Editing Klaus Fuchs (section)

==Second World War==
Fuchs applied to become a [[British subject]] in August 1939, but his application had not been processed before the [[Second World War]] broke out in Europe in September 1939. There was a classification system for [[enemy alien]]s, but Born provided Fuchs with a reference that said that he had been a member of the SPD from 1930 to 1932, and an anti-Nazi. There matters stood until June 1940, when the police arrived and took Fuchs into custody.  He was first interned on the [[Isle of Man]] and then, in July, he was sent to internment camps in Canada, first on the [[Plains of Abraham]] in [[Quebec City]] and later at a site near [[Sherbrooke, Quebec]]. During his internment in 1940, he continued to work and published four more papers with Born: ''The Mass Centre in Relativity'', ''Reciprocity, Part II: Scalar Wave Functions'', ''Reciprocity, Part III: Reciprocal Wave Functions'' and ''Reciprocity, Part IV: Spinor Wave Functions'', and one by himself, ''On the Statistical Method in Nuclear Theory''.<ref>{{cite web |url=http://www-history.mcs.st-andrews.ac.uk/Biographies/Fuchs_Klaus.html  |title=Emil Klaus Julius Fuchs |first1=J. J. |last1=O'Connor |first2=E. F. |last2=Robertson |date=July 2008 |access-date=17 May 2013 |publisher=University of St Andrews, Scotland}}</ref>
[[File:Poynting Physics building 3.jpg|thumb|left|Poynting Physics building at the [[University of Birmingham]] ]]

While interned in Quebec, he joined a communist discussion group led by [[Hans Kahle]].{{sfn|Moss|1987|pp=21–26}} Kahle was a KPD member who had fought in the [[Spanish Civil War]]. After fleeing to Britain with his family, Kahle had helped [[Jürgen Kuczynski]] organise the KPD in Britain.{{sfn|Williams|1987|pp=33–34}} Kristel arranged for mathematics professor [[Israel Halperin]], the brother-in-law of a friend of hers, [[Wendell H. Furry]], to send Fuchs some magazines, likely scientific journals. Max Born lobbied for his release. On Christmas Day 1940, Fuchs and Kahle were among the first group of internees to board a ship to return to Britain.{{sfn|Moss|1987|pp=21–26}}

Fuchs returned to Edinburgh in January, and resumed working for Born.{{sfn|Greenspan|2005|pp=238–239}} In May 1941, he was approached by [[Rudolf Peierls]] of the [[University of Birmingham]] to work on the "[[Tube Alloys]]" programme – the British atomic bomb research project. Despite wartime restrictions, he became a British subject on 31 July 1942 and signed an [[Official Secrets Act]] declaration form.{{sfn|Greenspan|2005|pp=238–239}}{{sfn|Moss|1987|p=43}}<ref>{{London Gazette |issue=35702 |date=11 September 1942 |page=3975}}</ref> As accommodation was scarce in wartime Birmingham, he stayed with Rudolf and Genia Peierls.{{sfn|Moss|1987|p=34}} Fuchs and Peierls did some important work together, which included a fundamental paper about isotope separation.{{sfn|Bernstein|2010|p=43}}

Soon after, Fuchs contacted Jürgen Kuczynski, who was now teaching at the [[London School of Economics]]. Kuczynski put him in contact with Simon Davidovitch Kremer (codename: "Alexander"; 1900-1991<ref>{{Cite web|url=https://www.yadvashem.org/research/research-projects/soldiers/simon-kremer.html |title= Simon Kremer}}</ref>), the secretary to the military attaché at the [[Soviet Union]]'s embassy, who worked for the [[Glavnoye Razvedyvatel'noye Upravleniye|GRU]] (Russian: ''Главное Разведывательное Управление''), the [[Red Army]]'s foreign military intelligence directorate. After three meetings, Fuchs was teamed up with a courier so he would not have to find excuses to travel to London. She was [[Ursula Kuczynski]] (codename: "Sonya"), the sister of Jürgen Kuczynski. She was a German communist, a major in Soviet Military Intelligence and an experienced agent who had worked with [[Richard Sorge]]'s spy ring in the Far East.{{sfn|Rhodes|1995|pp=51, 57, 63}}

In late 1943, Fuchs (codename: "Rest"; he became "Charles" in May 1944){{sfn|Laucht|2012|p=204}} transferred along with Peierls to [[Columbia University]], in New York City, to work on [[gaseous diffusion]] as a means of [[uranium enrichment]] for the [[Manhattan Project]].{{sfn|Moss|1987|pp=46–47}} Although Fuchs was "an asset" of GRU in Britain, his "control" was transferred to the [[NKGB]] (Russian: ''Народный Kомиссариат Государственной Безопасности''), the Soviet Union's civilian intelligence organisation, when he moved to New York. He spent Christmas 1943 with Kristel and her family in Cambridge.{{sfn|Rhodes|1995|pp=103–105}} He was contacted by [[Harry Gold]] (codename: "Raymond"), an NKGB agent in early 1944.{{sfn|Williams|1987|pp=70–73}}

[[File:Fuchs-klaus e.jpg|thumb|Fuchs's Los Alamos ID badge]]

From August 1944, Fuchs worked in the Theoretical Physics Division at the [[Los Alamos Laboratory]], under [[Hans Bethe]]. His chief area of expertise was the problem of imploding the fissionable core of the [[plutonium]] bomb. At one point, Fuchs did calculation work that [[Edward Teller]] had refused to do because of lack of interest.{{sfn|Rhodes|1995|pp=117–119}} He was the author of techniques (such as the still-used Fuchs-[[Lothar Wolfgang Nordheim|Nordheim]] method) for calculating the energy of a fissile assembly that goes highly [[prompt critical]],<ref>{{cite web |url=http://www.ansn.org/Common/documents/Training/TRIGA%20Reactors%20%28Safety%20and%20Technology%29/chapter1/characteristics33.htm |title=The Fuchs-Nordheim model and pulsing characteristics |publisher=[[IAEA]] |access-date=28 April 2013}}</ref> and his report on blast waves is still considered a classic.{{sfn|Szasz|1992|p=89}} Fuchs was one of the many Los Alamos scientists present at the [[Trinity test]] in July 1945.{{sfn|Rhodes|1995|p=175}}

Socially, Fuchs was later judged as someone who kept to himself, and never talked about politics. He was fairly well-liked. He dated grade school teachers Evelyn Kline and Jean Parker, and occasionally served as a [[babysitter]] for other scientists. He befriended [[Richard Feynman]]. Fuchs and Peierls were the only members of the British Mission to Los Alamos who owned cars, and Fuchs lent his [[Buick]] to Feynman so Feynman could visit his dying wife in a hospital in [[Albuquerque]].{{sfn|Szasz|1992|pp=35, 90–91}} When Fuchs was discovered to be a spy, his former colleagues were shocked. The postwar director of Los Alamos, [[Norris Bradbury]], later said that:

:Fuchs was a strange man. I knew him, though not well. A very popular, very reticent bachelor, who was welcome at parties because of his nice manners. He worked very hard; worked very hard for us, for this country. His trouble was that he worked very hard for Russia, too. Basically, he hated the Germans bitterly. He had an undying hatred and he simply thought this country was not working hard enough to assist the Russians to defeat the Germans. Well, he was in his own odd way loyal to the United States. He suffered from a double loyalty.<ref>{{cite book |last1=Bradbury |first1=Norris |editor1-last=Badash |editor1-first=Lawrence |editor2-last=Hirschfelder |editor2-first=Joseph O. |editor3-last=Broida |editor3-first=Herbert P.|title=Reminiscences of Los Alamos, 1943-1945 |date=1980 |publisher=D. Reidel |chapter=Los Alamos: The First 25 Years |page=167}}</ref>

Fuchs's main courier in the United States was [[Harry Gold]], a chemist who lived in [[Philadelphia]], but was willing to travel to wherever Fuchs was. [[Allen Weinstein]], the author of ''The Haunted Wood: Soviet Espionage in America'' (1999), has pointed out: "The NKVD had chosen Gold, an experienced group handler, as Fuchs's contact on the grounds that it was safer than having him meet directly with a Russian operative, but [[Semyon Semyonov]] was ultimately responsible for the Fuchs relationship."{{sfn|Weinstein|Vassiliev|1999|pp=186–187}}

Gold reported after his first meeting with Klaus Fuchs:
{{blockquote|He (Fuchs) obviously worked with our people before and he is fully aware of what he is doing. … He is a mathematical physicist … most likely a very brilliant man to have such a position at his age (he looks about 30). We took a long walk after dinner. … He is a member of a British mission to the U.S. working under the direct control of the U.S. Army. … The work involves mainly separating the isotopes... and is being done thusly: The electronic method has been developed at Berkeley, California, and is being carried out at a place known only as Camp Y. … Simultaneously, the diffusion method is being tried here in the East. … Should the diffusion method prove successful, it will be used as a preliminary step in the separation, with the final work being done by the electronic method. They hope to have the electronic method ready early in 1945 and the diffusion method in July 1945, but (Fuchs) says the latter estimate is optimistic. (Fuchs) says there is much being withheld from the British. Even [[Niels Bohr]], who is now in the country incognito as Nicholas Baker, has not been told everything.{{sfn|Trenear-Harvey|2011|pp=74–75}} }}

After the end of the war, in April 1946, he attended a conference at Los Alamos that discussed the possibility of a [[thermonuclear weapon]]; one month later, he filed a patent with [[John von Neumann]], describing a thermonuclear weapon design the two had collaborated on. Though it was not a viable design, it was the first instance of the idea of [[radiation implosion]] being part of a weapon design. Radiation implosion would later become a core part of the successful [[Teller–Ulam design]] for thermonuclear weapons, but its importance was not appreciated at the time.{{Sfn|Bernstein|2010|pp=43–46}} Bethe considered Fuchs "one of the most valuable men in my division" and "one of the best theoretical physicists we had."{{sfn|Szasz|1992|p=89}}