review of his file. “For reasons that have never been properly explained,” writes West, MI5 “overlooked the matter”. West concedes that Roger Hollis was “economical with the truth” concerning this lapse. Chapman Pinche goes further, charging in Too Secret Too Long[2] that “the person most responsible for [Fuchs’} successive security clearances was Roger Hollis”.

Serious suspicion fell on Fuchs in 1949 when the FBI decyphered some wartime messages between Moscow and its US diplomatic missions; one message pointed to a British scientist as having supplied information on the atomic bomb project. At this discovery, the security officer at Harwell and a skilled interrogator from MI5 began quiet discussions with Fuchs. Within the month, a strangely calm Fuchs confessed to even greater transgressions than his interrogators had suspected. For four violations of the Official Secrets Act, he received the maximum sentence: 14 years. (Had Britain been at war with the USSR, he could have been hanged.) Kept secret at the one-day trial was the fact that Fuchs was working at Harwell on Britain’s atomic bomb—a project hidden equally from the British public and the American government. John Costello thinks it “plausible” that the authorities knew of Fuchs’ spying but accepted it because of his contribution to Britain’s nuclear effort. Were the British so desperate to join the nuclear club that they didn’t mind carrying the Soviets along with them?

Fuchs left prison after ten years. He could have stayed in Britain (even with his naturalization revoked) but he went instead to East Germany and became deputy director of that country’s Institute for Nuclear Research. The institute’s director later defected and testified to the immense assistance Fuchs had given the Soviets: in April, 1942, Fuchs supplied the crucial early news of Western efforts that prompted the Soviets to start their own atomic-fission laboratory; he later supplied the details that enabled the Soviets to produce their own weapons; he even calculated America’s production of atomic bombs immediately after the war.

After his release from prison and until his death 39 years later, this man who had said in his confession that he eventually “disapproved of a great many actions of the Russian Government and of the Communist Party” gave his working mind completely to the Soviets and became a mouthpiece for all their nuclear propaganda. He never travelled outside the Soviet bloc, presumably because he wasn’t trusted. I’m not surprised. Fuchs, unforgivably, had made possible the capture of David Greenglass and the Rosenbergs when he co-operated with the FBI and identified the courier Harry Gold. (The Soviets, of course, had slipped up by using the same cut-out for Fuchs and Greenglass.)

Fuchs was, I think, a distorted and stunted personality. Three family members had committedsuicide (his maternal grandmother, his mother, a sister). His father, a Lutheran clergyman, had become a Quaker and vehement pacifist. Fuchs himself exhibited a belief in the correctness of Marxism that was not very different from his father’s religious fanaticism: a belief that The Truth had been uniquely revealed to him and that it justified any kind of behaviour from him. Klaus Fuchs’ faith in communism may have wavered, over the years, even when he was serving his religion most obediently, but he seems to have suffered no lasting doubts from either the Hitler-Stalin Pact (which he accepted as a necessary expedient) or the Khrushchev revelations of 1956 (which he ignoreds in moving to East Germany). Was he a “selfless” man, “driven by a moral passion to do what is right” as Norman Moss describes him in Klaus Fuchs: The Man Who Stole the Atom Bomb[3]? I think not. Anyone who remained committed to the communists after 1956 could hardly claim the moral high ground. But Fuchs was not living in the real world. On his release from prison he said he bore the British no bitterness. By any sane reckoning, however, he had seriously harmed the British and grievously betrayed their trust and hospitality. This man was untroubled by sane reckoning.

It is popular to regard the American concern with Soviet espionage, especially in the early days of the Cold War, as a “witch hunt”, suggesting that America was obsessed by a figment of an imagination gone hysterical. There were no witches, of course. But there were Soviet agents, and in his time and in his trusted place Klaus Fuchs did much to serve the Soviet system, a system that despised its own subjects and sought by every means to extend its tyranny everywhere.

[1] See Berkeley, Roy (1994). A Spy’s London. London: Leo Cooper, p.

[2] Pincher, Chapman (1984). Too Secret, Too Long. New York: St. Martin’s Press

[3] Moss, Norman (1987). Klaus Fuchs, A Biography: The Man Who Stole the Atom Bomb. New York: St. Martins


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2 Responses to Klaus Fuchs

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