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Emil Julius Klaus Fuchs

On 24 September 1933 Klaus Fuchs crossed the English Channel by ferry, and landed at Folkestone with the intention of studying at Bristol University. He was allowed to enter the United Kingdom on condition that he immediately registered with the police, and he ‘proceeded to the residence of Mr Gunn’, near Bristol, ‘a friend of his father’. The immigration officer’s report commented: ‘[Bristol University] had no facilities for the particular branch of applied mathematics which Fuchs wishes to study, but offered alternatives. Fuchs said that he proposed taking one of these alternatives: Physics.’ He was allowed to immigrate as he ‘was of good class’.

Somehow Fuchs made his way from Folkestone, on the east coast, 150 miles to Clapton-in-Gordano, near Bristol in the west of England, where he settled as the guest of Ronald and Jessie Gunn. Ronald Gunn was about ten years older than Fuchs, ‘very tall’ and ‘angular’ in appearance. An accountant, he was also a director of the Imperial Tobacco Company in Bristol and a cousin of fellow director Henry Hubert Wills, whose largesse funded the H. H. Wills Physics Laboratory at Bristol University. The Gunns too were well off, and lived in a large house with a ‘staff of servants’.

Fuchs then enrolled as a student of physics at the University of Bristol. He had studied at Leipzig and Kiel, of course, but never formally graduated; with this background already in place, in Bristol he registered for ‘B.Sc. by research’. He felt no need to hide his political beliefs, and almost immediately it became apparent that he was well connected to socialists on the continent. At a meeting of the university’s Socialist Society in February 1934, for example, Fuchs produced a message that had come from a contact. The name of his informant was not revealed but on the basis of what he had received Fuchs told the gathering that Georgi Dimitrov, who had been charged with arson for setting the Reichstag on fire, would be released or executed within days. Fuchs’ prediction was dramatically confirmed when, about three days later, Dimitrov was indeed released. The meeting was reported in the News Chronicle but seems to have attracted no special attention at the time. Dimitrov, we now know, was head of the Comintern in Western Europe.

Ronald Gunn became Klaus Fuchs’ rock in an alien land. Gunn’s liberal socialist beliefs matched those of the young scientist. Gunn had visited the Soviet Union in 1932, and would do so again during Fuchs’ tenure; He was the founder and first chairman of the Bristol branch of the British Commonwealth Cultural Relations Society and the Soviet Socialist Republics Union.. Its members included ‘several of the [university] physics staff’, and one Erna Skinner, wife of the Bristol physicist Herbert Skinner, of whom more later. The group met regularly, often at Miss Brownlee’s in Charlotte Street or at Gunn’s substantial house. This brought Gunn to the attention of the Security Services when the Chief Constable of Bristol alerted MI5’s head of investigations, Brigadier Harker, ‘foreigners regularly call at his house and they are made much of there’. What’s more, the police chief added, the local postman had noticed unusual items in the mail, including a package from Moscow and postcards referring to a ‘Left Book Club’. Investigations revealed that this book club – in reality the Cultural Society just mentioned – held meetings at the Gunns’ house, and at one of its gatherings there was a talk on Mein Kampf. This left the security authorities confused as to Gunn’s allegiances, which they described as ‘leaning towards either Communism or Nazism’.

All went well for Fuchs in England until 3 August 1934, when he asked for an extension of his passport. The German Embassy in London rejected the request because of Fuchs’ well-known political allegiance in Kiel, and said that he would have to apply in person at his home town in Germany.

Two months elapsed before Fuchs took action. On 6 October he sent a registered letter to the Municipal Offices in Kiel asking for a certificate from the Kiel police for issue of a new passport. Ten days later the police chief of Kiel told the German Consulate in Bristol that there were ‘political doubts against the issue of a passport to Fuchs’. On 23 October the consulate informed Fuchs that the issue of a new passport had been declined. Their London Embassy was prepared to issue a short-term certificate, however, which would ‘only enabl[e] the voyage back to Germany’.

Fuchs knew that the moment he stepped on to German soil he would be arrested. With no passport, and effectively stateless, his future lay in the hands of the British authorities. He received temporary respite when in July 1935 they allowed him to remain in the United Kingdom to complete his degree and to undertake research in Bristol under the guidance of Neville Mott. Mott, who as we have seen was a former colleague of Peierls at Cambridge, suggested that Fuchs apply the new quantum theory to understand the dynamics of metals and electrical conductors.

The university declared him ‘fitted to pursue research for Ph.D. or M.Sc.’ on 4 June 1935. The timing was fortunate because at the start of July the physics department hosted a major conference on the nature of metals. Fuchs is visible in the conference photo (see Plate 3), partly hidden in the back row. Luminaries at the conference include several destined to play roles in Fuchs’ career. Edward Teller, father of the American hydrogen bomb, sits cross-legged at the right (as we view the image) of the front row; seated on a chair at the right is Herbert Skinner, whose wife, Erna, would a decade later have an affair with Klaus Fuchs; four places to the left of Skinner sits the bespectacled Rudolf Peierls.

This would have been the first time that Fuchs came across Peierls, though as Fuchs was a novice it is unlikely that they had close contact. It was in the following year, 1936, that Fuchs wrote the physics paper which established him as an outstanding new talent and brought him to Peierls’ attention. A group at Bristol University had measured how easily an electric current can pass through conductors only a few atoms wide. The results disagreed utterly with the standard theory, which had been formulated by the discoverer of the electron itself, J. J. Thomson, three decades earlier. Fuchs investigated the reasons for the large discrepancy and found the culprit: in deriving his celebrated formula, Thomson had made a conceptual error.

We can visualize the phenomenon and get a sense of the error if we compare the current of electrons through a wire to the flow of water in a river or stream. Not all pieces of flotsam travel at the same speed: some go slightly faster or slower than the average. When the stream is very narrow, surface debris frequently hits the banks. Individual pieces of slow flotsam return to the main stream in a different pattern to faster elements. Fuchs realized that Thomson had taken the average of the range of speeds in a way that, while correct for a wide river, did not adequately allow for the different responses of fast or slow flotsam in a thin stream, where collisions with the banks play a more important role. Fuchs had found the flaw; now he had to correct it.

It was at this juncture that Rudolf Peierls visited Bristol at the invitation of Neville Mott for the seminar alluded to in chapter 1. While there, he learned of the anomalous experiment on electrical conduction in thin films, of Mott and Fuchs’ interest in it, and of Fuchs’ insight as to why Thomson’s theory was inadequate. Peierls listened to Fuchs’ explanation of Thomson’s error, understood the idea, and suggested how Fuchs might derive a mathematical formula to encapsulate it.

In the middle of the 1930s Mott and Peierls were among the founding fathers of quantum mechanics, in at the start with the first generation of theorists who had explored its mysterious promise. So fast had progress been that Fuchs, less than five years younger, was already of the next generation. He and his contemporaries were presented with the viable quantum theory, and applied it to an ever-increasing range of phenomena. It was Mott who had introduced the tools of the trade to Fuchs, pointed him to potential applications, and guided him through his first exploration. By 1936 Mott and Peierls were already maestros; Fuchs was an outstanding pupil.

Peierls analysed the puzzle after their discussion and informed Mott on 20 November that he had found a theoretical description of the conductivity problem. He was impressed two weeks later when he heard back from Mott that Fuchs ‘can get your answer by a more elementary method’. Mott suggested that Fuchs, Mott and Peierls ‘in alphabetical order’ should write a paper, but Peierls judged that Fuchs’ method was neater than his own, and that Fuchs should take the full credit: ‘I see no reason why my name should be added to Fuchs’ paper: all I did was to obtain the same result by a more complicated method.’

Fuchs duly wrote a paper, published in January 1938 under his name as sole author, in which he fulsomely acknowledged Peierls. Fuchs’ formula both explained the Bristol data and also showed how the ‘bounce’ of electrons from the surface (the ‘banks’ of the stream) varies if the surface is smooth or lumpy. Today this breakthrough is still used in microelectronics. First you measure the electrical resistance of a thin film when different amounts of current flow. Then, using Fuchs’ mathematical analysis, the results are translated to deduce the roughness – at the atomic scale – of the surface of a thin film. His paper has been acknowledged as seminal in over one thousand subsequent scientific papers; in other words, it has been referenced, on average, every month for more than eighty years. It is now cited more often than the basic work of Otto Hahn and Fritz Strassmann on nuclear fission.

Fuchs did more than physics in Bristol, however. He also kept up his political interests by making contact with Jürgen Kuczynski, the leader of the German Communist Party (KPD) in Britain. Kuczynski, based in London, was active in the Society for Cultural Relations between the Peoples of the British Commonwealth and the Union of the Soviet Socialist Republics, and it was probably during his visit to the Bristol caucus in 1937 or 1938, hosted by Ronald Gunn, that he met Klaus Fuchs for the first time.

Fuchs’ Bristol University colleague Herbert Skinner remembered him at this time as ‘an uncouth and callow youth’, who ‘never made friends with anyone in the laboratory and quite obviously lived in left-wing circles’. It is not clear, however, to what extent Skinner’s description has been coloured by his wife’s membership of those very circles, and her subsequent relationship with Fuchs. If reliable, this picture of him as withdrawn and closeted hints at the beginning of a change in Klaus Fuchs’ persona. His success as a political activist in Kiel suggests he had been a charismatic speaker, able to excite his fellow students. The English Klaus Fuchs was different. With as yet limited command of English, he protected himself carefully by keeping quiet. Only when in company with those with whom he felt confident would he open up. So was born the Klaus Fuchs whom Genia Peierls would later refer to as ‘penny in the slot’.

In 1936 the Spanish Civil War broke out, and it soon became an issue for intellectuals. At Bristol University this was true no less than on campuses throughout Europe and the United States. Fascist Italy and Nazi Germany supported General Franco’s Nationalists, whereas the Communist Party aided the Spanish Republicans. Many saw the war as the frontier in a fight for the survival of culture in the face of fascist tyranny. In this climate the Soviet Union became the champion of decency; Stalin’s genocidal purges and mass deportations to the Gulag were yet to be widely known. In the fight against fascism many intellectuals chose to follow the red banner of the Communist Party, as camp followers if not full members. Klaus Fuchs, while deeply sympathetic to the cause, as manifested in his membership of the Society for Cultural Relations between the Peoples of the British Commonwealth and the Union of the Soviet Socialist Republics, kept his communist beliefs largely to himself, however. His ties with Nazi Germany were certainly cut, as he ignored a letter from the German Consulate in Bristol reminding him that – as a German national – he was required to register for military service.

That same year Kristel managed to leave Germany to enter Swarthmore College, Pennsylvania, in the United States. She travelled via England and was reunited with Klaus. Any joy at this meeting, the first time that brother and sister had been together in three years, was soured by her news that the Gestapo had got wind that Emil, together with Gerhard, Elizabeth and their spouses, were smuggling Jews and socialists out of Germany. Klaus learned that Gerhard and his wife had spent two years in prison, but were now released. Kristel told Klaus that Elizabeth and Gustav had also been arrested. Elizabeth, who had subsequently been released, was now living with their father, Emil, in Kiel, but Gustav was in a concentration camp. At this juncture, Fuchs’ life-story looked similar to those of many others in his situation: a chronic fear for family trapped in Hitler’s dictatorship while maintaining anonymity for oneself in the shadowy world of German refugees and communist sympathizers in Britain. Lost in the canvas of a looming war, his tale would never have merited special attention. The course of Klaus Fuchs’ life, however, would be determined by his meeting with Rudolf Peierls. Their lives would become entwined, like father and son in a Greek tragedy.

The Story of Klaus Fuchs and Guy Liddell