Norman Moss - Klaus Fuchs - The Man Who Stole the Atom Bomb

Once, at Harwell, someone was chatting with Fuchs about Alan Nunn May, and he said he could not understand why Nunn May took some small sums of money from the Russians. Fuchs said he might have done so as a sign of his commitment to them. This idea stuck in his mind, and he did something he had not done before: he accepted £100 as a cash payment from his Soviet contact. This was too small a sum to be either a proper reward for his services or a real inducement to continue them. He took the money as an assurance of his commitment and his loyalty, after being out of contact for a time. For someone as independent as Fuchs, accepting the money was a gesture of humility, a bending of the knee.

He soon had an item of information to give to the Russians that was so secret that his Harwell colleagues did not know it. This was that Britain was building its own atomic bomb.

The decision was taken in January 1947 by Prime Minister Attlee and a small group of his Cabinet ministers. It was not a very controversial decision. Britain was then a world power, one of the big three that had won the war. It relied on itself for defence (NATO was two years in the future). Few people in Britain, or in America for that matter, doubted that Britain should have all the weapons that another big power had. None the less, Britain was going through a desperate time economically that winter, and there might have been criticism at the launching of this programme just then, so the decision was kept secret and not even the full cabinet was told. Work began under William (now Lord) Penney, who had been at Los Alamos for a while and was now the man in charge of all weapons research under the Ministry of Defence.

Few people at Harwell — perhaps no one — knew as much about atomic bombs as Fuchs, so he was assigned to do the theoretical work. It was decided very early on that it would be a plutonium bomb, and Fuchs’s knowledge of plutonium reactions and implosion technique, acquired at Los Alamos, was very valuable. When he and a few others at Harwell who were working on the project went to see Penney at the Ministry of Defence weapons establishment at Fort Halstead, Kent, they did not tell anyone else where they were going.

Fuchs put his best effort into this work. He argued with Penney against building the kind of bomb they could build most quickly in favour of going for a more sophisticated weapon with an eye on longer-term development. When he was providing information to Russia, he did everything he could to help Russia, but on those days when he was working on the atomic bomb for Britain, he was doing his best for the British bomb.

The existence of the bomb programme was not revealed until May 1948, and then only in answer to a formal question in Parliament. A Labour Member asked whether the Minister of Defence was satisfied with progress in developing the most modern weapons. The Minister, A. V. Alexander, replied: ‘Yes, sir. As was made clear in the Statement Relating to Defence, 1948, research and development continue to receive the highest priority in the defence field, and all kinds of weapons, including atomic weapons, are being developed.’ [13] As I have written elsewhere, that phrase ‘including atomic weapons’ must be one of the great throwaway lines of British history. — NM

Thanks to Fuchs, the Russians knew about the British bomb programme before some British Cabinet ministers. As the programme advanced, Fuchs gave them the figures of British plutonium production, which told them how many bombs Britain could produce, and gave them details of the plutonium reactor to be built at Windscale. He also told them some things that were left over from Los Alamos. He gave them more details of the construction of the plutonium bomb, and the problems caused by spontaneous fission in plutonium.

He made his own calculations of the power of the Hiroshima and Nagasaki bombs, and gave them the results of these. He also recounted the ideas going around Harwell for different kinds of reactors, including the fast breeder reactor, which he was particularly involved with. All this would be useful to Soviet scientists working in the area.

They were working in this area. After Hiroshima, Stalin had given orders to put the atomic bomb programme into high gear. The project became an empire, over which Igor Kurchatov ruled. Laboratories were expanded, factories to build fissionable materials were set up in sparsely inhabited areas beyond the Urals, and a new programme to explore for uranium was mounted. In later stages, uranium 235 diffusion was given less attention as the Soviet scientists decided to take the plutonium route to their first atomic bomb.

As before, Soviet scientists absorbed Fuchs’s information and sent back questions. The first postwar American atomic bomb test was staged at Bikini in September 1946, and he was asked about this, although he had no direct information to give them. He was also asked about American plutonium production, which related to how many atomic bombs America had. He could give them an idea of British production but not of American.

He was asked about the ‘tritium bomb’, which he assumed meant the super, for most ideas of a fusion explosive involved the use of tritium. He told them all he could about the thinking at Los Alamos before he left on how a super might work. He also gave them some relevant figures on the deuterium-tritium reactions, which may have been the same ones that he smuggled out of Los Alamos at Bretscher’s request to give to Chadwick. He said later that the question about tritium showed that the Russians had another source of information at Los Alamos. But Soviet scientists could have foreseen the possibility of a super, and could have foreseen that it would work with tritium, just as American scientists did.

There was a much stronger indication that the Russians had another source of information in the British atomic energy programme. Fuchs was asked about a specific report produced at the Chalk River, Ontario, reactor, which he had never seen or heard of. He was also told that there was a report on ‘mixing devices’ and was asked whether he could get it. He had not seen this, but he found it at Harwell and provided the Russians with extracts.

In the summer of 1950 another Harwell scientist, Bruno Pontecorvo, a naturalized Italian, went on holiday on the Continent and disappeared, to turn up later with his family in Moscow. It transpired that he had been a Communist in the past. His defection has always been a mystery; he may have been giving information to the Russians while he was at Harwell, but security authorities never found any evidence of it.

Just as Fuchs was doing his best to build a British bomb while he was betraying its secrets to Russia, so he always showed at Harwell an extreme concern for security even while he was breaching it so significantly. He was a stickler for the rules on security (so was Nunn May).

Once, he was leaving Harwell with Egon Bretscher and they were talking about an aspect of their work. As they passed through the gate on to a deserted country road, Fuchs said, ‘We’ll have to stop talking about it now.’

On another occasion, he wrote to a colleague sternly: ‘You may remember that last week I gave you a document on the understanding that it would be restricted to members of the Technical Committee and Sir John Anderson’s committee. In the meantime, I have seen this document in other hands; no harm has been done in this instance, and I don’t intend to follow it up. However, it does raise the question whether at present there is any machinery to ensure that such restrictions are observed.’

One other instance of this concern is notable. Professor R. V. Gurney, who had been a senior member of the physics department at Bristol University when Fuchs was a research assistant there, was considered at one time for a post at Harwell. Fuchs advised that there might be a security problem because Gurney and his wife held strong pro-Soviet views; they had attended meetings in Bristol, along with him, of the Society for Cultural Relations with the Soviet Union, although he did not mention this.