This phase in the saga had begun in the summer of 1940 when Fuchs was interned as an enemy alien. Max Born, his colleague and professor at Edinburgh University, had written to the authorities on 29 May urging that Fuchs be released, and had solicited Peierls’ support. Peierls replied in July and apologized for not having answered earlier. He was at that time, of course, fully engaged with the implications of his work with Frisch, which had raised the spectre of the atomic bomb.
In this correspondence Born had also expressed his frustration at being unable to contribute to the war effort due to his German background. This is evident in Peierls’ enigmatic response:
I know exactly how you feel, and could very well understand what you wrote, in fact I was thinking just along the same lines. I am afraid I cannot make any suggestions as to any pieces of research that are likely to be of practical importance.
Here, ‘practical’ means applicable to the war effort. Born had shared Peierls’ disappointment at being sidelined as an enemy alien and was looking for ideas to develop that would make him indispensable in the fight against the Nazis.
Like many of his contemporaries, Born was aware of the fission of uranium and of Bohr’s insight that using U235 rather than U238 was key. Indeed, in 1939, when he and Fuchs were in Edinburgh, the pair had ‘discussed the possibility of exploiting the gigantic energy involved’. Furthermore Born had been at Cambridge before the war and heard the Hungarian physicist Leo Szilard talking about a chain reaction and the possibility of a nuclear explosion. Already Szilard feared that Hitler might develop this ‘super-weapon and thus conquer the world’. Born’s memory, thirty years later, was ‘I think I discussed this with Fuchs [in 1939] after my return from Cambridge. In any event Fuchs was much more expert than I was as he knew much more about nuclear physics.’ There may be an element of false memory here as Fuchs’ main work by then was not in nuclear physics, but like many of their colleagues Born and Fuchs would have been broadly aware of the potential for releasing vast amounts of energy from the atomic nucleus. Fission and the possibility of a chain reaction were sensational ideas, but not secret.
At most their interest was that of physics kibitzers who followed developments with interest: they did no meaningful research into the phenomenon. Born’s discussion with Fuchs in 1939 was probably no different from those between many other theoretical physicists in the aftermath of the discovery of fission: first, to marvel at the prodigious energies involved, and then wonder how they might be realized in practice by experiment and technology. That nuclear power could be of service to humanity was an obvious possibility; that a deliverable bomb was feasible, however, was far from clear – the surprise of Werner Heisenberg and his German colleagues in 1945 when they learned that the Allies had succeeded at what they had thought to be impossible is testament to the received wisdom absent Peierls and Frisch. Heisenberg and his team were, like Born and Fuchs, unaware that only a few kilograms of U235 would be needed. In July 1940 Peierls’ reply to Born’s enquiry meticulously protected this terrible secret.
Within the constraints of that secrecy, Peierls elaborated on his current work:
The problems I am interested in just now do not really offer much scope for theoretical work, it is mainly a question of getting somebody to do the experiments. In a general way, if anybody can think of a new and efficient way of separating the isotopes of heavy elements, that would no doubt be of importance for many purposes. But I really think that all possible methods have already been explored, for example in Urey’s article [‘Separation of Isotopes’] in the Physical Society reports.
Peierls interest in separating isotopes of ‘heavy’ elements and the importance of fission in the heaviest known element, uranium, would have made his strategic goal rather obvious. But it gave no indication of any progress – if anything, quite the opposite.
Although Peierls’ war work would turn out to be the most far-reaching long-term consequence of that letter, the main content concerned one of Born’s students, a Polish graduate named Wolfgang Hepner. Peierls’ interest in Hepner is relevant to understanding the context of the hiring of Fuchs. Hepner had studied quantum mechanics with its founder, Erwin Schrödinger, as well as with Born, and so was a strong prospect. Peierls was keen for Hepner to study for a Ph.D. in Birmingham and had been negotiating with the university for him to begin in October 1940. Unfortunately – as Peierls explained to Born – the authorities at the University of Birmingham ‘are just now very reluctant to accept any new foreign students’. In this period when fear of a fifth column was rife, xenophobia within the university was no different from that in the population at large. Peierls stopped going to faculty meetings after he heard negative remarks that ‘former enemy aliens’ were attending them.
Despite this, Peierls must have received approval, for by October Hepner was at Birmingham – but without any funds to support him. Faced now with a potentially destitute student on his hands, Peierls wrote to Born at the start of November and asked whether there was any possibility of Hepner moving back to Edinburgh! To sugar the pill, Peierls added that he had heard from Neville Mott that Fuchs was about to be released from internment and would soon be returning to the United Kingdom but was without a job. Peierls explained: ‘I am doing some consulting work for a Government Department at present and am trying to get some relief from teaching.’ Peierls asked Born whether Fuchs – already with a Ph.D. and some post-doctoral experience – would like to come to Birmingham as a temporary lecturer.
Born did not know when Fuchs would return to the United Kingdom, however. As a result of this uncertainty Peierls decided not to proceed with Fuchs and instead continued to pursue the case of Hepner with the university. He told the authorities that he proposed to employ Hepner as a ‘private part-time assistant in order to enable me to devote more time to consulting work of National importance’. He explained that Hepner would spend most of his time as a research student in the university, and that the teaching would be a private matter between the pair of them – Peierls paying Hepner ‘One pound, eight shillings and ten pence per week’ for this work. Peierls stressed to the university that he had made ‘exhaustive enquiries to get a suitable assistant of British nationality but was unsuccessful’.
The university approved Hepner’s appointment. This satisfied Peierls’ needs in the short term, but once Hepner graduated and took a full-time job Peierls would be back at square one. So with an eye to the future, and aware that Born had no funds in Edinburgh to maintain Fuchs, Peierls asked Born to keep him informed if Fuchs returned.
By 12 March 1941 Peierls must have learned that Fuchs was back in Edinburgh and that Born had not yet found a job for him because he wrote again to Born about Fuchs’ prospects. Born responded immediately. In a letter of 16 March Born confirmed that Fuchs was back from internment in Canada and added that he would be ‘very grateful if [you] could help [me] find a suitable post for [him]’. On 22 March Peierls replied that there was no chance of a regular staff position for Fuchs at Birmingham, but there might be an opening for a temporary lecturer, or alternatively a hybrid position, part-time as a lecturer and the rest as Peierls’ research assistant.
Peierls gave Born the background. Hepner was about to complete his Ph.D. and seemed likely to take a job in industry; his departure would create room for Fuchs in one of those positions. Peierls’ question to Born was whether he would judge that to be ‘sufficient advance on Fuch’s [sic] present situation to justify his leaving Edinburgh?’
Born was very positive and wrote of Fuchs in glowing terms. He regarded Fuchs as one of the most outstanding young theorists at that time, describing him as ‘extremely gifted, on quite a different level from all my other pupils at Edinburgh’. His pen portrait of Fuchs was ‘a very nice quiet fellow with sad eyes’, who was both ‘shy’ and ‘penniless’.
Nearly two months then elapsed before Peierls sent a written offer to be passed to Fuchs in May. The autobiographies of Peierls and of Born hint at conversations that took place off the record during this period. Peierls’ autobiography is not specific about dates but the implicit chronology is tantalizing. First, on 22 March, Peierls asked Born whether Fuchs was ‘willing to join us’. Peierls’ narrative explains that he has asked for official clearance, and was ‘at first’ instructed to say as little as possible, to which he had replied that this would be impractical. Peierls continues: ‘In due course he got a full clearance and he started work in May 1941.’
Recall that Born had probably deduced that Peierls was interested in nuclear physics – possibly even U235 – when Peierls mentioned ‘separating the isotopes of heavy elements’ back in July 1940. This conclusion is supported by Born’s own memoir, which reveals that, when Peierls’ cryptic letter with its offer of employment arrived on 10 May, Born and Fuchs ‘both knew what it meant’. Peierls had raised the prospect of Fuchs working at Birmingham back on 22 March. Although no formal offer was made until 10 May, it seems possible that Fuchs could have been aware of Peierls’ interest in uranium isotopes, if only implicitly, when he visited Jürgen Kuczynski in the middle of April.