He liked children, and they usually took to him and to his quiet, kindly, undemanding manner. He would talk to them at parties, and he sometimes took both the Peierls children hiking for a day.
He became a well-liked member of the Los Alamos community, regarded as a thoroughly decent man, probably with an unhappy past that he was keeping to himself. ‘He’s such a nice person. What a pity he’s so low key,’ said Mary Argo, and this was a typical opinion.
He started to drink a lot at parties, and showily. He could go through most of a bottle of whisky or gin in an evening. He seemed proud of his control, as he was when he was climbing cliffs; only he knew how much he was controlling. The drink helped him to forget what he was doing behind the backs of these friends of his. He explained this years later, in a letter he wrote from prison:
‘It surprised me when I found that I could get drunk without any fears. I thought at the time that even then I could control myself, but I don’t think the explanation is correct. I think the truth is that under the influence of alcohol, the control disappeared, but not only the control but the need for it, the whole other compartment of my mind.’
Evidently, when he drank he was no longer a spy, no longer giving away the secrets that the others kept, but was a loyal and upright member of the Los Alamos scientific community, and a worker in the effort in which they were all engaged together, that and nothing more.
The British Government opened a laboratory to do work on atomic fission in Montreal, jointly with the Canadian Government. This was to be kept separate from the US-British effort, and the British scientists working in America remained there.
By the early part of 1945 there was no doubt that a uranium 235 fission bomb would work, but there were still uncertainties about a plutonium bomb and the implosion technique. It was decided that there would have to be a test explosion before one could be used militarily. Preparations went ahead for the test, which was to take place, in secret, out in the desert at a place ninety miles from Los Alamos called Alamogordo. (Because some people would see the flash on the horizon, even from Las Vegas, a cover story was prepared saying that an army ammunition dump had been blown up in an accident.) Much of the work was now moving out of the theoretical stage. Uranium 235 and plutonium were arriving at Los Alamos from Oak Ridge and Hanford, and the chemists and metallurgists could experiment with it. Fuchs joined the team preparing for the Alamogordo test, which was codenamed Trinity. Versatile as always, he was assigned to calculating the blast effects of the explosion.
By now, Allied forces were overrunning Germany and the war in Europe was moving bloodily to its conclusion. The original impetus that drove many of them — the fear that Germany would build an atomic bomb first — was vanishing. Yet the pace of work at Los Alamos did not slacken, nor did the sense of urgency diminish. For one thing, men were dying every day now in the Pacific war, and the aim was to shorten this war. But also they were carried along by the sheer momentum of the project, with excitement building up as completion approached, and it did not occur to them to question whether they should continue. (There was one exception. Josef Rotblat, a Polish physicist who had done important work for Tube Alloys at Liverpool University and come over with the British scientists, decided when it was clear that the Germans were not going to have an atomic bomb that he no longer wanted to help build so destructive a weapon, and he told Chadwick, as head of the British mission, that he wanted to resign. Chadwick said he could but he asked him not to discuss his views with anyone else, so he left quietly. He went into radiation medicine, and has campaigned since for reductions in nuclear armaments.)
Once, at the Weisskopfs’, when people were talking about international affairs, Peierls made a remark that was critical of something Russia was doing, and Fuchs said, ‘There is another side to it.’ This comment was remembered because it was so rare. Fuchs never joined in discussions about world affairs. This was not particularly noticed because he was often silent when everyone else was talking.
Several people remarked on the fact that one of America’s major allies in the war, Britain, was taking part in the project but the other, the Soviet Union, was excluded. Some said that the atomic bomb should be shared with the Russians, and not sharing it was disloyalty to an ally. Niels Bohr, a founding father of atomic physics (Otto Frisch was at Bohr’s institute in Copenhagen when he hit on the idea of nuclear fission), had now arrived in Los Alamos, and he was revered by physicists. He wanted to bring the Soviet Union in on the atom bomb project. He worried that keeping the secret from the Russians would sow suspicion, and he foresaw the nightmare of a competition between the former allies in building atomic bombs. With his habit of wandering about and engaging anyone in a rambling conversation about whatever was in his mind, he told others at Los Alamos about his views, as he was later to tell Roosevelt and then Churchill, to little effect.
The idea of sharing the atomic bomb with the Soviet Union was not so outlandish. A number of people in high places thought that keeping the project secret from Russia was certain to create suspicion, and would sow the seeds of future conflict. After Bohr put this view in Washington, Supreme Court Justice Felix Frankfurter urged Roosevelt to bring the Russians in on the bomb project, and the British ambassador in Washington and former Foreign Secretary, Lord Halifax, agreed with him. Even the postwar British Foreign Secretary, Ernest Bevin, a doughty Cold War warrior, believed at one stage after the bomb was dropped that America and Britain should give Russia information about it, and some in the American administration agreed with him. After all, it was said, Russia was bound to build a bomb anyway, and keeping its secrets from her, with all the suspicion and hostility that this would engender, would save only a few years.
While everyone at Los Alamos worked on preparations for the secret tests, Fuchs was making his own preparations, for his next meeting with Gold, working alone in his room. He was going to give Soviet scientists all the help he could. He wrote a full account of the construction of both bombs. Doing this at Los Alamos was much easier than writing the details from memory in his sister’s house in Cambridge, for he had papers to refer to and he could give precise figures. Besides, the design for the bomb was just about completed now, and much of what was only speculative before was certain now. He reported that the bomb would have a solid plutonium core, and also a small initiator made of polonium as a neutron source. He gave full details of the tamper, the casing that held the bomb together for a few microseconds while the chain reaction started, and even the names of the two explosives that were to be used in the implosion, although he admitted that these names meant nothing to him. He explained a method of calculating the efficiency of the bomb devised by Bethe and Feynman, and also the figure for the efficiency that they had arrived at. Finally, as an aid to the explanations, he drew a diagram of the bomb, giving the most important dimensions.
Harry Gold had difficulty getting time off from his job to make the trip west in June, but he negotiated it as part of his summer vacation. He went by train to Albuquerque and took a bus to Santa Fe. His appointment with Fuchs was at four o’clock but he arrived in the city early, and spent an hour looking round a historical museum. There, he got a street map, the same as the one that Fuchs had given him in Cambridge back in February, located Alameda Street and walked along it under the trees to the Castillo Street Bridge, which was the meeting place. Fuchs drove up at four o’clock precisely, and Gold got in the car. Fuchs drove across the river and parked in a cul-de-sac, and they talked for a while in the car.