On 22 June 1941, less than a month after Klaus Fuchs began working with Peierls, Germany invaded Russia. That evening, Prime Minister Winston Churchill spoke to the nation on the radio and said, ‘We shall give whatever help we can to Russia and the Russian people.’ A few weeks later a formal military alliance was signed between the United Kingdom and the Soviet Union. If Fuchs had needed permission to take action, that alliance and Churchill’s rhetoric would have been it. In any event, Soviet archives record that Fuchs remembered his ‘former [sic] acquaintance’ with Kremer – the Soviet intelligence officer – and decided to transmit what he knew about the atom bomb project to that ‘representative of Russia as part of the war against fascism’. At some point over the summer Fuchs contacted Jürgen Kuczynski and told him about his new role in nuclear research. Kuczynski passed on Fuchs’ message. The London chief of GRU (Soviet Military Intelligence), Ivan Sklyarov (code name BRION), was alerted. He in turn consulted the GRU Centre in Moscow, which instructed him to recruit Fuchs.
Fuchs and Kremer met in London on 8 August 1941, a date established by the GRU and KGB records and which belies Fuchs’ later claims that he began espionage only in 1942. A deciphered GRU message from London to Moscow Centre on 10 August (see note 2), which referred to Fuchs as a ‘former acquaintance’ of Kremer, confirms that they had met earlier, most probably at Kuczynski’s party in April. Before the GRU decided to recruit Fuchs as a source they would have had to satisfy themselves that he was legitimate and not MI5 bait. This would have taken some time, which suggests that Fuchs approached Kuczynski at the latest in July, and possibly even earlier – in which case the timing is pushed tantalizingly close to the time that the Soviet Union’s role in the war changed. Such a timetable fits naturally with the thesis that Fuchs took his initiative upon hearing Churchill’s broadcast, although he never advanced this defence later. In any event, it would appear that 8 August 1941 was the date when Fuchs was formally ‘signed on’ by the GRU with the code name OTTO, and that his decision to spy for the Soviet Union had preceded that.
Fuchs had become privy to official secrets in the spring, was passing them to the Soviet Union by the summer, yet he did not receive warning about the Official Secrets Act until 11 October. That summer he joined the exclusive club of insomniacs haunted by knowledge that an atomic bomb was both possible and indeed likely. There was a practical method to concentrate U235, the amount needed for a single bomb was small, and the contract had just been placed with Metropolitan Vickers to design a twenty-stage diffusion plant that was expected to be ready by the end of the year. Fuchs knew the data on which these conclusions relied.
By the time of Fuchs’ arrival in Birmingham, Peierls had elucidated the problems in nine papers. Fuchs would have learned from the start that when a neutron hits a lump of uranium, the results depend not just on whether the target is U238 or U235 but also on the neutron’s speed. You can liberate energy from natural uranium when the neutrons are slow because 1 in every 140 atoms contains U235. This can be the basis for a heat engine – in modern language a ‘reactor’ – but does not create an explosion. If the neutrons have high energy they can induce fission in U238, but the secondary neutrons liberated in these reactions do not have enough energy to induce further fissions in U238. They can, however, cause fission in U235 if by chance they happen upon one of these atypical isotopes. Unfortunately, these ‘fast’ secondary neutrons tend to be captured by U238 atoms and are lost to the fission engine, so even if the amount of U235 is larger than normal, some means of slowing the neutrons is needed in order to maintain a chain of fission reactions. Start with about 50 kilograms of pure U235, on the other hand, and according to Frisch and Peierls an explosion would in theory be possible, whatever the neutron’s speed.
By the summer of 1941 Peierls and his new assistant were deep into the theoretical physics of gaseous diffusion and the design of a practical enrichment plant. There were so many variables that the work was both time consuming and difficult. Peierls produced a series of papers on assembly problems, and on different designs with fanciful names such as ‘rabbit’, ‘cul-de-sac’ and ‘cascade of cascades’, chosen, no doubt, to give no clues to their content. Fuchs’ study of uranium enrichment, when the uranium is in a compound molecule, formed the basis of his first papers with Peierls.
This was the state of knowledge in the summer of 1941, and of Fuchs’ particular contribution to it. When Fuchs met Kremer in August, he handed him six sheets of data, the first transmission of many over the next seven years. Kremer showed Fuchs’ documents to Sklyarov, who had some scientific training. On 10 August Skylarov – BRION – radioed a message to the GRU Centre, which when decoded read:
Barch [Kremer] conducted a meeting with the German physicist, Klaus Fuchs, who reported he is in a special group in Birmingham University working on the theoretical aspects of creating a uranium bomb. The work is expected to take three months and then the results will be directed to Canada for production purposes. Assuming that at least one per cent of the atomic energy of uranium explosive is released, a ten kilograms bomb will be equal to 1000 tons of dynamite.
The six pages of notes were sent to Moscow by diplomatic pouch that same day, but the war delayed them, and they did not reach the GRU Centre until early September. Meanwhile, the radio message had excited Moscow, as on 11 August came the response: ‘To Brion: Take all measures for obtaining information about the uranium bomb. Director.’
The transfer of top-secret information from Fuchs to Kremer was the classic spycraft of novels. The pair would meet at a busy bus stop, and sit side by side on the bus. Fuchs would be carrying copies of his papers in an envelope, or wrapped in packing paper, and when he was ready to alight would leave these on the seat for Kremer, who remained on board. On one occasion they met on a quiet residential street after dark and cruised around the neighbourhood in a car.
Fuchs would claim later that initially his conscience allowed him only to communicate his own work on diffusion. Moscow’s reaction suggests this is untrue. Fuchs’ own work at this early stage primarily showed that the presence of multiple isotopes in gaseous compounds of uranium would not confound the goal of diffusion enriching U235. While this was clearly of some importance, in the grand scheme of things it was relatively trifling. The sensational debut of Fuchs’ material in Moscow must have relied on the context rather than this particular contribution. The Director of GRU, General Alexei Panfilov, was technically trained and rated Fuchs’ notes ‘very important’. His assessment was that they revealed the British to be researching a weapon that ‘would put humanity on the road to Hell’.
Such a response would have been unlikely if Fuchs’ notes consisted solely of his two months’ work on diffusion. Instead it suggests that Fuchs – or someone else – also transmitted the key to the entire project: the Frisch-Peierls Memorandum of May 1940 itself. Fuchs’ message to Kremer that ‘the work is expected to take three months’ was Peierls and Frisch’s original estimate. Moscow’s reaction that the British were researching a weapon that ‘would put humanity on the road to Hell’ is also a fair paraphrase of Peierls and Frisch’s conclusion.
One consequence of Fuchs’ initiative was that Moscow Centre instructed Skylarov to find out about ‘work on uranium in other British establishments, such as Metropolitan Vickers and Cambridge University.’ These institutions were mentioned in a MAUD scientific committee report, whose first draft was discussed by committee members on 2 July. During the summer, the MAUD committee reviewed the document, and although Peierls was not formally a member, he too was ‘fully consulted’.
Of the thirty-one university scientists actively engaged in MAUD work, five were at Birmingham University, namely Peierls and Fuchs, along with two chemists, and Mark Oliphant, who was also on the MAUD committee. Peierls was fully aware of the project’s status, as outlined in the draft MAUD report, and Fuchs probably knew the preliminary report’s content when he met Kremer on 8 August; it might even have been his reason for doing so. When the final version arrived in Whitehall, on 27 August, the British civil servant John Cairncross passed a copy to his own Soviet handler. So by the start of September 1941, Fuchs and Cairncross had alerted the Soviet Union to this top-secret development.
Meanwhile, on 4 July 1941, G. P. Thomson, the chairman of the MAUD committee, learned that the Germans were trying to obtain heavy water. He urged Frederick Lindemann, Churchill’s science advisor and newly ennobled as Lord Cherwell, to develop a scientific intelligence programme to evaluate German progress. As this was too specialized to be an activity suitable for MI6, Thomson recommended that this needed ‘someone with knowledge of physics and especially of the personalities and specialities of German physicists’. The chosen intelligence gatherers were Peierls and Fuchs. What Thomson and Cherwell did not know was that while Fuchs was analysing German work on behalf of the British, he was already leaking the fruits of British work to the Russians.
In September he and Peierls visited London to ‘obtain copies of German scientific periodicals from MI6 and to deduce the location, travel, and research activity of German nuclear scientists’. The pair wrote a report, which concluded that German scientists were fully aware of the importance of separating isotopes to produce the fissionable U235. Peierls and Fuchs judged the centres of German basic research to be Heidelberg and Munich, in addition to Berlin. When MI6 asked ‘what steps were being taken to find out the movements of German scientists skilled in nuclear physics’, they were informed that Peierls and Fuchs were on the case. In reality Peierls was the main player as Fuchs had never been in German academic life long enough to know the background. Peierls showed Fuchs his findings, and consulted him on specific items. Their collaboration to assess German activity seems to have been between master and assistant, as was consistent with their relative standing and experience. Fuchs produced his first solo contribution in March 1942 with an analysis of a German paper, which worryingly dealt with separation of isotopes. Was this a clue to a German military programme, or harmless? He wrote to Perrin on 4 April 1942 and agreed with him that although ‘the more harmless interpretation appears to me more plausible … the other one should not be neglected’. This typifies the difficulty in assessing the threat from German science, for while Peierls and Fuchs’ reports identified tantalizing work relevant to the development of an atomic weapon, they produced no conclusive evidence that Germany had a significant active programme to that end. As Peierls summarized for Perrin on 29 August 1942: ‘We unearthed no very startling information, [but] there are some points of interest.’