Klaus Fuchs Emil Julius Klaus Fuchs ( 29 December 1911 – 28 January 1988 ) was a German theoretical physicist and atomic spy who in 1950 was convicted of supplying information from the American , British and Canadian Manhattan Project to the Soviet Union during and shortly after the Second World War . While at the Los Alamos National Laboratory , Fuchs was responsible for many significant theoretical calculations relating to the first nuclear weapons and later the early models of the hydrogen bomb . The son of a Lutheran pastor , Fuchs attended the University of Leipzig , where his father was a professor of theology , and became involved in student politics , joining the student branch of the Social Democratic Party of Germany ( SPD ) , and the " Reichsbanner Schwarz - Rot - Gold " , the SPD ' s paramilitary organisation . He was expelled from the SPD in 1932 , and joined the Communist Party of Germany ( KPD ) . He went into hiding after the Reichstag fire , and fled to England , where he received his PhD from the University of Bristol under the supervision of Nevill Mott , and his DSc from the University of Edinburgh , where he worked as an assistant to Max Born . After the Second World War broke out in Europe , he was interned on the Isle of Man , and later in Canada . After he returned to Britain in 1941 , he became an assistant to Rudolf Peierls , working on " Tube Alloys " – the British atomic bomb project . He began passing information on the project to the Soviet Union through Ruth Kuczynski , codenamed " Sonia " , a German communist and a major in Soviet Military Intelligence who had worked with Richard Sorge ' s spy ring in the Far East . In 1943 , Fuchs and Peierls went to Columbia University , in New York City , to work on the Manhattan Project . In August 1944 Fuchs joined the Theoretical Physics Division at the Los Alamos Laboratory , working under Hans Bethe . His chief area of expertise was the problem of imploding , necessary for the development of the plutonium bomb . After the war he worked at the Atomic Energy Research Establishment at Harwell as the head of the Theoretical Physics Division . In January 1950 , Fuchs confessed that he was a spy . He was sentenced to fourteen years ' imprisonment and stripped of his British citizenship . He was released in 1959 , after serving nine years and emigrated to the German Democratic Republic ( East Germany ) , where he was elected to the Academy of Sciences and the SED central committee . He was later appointed deputy director of the Institute for Nuclear Research in Rossendorf , where he served until he retired in 1979 . Early life . Emil Julius Klaus Fuchs was born in Rüsselsheim , Grand Duchy of Hesse , on 29 December 1911 , the third of four children of a Lutheran pastor , Emil Fuchs , and his wife Else Wagner . Fuchs was always known by his last given name , Klaus . He had an older brother Gerhard , an older sister Elisabeth , and a younger sister , Kristel . The family moved to Eisenach , where he attended the gymnasium , and took his " abitur " . At school , Fuchs and his siblings were taunted over his father ' s unpopular political views , which they came to share . They became known as the " red foxes " , Fuchs being the German word for fox . Fuchs entered the University of Leipzig in 1930 , where his father was a professor of theology . He became involved in student politics , joining the student branch of the Social Democratic Party of Germany ( SPD ) , a party that his father had joined in 1912 , and the " Reichsbanner Schwarz - Rot - Gold " , the party ' s paramilitary organisation . His father took up a new position as professor of religion at the Pedagogical Academy in Kiel , and in the autumn Fuchs transferred to the University of Kiel , which his brother Gerhard and sister Elisabeth also attended , and continued his studies in mathematics and physics . In October 1931 , his mother committed suicide by drinking hydrochloric acid . The family later discovered that her mother had also taken her own life . In the March 1932 German presidential election , the SPD supported Paul von Hindenburg for president , fearing that a split vote would hand the job to the National Socialist German Workers ' Party ( NSDAP ) candidate , Adolf Hitler . However , when the Communist Party of Germany ( KPD ) ran its own candidate , Ernst Thälmann , Fuchs offered to speak for him , and was expelled from the SPD . That year Fuchs and all three of his siblings joined the KPD . Fuchs and his brother Gerhard were active speakers at public meetings , and occasionally attempted to disrupt NSDAP gatherings . At one such gathering , Fuchs was beaten up and thrown into the river . When Hitler became Chancellor of Germany in January 1933 , Fuchs decided to leave Kiel , where the NSDAP was particularly strong , and he was a well - known KPD member , and he enrolled at the Kaiser Wilhelm Institute for Physics in Berlin . On 28 February , he took an early train to Berlin for a KPD meeting there . On the train , he read about the Reichstag fire in a newspaper . Fuchs correctly assumed that opposition parties would be blamed for the fire , and quietly removed his hammer and sickle lapel pin . The KPD meeting in Berlin was held in secret . Fellow party members urged him to continue his studies in another country . He went into hiding for five months in the apartment of a fellow party member . In August 1933 , he attended an anti - fascist conference in Paris chaired by Henri Barbusse , where he met an English couple , Ronald and Jessie Gunn , who invited Fuchs to stay with them in Clapton , Somerset . He was eventually expelled from the Kaiser Wilhelm Institute in October 1933 . Fuchs arrived in England on 24 September 1933 . Jessie Gunn was a member of the Wills family , the heirs to Imperial Tobacco and benefactors of the University of Bristol . She arranged for Fuchs to meet Nevill Mott , Bristol ' s professor of physics , and he agreed to take Fuchs on as a research assistant . Fuchs earned his Ph . D . in physics there in 1937 . A paper on " A Quantum Mechanical Calculation for the Elastic Constance of Monovalent Metals " was published in the " Proceedings of the Royal Society " in 1936 . By this time Mott had a number of German refugees working for him , and lacked positions for them all . He did not think that Fuchs would make much of a teacher , so he arranged a research post for Fuchs , at the University of Edinburgh working under Max Born , who was himself a German refugee . Fuchs published papers with Born on " The Statistical Mechanics of Condensing Systems " and " On Fluctuations in Electromagnetic radiation " in the " Proceedings of the Royal Society " . He also received a Doctorate in Science degree from Edinburgh . Fuchs proudly mailed copies back to his father in Germany . In Germany , Emil had been dismissed from his academic post , and , disillusioned with the Lutheran Church ' s support of the NSDAP , had become a Quaker in 1933 . He was arrested for speaking out against the government , but was only held for one month . Elisabeth married a fellow communist , Gustav Kittowski , with whom she had a child they named Klaus . Elisabeth and Kittowski were arrested in 1933 , and sentenced to 18 months imprisonment , but were freed at Christmas . Gerhard and his wife Karin were arrested in 1934 , and spent the next two years in prison . Gerhard , Karin , Elisabeth and Kittowski established a car rental agency in Berlin , which they used to smuggle Jews and opponents of the government out of Germany . After Emil was arrested in 1933 , Kristel fled to Zurich , where she studied education and psychology at the University of Zurich . She returned to Berlin in 1934 , where she too worked at the car rental agency . In 1936 , Emil arranged with Quaker friends in the United States for Kristel to attend Swarthmore College there . She visited Fuchs in England " en route " to America , where she eventually married an American communist , Robert Heineman , and settled in Cambridge , Massachusetts . She became a permanent resident in the United States in May 1938 . In 1936 , Kittowski and Elisabeth was arrested again , and the rental cars were impounded . Gerhard and Karin fled to Czechoslovakia . Elisabeth was released and went to live with Emil , while Kittowski , sentenced to six years , later escaped from prison and also made his way to Czechoslovakia . In March 1939 , Elisabeth committed suicide by throwing herself from a train , leaving Emil to raise young Klaus . Second World War . Fuchs applied to become a British citizen 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 internment on the Isle of Man . In July , he was sent to an internment camp in Sherbrooke , Quebec , Canada , where he joined a communist discussion group led by Hans Kahle . Kahle was a KPD member who had fought in the Spanish Civil War . After fleeing to Britain with his family , Kahle had helped Jurgen Kuczynski organise the KPD in Britain . Kristel arranged for Israel Halperin , the brother - in - law of a friend of hers , Wendell Furry , to bring Fuchs some magazines . 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 . Fuchs returned to Edinburgh in January , and resumed working for Born . During 1940 , he published four more papers with Born on " 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 " . On May 1941 , he was approached by Rudolf Peierls of the University of Birmingham to work on the " Tube Alloys " program – the British atomic bomb research project . Despite wartime restrictions , he was granted British citizenship on 7 August 1942 and signed an Official Secrets Act declaration form . As accommodation was scarce in wartime Birmingham , he stayed with Rudolf and Genia Peierls . Soon after , Fuchs contacted Jurgen Kuczynski , who was now teaching at the London School of Economics . Kuczynski put him in contact with Simon Davidovitch Kremer ( codename : " Alexander " ) the secretary to the military attaché at the Soviet Union ' s embassy , who worked for the 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 Ruth Kuczynski ( codename : " Sonia " ) the sister of Jurgen Kuczynski – a German communist and a major in Soviet Military Intelligence . She was an experienced agent who had worked with Richard Sorge ' s spy ring in the Far East . In late 1943 , Fuchs ( codename : " Rest " ; he became " Charles " in May 1944 ) 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 . 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 . He was contacted by Harry Gold ( codename : " Raymond " ) , an NKGB agent in early 1944 . 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 . He was the author of techniques ( such as the still - used Fuchs - Nordheim method ) for calculating the energy of a fissile assembly which goes highly prompt critical . Later , he also filed a patent with John von Neumann , describing a method to initiate fusion in a thermonuclear weapon with an implosion trigger . Fuchs was one of the many Los Alamos scientists present at the Trinity test . Fuchs , who was known as " Karl " rather than " Klaus " at Los Alamos , dated grade school teachers Evelyn Kline and Jean Parker . He befriended Richard Feynman . Fuchs and Peierls were the only members of the British Mission to Los Alamos who owned cars , and Fuchs loaned his Buick to Feynman so Feynman could visit his dying wife in hospital in Albuquerque . At the request of Norris Bradbury , who had replaced Robert Oppenheimer as director of the Los Alamos Laboratory in October 1945 , Fuchs stayed on at the laboratory into 1946 to help with preparations for Operation Crossroads . He was no less highly regarded by the British , who wanted him to return to the United Kingdom to work on Britain ' s nuclear weapons program . As Anglo - American cooperation broke down , Fuchs spied on the Americans for Britain . Fuchs began working at the Atomic Energy Research Establishment at Harwell , in August 1946 , where he became the head of the Theoretical Physics Division . From late 1947 to May 1949 , he gave Alexander Feklisov , his case officer , the principal theoretical outline for creating a hydrogen bomb and the initial drafts for its development as the work progressed in England and America . Meeting with Feklisov six times , he provided the results of the test at Eniwetok atoll of uranium and plutonium bombs and the key data on production of uranium - 235 . Fuchs later testified that he passed detailed information on the project to the Soviet Union through courier Harry Gold in 1945 , and further information about Edward Teller ' s unworkable " Super " design for a hydrogen bomb in 1946 and 1947 . Fuchs attended a conference of the Combined Policy Committee ( CPC ) in 1947 , a committee created to facilitate exchange of atomic secrets at the highest levels of governments of the United States , Great Britain and Canada ; Donald Maclean , as British co - secretary of CPC , was also in attendance . Under interrogation by MI5 officer William Skardon at an informal meeting in December 1949 , Fuchs initially denied being a spy and was not detained . In January 1950 , Fuchs arranged another interview with Skardon and voluntarily confessed that he was a spy . Fuchs told interrogators the NKGB acquired an agent in Berkeley , California , who informed the Soviet Union about electromagnetic separation research of uranium - 235 in 1942 or earlier . Fuchs ' statements to British and American intelligence agencies were used to implicate Harry Gold , a key witness in the trials of David Greenglass and Julius and Ethel Rosenberg in the United States . Value of Fuchs ' data to the Soviet project . Hans Bethe once said that Klaus Fuchs was the only physicist he knew who truly changed history . Because the head of the Soviet project , Lavrenti Beria , used foreign intelligence as a third - party check , rather than giving it directly to the scientists , as he did not trust the information by default , it is unknown whether Fuchs ' s fission information had a substantial effect . Considering that the pace of the Soviet program was set primarily by the amount of uranium they could procure , it is hard for scholars to accurately judge how much time this saved . Whether the information Fuchs passed relating to the hydrogen bomb would have been useful is still somewhat in debate . Most scholars have agreed with the assessment made by Hans Bethe in 1952 , which concluded that by the time Fuchs left the thermonuclear program — the summer of 1946 — there was too little known about the mechanism of the hydrogen bomb for his information to be of any necessary use to the Soviet Union ( the successful Teller - Ulam design was not devised until 1951 ) . Soviet physicists later noted that they could see as well as the Americans eventually did that the early designs by Fuchs and Edward Teller were useless . However , later archival work by the Soviet physicist German Goncharov has suggested that while Fuchs ' early work ( most of which is still classified in the United States , but copies of which were available to the Soviets ) did not aid the Soviets in their effort towards the hydrogen bomb , it was actually far closer to the final correct solution than was recognized at the time , and indeed spurred Soviet research into useful problems which eventually resulted in the correct answer . Since most of Fuchs ' work on the bomb , including a 1946 patent on a particular model for the weapon , are still classified in the United States , it has been difficult for scholars to fully assess these conclusions . In any case , it seems clear that Fuchs could not have just given the Soviets the " secret " to the hydrogen bomb , since he did not himself actually know it . Later life . Fuchs ' espionage likely cancelled an Anglo - American plan in 1950 for Britain to receive American - made atomic bombs . He was prosecuted by Sir Hartley Shawcross and was convicted on 1 March 1950 . After a trial lasting less than 90 minutes , Lord Goddard sentenced him to fourteen years ' imprisonment , the maximum for espionage , because the Soviet Union was classed as an ally at the time . In December 1950 he was stripped of his British citizenship . The head of the British H - bomb project , Sir William Penney , visited Fuchs in prison in 1952 . Fuchs was released on 23 June 1959 , after serving nine years and four months of his sentence at Wakefield Prison and promptly emigrated to the German Democratic Republic ( East Germany ) . The tutorial he gave to Qian Sanqiang and other Chinese physicists helped them to develop the first Chinese atomic bomb the " 596 " which was tested five years later . In 1959 , he married a friend from his years as a student communist , Margarete Keilson . He continued his scientific career and achieved considerable prominence . He was elected to the Academy of Sciences and the SED central committee and was later appointed deputy director of the Institute for Nuclear Research in Rossendorf , where he served until he retired in 1979 . He received the Patriotic Order of Merit , the Order of Karl Marx and the National Prize of East Germany . He died in Berlin on 28 January 1988 and was buried in its Friedrichsfelde Cemetery .