In the meantime, there were some loose ends left over from the wartime collaboration. One of these concerned the question of how much information should be released to the public. Immediately after the end of the war a British-American committee was set up to decide what should be declassified. Fuchs was one of the British members.
The Americans came to Britain for a declassification conference and then, in November 1947, there was another meeting in Washington, and Fuchs went over there. He took a conservative line throughout, always on the side of keeping things classified; at times the line-up among the eight scientists was seven against one. (Another participant in that conference was the First Secretary at the British Embassy in Washington who dealt with atomic energy matters, Donald Maclean. Four years later, Maclean was to flee to Moscow with Guy Burgess, another Foreign Office man. These two, along with Kim Philby of the British intelligence service, had been recruited by the KGB when they were undergraduates at Cambridge in the 1930s.)
The Washington meeting lasted three days. After it was over Fuchs took up the threads of a number of friendships he had made at Los Alamos, on what must have been a very pleasant journey for him. He went to Cornell University in upstate New York and talked physics again with Hans Bethe and Richard Feynman. In Rochester he had dinner with Robert and Ruth Marshak, in whose home at Los Alamos he had spent a number of evenings. In Schenectady, he visited the General Electric laboratories, where the possibility of atomic power was being explored, and gave a lecture to some of the staff there, and then spent an evening with the Placzeks.
He went to the Argonne National Laboratory in Chicago, a visit arranged in advance that was not to take in any classified material, because this was the post-McMahon Bill era. He had Thanksgiving Day dinner in Chicago with Edward Teller and his wife, Mici. Then he went to Cambridge, Massachusetts, to see his sister Kristel and her family. At Cambridge he also saw old Los Alamos friends who were now at MIT, Victor and Ellen Weisskopf and Martin and Suzanne Deutsch.
He came back to England with a present for Mrs Peierls. It was a book, I Chose Freedom by Victor Kravchenko, a Soviet official who had defected, an anti-Communist autobiography that was then high on the American best-seller list.
He returned to a welcome event. His father Emil was coming to visit him, and stay over the Christmas season.
Mrs Alexander found a room for him in Lacie’s Court, and Fuchs introduced him to everyone at Harwell. Emil was proud of his son, and he showed it.
Emil, a small, tubby, rosy-cheeked man now in his seventies, was much more outgoing and talkative than his son. Unlike Klaus, Emil talked to others about his experiences in Germany and, in his case, the years of living under Nazi rule. He told Joy Alexander, when they were talking one evening: ‘You learn to live with the fear of the Gestapo knocking at the door.’
Fuchs, in all his talks with his father, never broached the subject of politics. He did not tell him whether he had changed his views since he left Germany as a Communist, and Emil, recalling the family agreement in the Germany of 1932 that they would not tell each other anything about their politics, did not ask him. He thought that if Fuchs wanted to tell him how his thinking had developed, he would do so. He did not seem to be engaged in any political activity.
The Skinners invited Fuchs and his father to a New Year’s Eve party, and they went. At this party, someone mentioned a newspaper story about a possible leak of information from Harwell. Fuchs, so quiet and buttoned-up, was an easy target for teasing, and Mrs Mary Buneman said in his presence, mischievously: ‘I think it’s Klaus. Why don’t you stop telling secrets to the Russians, Klaus?’ He smiled and just said, ‘Why should I?’ He must have known there was nothing serious behind the remark, but he stopped dropping in on the Bunemans after this. She and her husband noticed this and wondered if they had done anything to offend him; neither of them recalled the New Year’s Eve incident.
Another incident arising out of the party worried Fuchs a little. Egon and Hannah Bretscher, who both came from Zürich, spent some time talking to Emil Fuchs in German, and they invited both the Fuchs to come to dinner; they said that talking English must be tiring for the old man and he might like to spend an evening talking German. Afterwards, they forgot about the original purpose of the invitation and asked also Harwell’s Security Officer, Henry Arnold, and his wife. They had mentioned previously to Arnold that they had taken a lot of photographs at Los Alamos and Arnold said he would like to see them, and they decided that Fuchs might be interested in seeing them also.
The dinner party was not easy. Hannah Bretscher was heavily pregnant with her fourth child and was not feeling well, and Fuchs was even more silent than usual, but Emil was his normal chatty self and the Arnolds were companionable as always. At one point Emil remarked that he was going to take some basic foodstuffs with him when he went back to Germany, because there was a shortage there of most of the necessities of life. Food was still rationed in Britain but Hannah Bretscher, with three children, found that she could get more margarine than she needed. She telephoned Fuchs a couple of days later and offered to let his father have some so that he could take it back with him. Fuchs refused the offer brusquely, so that she wondered whether she had said something that offended him at the dinner party. Almost certainly, Fuchs was worried by the presence at the same dinner table of his father and a security officer; he was afraid that his father might inadvertently mention his Communist past, the same fear he had expressed to Harry Gold at their last meeting in Santa Fe.
Although Fuchs was a bachelor, his seniority entitled him to one of the prefabs on the Harwell site, and he moved into one when it became available in the spring of 1949. The address was 17 Hillside. He lived a bachelor’s life. He had a cleaning woman come in several times a week, although he kept his things tidy. In those days, shopping for food did not involve much choice: one took one’s ration book around the shops and bought one’s weekly ration of butter, bacon, and so on. A near neighbour, Mrs Marjorie Rennie, the wife of a mathematician in his division, used to take Fuchs’s ration books and do his weekly shopping for him. But he rarely cooked for himself, and usually ate dinner at Ridgeway Hall, where he ate his lunches. Once, several bachelors were discussing how to get their socks darned, for these were before the days of man-made-fibre socks, and one of them said, ‘Klaus, what do you do with your socks when they get holes in them?" I wear them,’ he replied.
He had an old pre-war car, but then he bought an MG sports car from Herbert Skinner, an acquisition that many of the younger bachelors envied, and that did not seem to suit his personality.
Old friends from Los Alamos often came to Harwell, because it was one of the few world centres of nuclear physics, and Fuchs would entertain them. Edward Teller came in 1949 as a member of the US Advisory Committee on Reactor Safety. Fuchs said he would like to talk to him, and asked him back to his house. But when Teller came, Fuchs looked at him and said, ‘You look tired. Would you like to lie down for a while rather than talk?’ Teller admitted that he was tired and accepted the offer gratefully, reflecting on Fuchs’s thoughtfulness.
One visit in particular must have pleased Fuchs. Robert Oppenheimer came in September 1948, as a guest of Cockcroft. He was then the Director of the Institute for Advanced Study at Princeton, New Jersey, a haven for leading thinkers in many fields — Einstein was then its most famous resident. Oppenheimer had dinner with Fuchs at a restaurant in Abingdon, and he offered him a place at the Institute as a research fellow. Any scientist would have been gratified by such an invitation, but Fuchs declined the offer with thanks. He said, however, that in some ways he would have liked to come, because at Harwell he was so caught up in administrative work that he was falling behind in his physics.