If he was self-contained emotionally and intellectually, he was dependent in other ways. He had little social competence. Mrs Peierls used to tell him when and how to get his laundry done and when to change his suit, and she used to remind him to send Christmas cards. With her children away, she took naturally to this mothering role. She used to choose most of her husband’s clothes, and when she decided that he needed a new suit, she would take him around the shops. Now she did the same for Fuchs.
Meanwhile, the Maud Committee’s work was advancing rapidly. In July 1941 Sir George Thomson, the Committee’s chairman, wrote a report for the Cabinet’s Scientific Advisory Committee saying that on the basis of the work done so far, there seemed a good chance that a uranium fission bomb could be produced before the end of the war. As a result, a full programme to build an atomic bomb was authorized, with the deliberately misleading name Tube Alloys.
Britain and the United States had been exchanging information on scientific work with military potential since the outbreak of war, and this included information on atomic fission. The optimistic report of the Maud Committee was sent to America, where it was seen by the Uranium Committee. Previously, this committee had reported that it was doubtful that an atomic bomb could be produced in time to have any effect on the course of the war. After seeing the Maud Committee’s report, they thought again, and a new committee was set up under the National Academy of Sciences. This committee recommended that work begin.
Two American physicists, Harold Urey and G. B. Pegram, were sent to Britain to make their own report. They were given access to all the British work. They visited the centres and saw the scientists involved, including Peierls and Fuchs, and took back with them an enthusiastic account of British progress. President Roosevelt considered both these optimistic reports, and in the first week of December 1941 he gave the go-ahead for a new organization to set about building an atomic bomb. At the end of that week, the Japanese bombed Pearl Harbor, Germany declared war on the United States, and the war became World War II.
Peierls and Fuchs were working on two tasks. One was doing theoretical calculations of nuclear fission reactions, which would show among other things how much uranium 235 would be needed for a bomb. The other was working out how to isolate uranium 235, for it was already becoming clear that this would be a major problem. The separation of isotopes is always difficult, because there is no chemical difference between them. The less difference there is in atomic number, and therefore weight, the more difficult it is to separate them. It is usually easy to distinguish between two objects if one is twice the weight of the other, as deuterium, an isotope of hydrogen, is twice the weight of ordinary hydrogen; it is much more difficult if the difference is only three parts in 238, as is the difference between uranium 235 and 238. It is easier to separate basketballs from tennis balls than basketballs from another kind of basketball that is fractionally heavier.
The separation method suggested in the Frisch-Peierls Memorandum, involving a heat transfer process, proved not to be viable. The favoured method was now a process of diffusion: the uranium would be turned into a gas and passed through membranes, so that more of the heavier atoms would be left behind and the lighter ones passed through. A pilot plant to try out this method was built at Valley, in North Wales, and scientists there got a taste of the horrendous problems involved in the process. The membranes had to be finer than any ever constructed before: the first specifications were for membranes one-thousandth of an inch thick perforated with holes one-ten-thousandth of an inch in diameter. Furthermore the gas, uranium hexafluoride, turned out to be very corrosive. Fuchs visited the plant, and saw the translation of his calculations into physical reality.
Peierls had every reason to be pleased with his choice of assistant. Fuchs was an excellent mathematician, and also he showed just the flexibility that Peierls had hoped for. Confronted with a new problem, he was quick to grasp the essentials. A Tube Alloys directorate was set up with a small office in London, and scientists working on different aspects of the project were required to send in monthly reports on their work. Fuchs always got his reports in on time, unlike many of the others; they were lucid — he wrote English easily by now — and he showed the same ability to pick out essentials.
At about this time, Peierls noticed a certain arrogance in Fuchs’s attitude. He always looked up to Peierls; however, when they went over papers they received from America on the work being done there, Peierls was ready to learn from them if there was anything new, but Fuchs’s attitude seemed to be, ‘Let’s see if the Americans are working on the right lines.’ Others, over the years, even at Bristol, remarked that although Fuchs was withdrawn, he never seemed unsure of himself. He had confidence in his own reasoning powers.
While the Maud Committee report was being prepared in the summer of 1941, something else of historic importance occurred. On 22 June, Germany attacked the Soviet Union. Instantly, the world situation was transformed. Russia was no longer a partner with Germany in a nonaggression pact, but was fighting for its life against it. Communist parties around the world threw their weight behind the war against Germany. They did so with a will. Communists had accepted that the Nazi-Soviet pact was tactically correct, as Fuchs did, but it left a bad taste in the mouth; Nazism and its values were hateful to them. Now Nazi Germany was the enemy once again and things were in their proper place.
Fuchs knew that the project he was working on was potentially of great military significance. Perhaps he would have acted as he did if Germany had not invaded the Soviet Union, but Russia’s plight must have given him added impetus.
He took a momentous step. It was probably less momentous for him than it would be for most people. In his searching eight-page confession, in which he analysed his motives, he devoted just one sentence to it: ‘When I learned the purpose of the work, I decided to inform Russia and I established contact through another member of the Communist Party.’ (The phrase ‘another member’ is interesting, for it indicates that he considered himself at that time still a member.)
Most of us have ties that might inhibit us from acting on strict political or even moral logic: ties created by background, environment, and family and other personal loyalties. We obey the law as a matter of habit. Setting out to give information to a foreign power would mean breaking out of the framework of laws and customs in which we live our lives.
But Fuchs had none of these ties, and there was no framework to break through. He had grown up in a German society in which the outlines were fluid, one that did not command the natural loyalty of all its citizens. Although he had applied for British citizenship, he did not seem to consider himself to be a part of British society. The flag of his native land was now the swastika, which he had every reason to hate. His only national commitment was to a Germany that did not yet exist, the post-Nazi Germany for which he had been told to prepare himself when he left Berlin. His only tie of loyalty was the one he had worked out in his own mind, to the abstraction of Communism; and because of this to a country that was, for him, hardly less abstract, the Soviet Union.