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Klaus Emil Julius Fuchs (29 December 1911 – 28 January 1988) was a German theoretical physicist and
atomic spy Atomic spies or atom spies were people in the United States, the United Kingdom, and Canada who are known to have illicitly given information about nuclear weapons production or design to the Soviet Union during World War II and the early Col ...
who supplied information from the American, British and Canadian
Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
to the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
during and shortly after
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
. While at the
Los Alamos National Laboratory Los Alamos National Laboratory (often shortened as Los Alamos and LANL) is one of the sixteen research and development laboratories of the United States Department of Energy (DOE), located a short distance northwest of Santa Fe, New Mexico, ...
, Fuchs was responsible for many significant theoretical calculations relating to the first
nuclear weapons A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...
and, later, early models of the hydrogen bomb. After his conviction in 1950, he served nine years in prison in the United Kingdom, then migrated to
East Germany East Germany, officially the German Democratic Republic (GDR; german: Deutsche Demokratische Republik, , DDR, ), was a country that existed from its creation on 7 October 1949 until German reunification, its dissolution on 3 October 1990. In t ...
where he resumed his career as a physicist and scientific leader. The son of a
Lutheran Lutheranism is one of the largest branches of Protestantism, identifying primarily with the theology of Martin Luther, the 16th-century German monk and reformer whose efforts to reform the theology and practice of the Catholic Church launched ...
pastor, Fuchs attended the
University of Leipzig Leipzig University (german: Universität Leipzig), in Leipzig in Saxony, Germany, is one of the world's oldest universities and the second-oldest university (by consecutive years of existence) in Germany. The university was founded on 2 December ...
, where his father was a professor of
theology Theology is the systematic study of the nature of the divine and, more broadly, of religious belief. It is taught as an academic discipline, typically in universities and seminaries. It occupies itself with the unique content of analyzing th ...
, and became involved in student politics, joining the student branch of the
Social Democratic Party of Germany The Social Democratic Party of Germany (german: Sozialdemokratische Partei Deutschlands, ; SPD, ) is a centre-left social democratic political party in Germany. It is one of the major parties of contemporary Germany. Saskia Esken has been ...
(SPD), and the '' Reichsbanner Schwarz-Rot-Gold'', the SPD's
paramilitary A paramilitary is an organization whose structure, tactics, training, subculture, and (often) function are similar to those of a professional military, but is not part of a country's official or legitimate armed forces. Paramilitary units carr ...
organisation. He was expelled from the SPD in 1932, and joined the
Communist Party of Germany The Communist Party of Germany (german: Kommunistische Partei Deutschlands, , KPD ) was a major political party in the Weimar Republic between 1918 and 1933, an underground resistance movement in Nazi Germany, and a minor party in West German ...
(KPD). He went into hiding after the 1933 Reichstag fire, and fled to the United Kingdom, where he received his
PhD PHD or PhD may refer to: * Doctor of Philosophy (PhD), an academic qualification Entertainment * '' PhD: Phantasy Degree'', a Korean comic series * '' Piled Higher and Deeper'', a web comic * Ph.D. (band), a 1980s British group ** Ph.D. (Ph.D. al ...
from the
University of Bristol , mottoeng = earningpromotes one's innate power (from Horace, ''Ode 4.4'') , established = 1595 – Merchant Venturers School1876 – University College, Bristol1909 – received royal charter , type ...
under the supervision of Nevill Mott, and his DSc from the
University of Edinburgh The University of Edinburgh ( sco, University o Edinburgh, gd, Oilthigh Dhùn Èideann; abbreviated as ''Edin.'' in post-nominals) is a public research university based in Edinburgh, Scotland. Granted a royal charter by King James VI in 1 ...
, where he worked as an assistant to
Max Born Max Born (; 11 December 1882 – 5 January 1970) was a German physicist and mathematician who was instrumental in the development of quantum mechanics. He also made contributions to solid-state physics and optics and supervised the work of a ...
. After the Second World War broke out in Europe, he was interned in the
Isle of Man ) , anthem = " O Land of Our Birth" , image = Isle of Man by Sentinel-2.jpg , image_map = Europe-Isle_of_Man.svg , mapsize = , map_alt = Location of the Isle of Man in Europe , map_caption = Location of the Isle of Man (green) in Europ ...
, 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 Ursula Kuczynski, codenamed "Sonya", 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 Columbia University (also known as Columbia, and officially as Columbia University in the City of New York) is a private research university in New York City. Established in 1754 as King's College on the grounds of Trinity Church in Manhatt ...
, 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 implosion, necessary for the development of the
plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exh ...
bomb. After the war, he returned to the UK and worked at the
Atomic Energy Research Establishment The Atomic Energy Research Establishment (AERE) was the main centre for atomic energy research and development in the United Kingdom from 1946 to the 1990s. It was created, owned and funded by the British Government. A number of early res ...
at Harwell as head of the Theoretical Physics Division. In January 1950, Fuchs confessed that he had passed information to the Soviets over a seven-year period beginning in 1942. A British court
sentenced Sentenced was a Finnish gothic metal band that played melodic death metal in their early years. The band formed in 1989 in the town of Muhos and broke up in 2005. History Early years (1988–1991) Sentenced started in 1988 as Deformity and ...
him to fourteen years'
imprisonment Imprisonment is the restraint of a person's liberty, for any cause whatsoever, whether by authority of the government, or by a person acting without such authority. In the latter case it is " false imprisonment". Imprisonment does not necessar ...
and he was subsequently stripped of his British citizenship. He was released in 1959, after serving nine years, and migrated to the German Democratic Republic (East Germany), where he was elected to the Academy of Sciences and became a member of the Socialist Unity Party of Germany (SED)
central committee Central committee is the common designation of a standing administrative body of communist parties, analogous to a board of directors, of both ruling and nonruling parties of former and existing socialist states. In such party organizations, the ...
. He was later appointed deputy director of the Institute for Nuclear Research in Rossendorf, where he served until he retired in 1979.


Early life

Klaus Emil Julius Fuchs was born in Rüsselsheim,
Grand Duchy of Hesse The Grand Duchy of Hesse and by Rhine (german: link=no, Großherzogtum Hessen und bei Rhein) was a grand duchy in western Germany that existed from 1806 to 1918. The Grand Duchy originally formed from the Landgraviate of Hesse-Darmstadt in 18 ...
, on 29 December 1911, the third of four children of a
Lutheran Lutheranism is one of the largest branches of Protestantism, identifying primarily with the theology of Martin Luther, the 16th-century German monk and reformer whose efforts to reform the theology and practice of the Catholic Church launched ...
pastor, Emil Fuchs, and his wife Else Wagner. His father served in the army during
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
but later became a
pacifist Pacifism is the opposition or resistance to war, militarism (including conscription and mandatory military service) or violence. Pacifists generally reject theories of Just War. The word ''pacifism'' was coined by the French peace campai ...
and a
socialist Socialism is a left-wing economic philosophy and movement encompassing a range of economic systems characterized by the dominance of social ownership of the means of production as opposed to private ownership. As a term, it describes the ...
, joining the
Social Democratic Party of Germany The Social Democratic Party of Germany (german: Sozialdemokratische Partei Deutschlands, ; SPD, ) is a centre-left social democratic political party in Germany. It is one of the major parties of contemporary Germany. Saskia Esken has been ...
(SPD) in 1921. He eventually became a
Quaker Quakers are people who belong to a historically Protestant Christian set of denominations known formally as the Religious Society of Friends. Members of these movements ("theFriends") are generally united by a belief in each human's abili ...
. Fuchs had an older brother Gerhard, an older sister Elisabeth, and a younger sister, Kristel. The family moved to Eisenach, where Fuchs attended the '' Gymnasium'', and took his ''
Abitur ''Abitur'' (), often shortened colloquially to ''Abi'', is a qualification granted at the end of secondary education in Germany. It is conferred on students who pass their final exams at the end of ISCED 3, usually after twelve or thirteen ye ...
''. At school, Fuchs and his siblings were taunted over his father's unpopular socialist political views, which they came to share. They became known as the "red foxes", Fuchs being the German word for fox. Fuchs was left-handed, but was forced to write with his right hand. Fuchs entered the
University of Leipzig Leipzig University (german: Universität Leipzig), in Leipzig in Saxony, Germany, is one of the world's oldest universities and the second-oldest university (by consecutive years of existence) in Germany. The university was founded on 2 December ...
in 1930, where his father was a professor of
theology Theology is the systematic study of the nature of the divine and, more broadly, of religious belief. It is taught as an academic discipline, typically in universities and seminaries. It occupies itself with the unique content of analyzing th ...
. He became involved in student politics, joining the student branch of the 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 Kiel () is the capital and most populous city in the northern German state of Schleswig-Holstein, with a population of 246,243 (2021). Kiel lies approximately north of Hamburg. Due to its geographic location in the southeast of the Jutland ...
, and in the autumn Fuchs transferred to the University of Kiel, which his brother Gerhard and sister Elisabeth also attended. Fuchs continued his studies in mathematics and physics at the university. In October 1931, his mother committed suicide by drinking
hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...
. The family later discovered that his maternal grandmother had also taken her own life. In the March 1932 German presidential election, the SPD supported
Paul von Hindenburg Paul Ludwig Hans Anton von Beneckendorff und von Hindenburg (; abbreviated ; 2 October 1847 – 2 August 1934) was a German field marshal and statesman who led the Imperial German Army during World War I and later became President of Germany fr ...
for
President President most commonly refers to: *President (corporate title) * President (education), a leader of a college or university * President (government title) President may also refer to: Automobiles * Nissan President, a 1966–2010 Japanese ...
, fearing that a split vote would hand the job to the
Nazi Party The Nazi Party, officially the National Socialist German Workers' Party (german: Nationalsozialistische Deutsche Arbeiterpartei or NSDAP), was a far-right political party in Germany active between 1920 and 1945 that created and supported t ...
(NSDAP) candidate,
Adolf Hitler Adolf Hitler (; 20 April 188930 April 1945) was an Austrian-born German politician who was dictator of Germany from 1933 until his death in 1945. He rose to power as the leader of the Nazi Party, becoming the chancellor in 1933 and the ...
. However, when the
Communist Party of Germany The Communist Party of Germany (german: Kommunistische Partei Deutschlands, , KPD ) was a major political party in the Weimar Republic between 1918 and 1933, an underground resistance movement in Nazi Germany, and a minor party in West German ...
(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 The chancellor of Germany, officially the federal chancellor of the Federal Republic of Germany,; often shortened to ''Bundeskanzler''/''Bundeskanzlerin'', / is the head of the federal government of Germany and the commander in chief of the Ge ...
in January 1933, Fuchs decided to leave Kiel, where the NSDAP was particularly strong and he was a well-known KPD member. He enrolled at the
Kaiser Wilhelm Institute for Physics The Kaiser Wilhelm Society for the Advancement of Science (German: ''Kaiser-Wilhelm-Gesellschaft zur Förderung der Wissenschaften'') was a German scientific institution established in the German Empire in 1911. Its functions were taken over by ...
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 The hammer and sickle (Unicode: "☭") zh, s=锤子和镰刀, p=Chuízi hé liándāo or zh, s=镰刀锤子, p=Liándāo chuízi, labels=no is a symbol meant to represent proletarian solidarity, a union between agricultural and industr ...
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. 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 Henri Barbusse (; 17 May 1873 – 30 August 1935) was a French novelist and a member of the French Communist Party. He was a lifelong friend of Albert Einstein. Life The son of a French father and an English mother, Barbusse was born in Asnièr ...
, where he met an English couple, Ronald and Jessie Gunn, who invited Fuchs to stay with them in Clapton, Somerset. He was expelled from the Kaiser Wilhelm Institute in October 1933.


Refugee in Britain

Fuchs arrived in England on 24 September 1933. Jessie Gunn was a member of the Wills family, the heirs to
Imperial Tobacco Imperial Brands plc (formerly Imperial Tobacco Group plc), is a British multinational tobacco company headquartered in Bristol, England. It is the world's fourth-largest international cigarette company measured by market share after Philip Mo ...
and benefactors of the
University of Bristol , mottoeng = earningpromotes one's innate power (from Horace, ''Ode 4.4'') , established = 1595 – Merchant Venturers School1876 – University College, Bristol1909 – received royal charter , type ...
. 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
PhD PHD or PhD may refer to: * Doctor of Philosophy (PhD), an academic qualification Entertainment * '' PhD: Phantasy Degree'', a Korean comic series * '' Piled Higher and Deeper'', a web comic * Ph.D. (band), a 1980s British group ** Ph.D. (Ph.D. al ...
in physics there in 1937. A paper on "A Quantum Mechanical Calculation of the Elastic Constants of Monovalent Metals" was published in the ''
Proceedings of the Royal Society ''Proceedings of the Royal Society'' is the main research journal of the Royal Society. The journal began in 1831 and was split into two series in 1905: * Series A: for papers in physical sciences and mathematics. * Series B: for papers in life s ...
'' 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 The University of Edinburgh ( sco, University o Edinburgh, gd, Oilthigh Dhùn Èideann; abbreviated as ''Edin.'' in post-nominals) is a public research university based in Edinburgh, Scotland. Granted a royal charter by King James VI in 1 ...
working under
Max Born Max Born (; 11 December 1882 – 5 January 1970) was a German physicist and mathematician who was instrumental in the development of quantum mechanics. He also made contributions to solid-state physics and optics and supervised the work of a ...
, 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 Doctor of Science ( la, links=no, Scientiae Doctor), usually abbreviated Sc.D., D.Sc., S.D., or D.S., is an academic research degree awarded in a number of countries throughout the world. In some countries, "Doctor of Science" is the degree used f ...
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 Quakers are people who belong to a historically Protestant Christian set of denominations known formally as the Religious Society of Friends. Members of these movements ("theFriends") are generally united by a belief in each human's abili ...
in 1933. He was arrested for speaking out against the government and was held for a 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 Swarthmore College ( , ) is a private liberal arts college in Swarthmore, Pennsylvania. Founded in 1864, with its first classes held in 1869, Swarthmore is one of the earliest coeducational colleges in the United States. It was established as ...
there. She visited Fuchs in England ''en route'' to America, where she eventually married an American communist, Robert Heineman, and settled in
Cambridge, Massachusetts Cambridge ( ) is a city in Middlesex County, Massachusetts, United States. As part of the Boston metropolitan area, the cities population of the 2020 U.S. census was 118,403, making it the fourth most populous city in the state, behind Boston, ...
. She became a permanent resident in the United States in May 1938. In 1936, Kittowski and Elisabeth were arrested again, and the rental cars were impounded. Gerhard and Karin fled to
Czechoslovakia , rue, Чеськословеньско, , yi, טשעכאסלאוואקיי, , common_name = Czechoslovakia , life_span = 1918–19391945–1992 , p1 = Austria-Hungary , image_p1 ...
. 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 August 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 subject The term "British subject" has several different meanings depending on the time period. Before 1949, it referred to almost all subjects of the British Empire (including the United Kingdom, Dominions, and colonies, but excluding protectorates ...
in August 1939, but his application had not been processed before the
Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposi ...
broke out in Europe in September 1939. There was a classification system for enemy aliens, 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 ) , anthem = " O Land of Our Birth" , image = Isle of Man by Sentinel-2.jpg , image_map = Europe-Isle_of_Man.svg , mapsize = , map_alt = Location of the Isle of Man in Europe , map_caption = Location of the Isle of Man (green) in Europ ...
and then, in July, he was sent to an internment camps in Canada, first on the Plains of Abraham in Quebec City and later at a site near
Sherbrooke, Quebec Sherbrooke ( ; ) is a city in southern Quebec, Canada. It is at the confluence of the Saint-François and Magog rivers in the heart of the Estrie administrative region. Sherbrooke is also the name of a territory equivalent to a regional cou ...
. 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''. While interned in Quebec, he joined a communist discussion group led by Hans Kahle. Kahle was a KPD member who had fought in the
Spanish Civil War The Spanish Civil War ( es, Guerra Civil Española)) or The Revolution ( es, La Revolución, link=no) among Nationalists, the Fourth Carlist War ( es, Cuarta Guerra Carlista, link=no) among Carlism, Carlists, and The Rebellion ( es, La Rebeli ...
. After fleeing to Britain with his family, Kahle had helped
Jürgen Kuczynski Jürgen Kuczynski (; 17 September 1904, Elberfeld – 6 August 1997, Berlin) was a German economist, journalist, and communist. He also provided intelligence to the Soviet Union during World War II. By 1936, Kuczynski had followed his father ...
organise the KPD in Britain. Kristel arranged for mathematics professor Israel Halperin, the brother-in-law of a friend of hers,
Wendell H. Furry Wendell Hinkle Furry (February 18, 1907 – December 17, 1984) was a professor of physics at Harvard University who made contributions to theoretical and particle physics. The Furry theorem is named after him. Early life Furry was born in Pra ...
, 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. Fuchs returned to Edinburgh in January, and resumed working for Born. In May 1941, he was approached by Rudolf Peierls of the
University of Birmingham , mottoeng = Through efforts to heights , established = 1825 – Birmingham School of Medicine and Surgery1836 – Birmingham Royal School of Medicine and Surgery1843 – Queen's College1875 – Mason Science College1898 – Mason Univers ...
to work on the " Tube Alloys" programme – the British atomic bomb research project. Despite wartime restrictions, he became a British subject on 7 August 1942 and signed an
Official Secrets Act An Official Secrets Act (OSA) is legislation that provides for the protection of state secrets and official information, mainly related to national security but in unrevised form (based on the UK Official Secrets Act 1911) can include all infor ...
declaration form. As accommodation was scarce in wartime Birmingham, he stayed with Rudolf and Genia Peierls. Fuchs and Peierls did some important work together, which included a fundamental paper about isotope separation. Soon after, Fuchs contacted Jürgen Kuczynski, who was now teaching at the
London School of Economics , mottoeng = To understand the causes of things , established = , type = Public research university , endowment = £240.8 million (2021) , budget = £391.1 milli ...
. Kuczynski put him in contact with Simon Davidovitch Kremer (codename: "Alexander"; 1900-1991), the secretary to the military attaché at the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
's embassy, who worked for the GRU (Russian: ''Главное Разведывательное Управление''), the
Red Army The Workers' and Peasants' Red Army (Russian language, Russian: Рабо́че-крестья́нская Кра́сная армия),) often shortened to the Red Army, was the army and air force of the Russian Soviet Federative Socialist R ...
'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. In late 1943, Fuchs (codename: "Rest"; he became "Charles" in May 1944) transferred along with Peierls to
Columbia University Columbia University (also known as Columbia, and officially as Columbia University in the City of New York) is a private research university in New York City. Established in 1754 as King's College on the grounds of Trinity Church in Manhatt ...
, in New York City, to work on gaseous diffusion as a means of uranium enrichment for the
Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
. 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 Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exh ...
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 that goes highly prompt critical, and his report on blast waves is still considered a classic. Fuchs was one of the many Los Alamos scientists present at the Trinity test in July 1945. In April 1946 he attended a conference at Los Alamos that discussed the possibility of a
thermonuclear weapon A thermonuclear weapon, fusion weapon or hydrogen bomb (H bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lo ...
; one month later, he filed a patent with
John von Neumann John von Neumann (; hu, Neumann János Lajos, ; December 28, 1903 – February 8, 1957) was a Hungarian-American mathematician, physicist, computer scientist, engineer and polymath. He was regarded as having perhaps the widest c ...
, describing a method to initiate fusion in a thermonuclear weapon with an implosion trigger. Bethe considered Fuchs "one of the most valuable men in my division" and "one of the best theoretical physicists we had." 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 lent his
Buick Buick () is a division of the American automobile manufacturer General Motors (GM). Started by automotive pioneer David Dunbar Buick in 1899, it was among the first American marques of automobiles, and was the company that established General ...
to Feynman so Feynman could visit his dying wife in hospital in
Albuquerque Albuquerque ( ; ), ; kee, Arawageeki; tow, Vakêêke; zun, Alo:ke:k'ya; apj, Gołgéeki'yé. abbreviated ABQ, is the most populous city in the U.S. state of New Mexico. Its nicknames, The Duke City and Burque, both reference its founding i ...
. Klaus Fuchs's main courier was Harry Gold. 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' 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." Gold reported after his first meeting with Klaus Fuchs:


Post-war activities

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 the Operation Crossroads weapons tests. The US
Atomic Energy Act of 1946 The Atomic Energy Act of 1946 (McMahon Act) determined how the United States would control and manage the nuclear technology it had jointly developed with its World War II allies, the United Kingdom and Canada. Most significantly, the Act ru ...
(McMahon Act) prohibited the transfer of information on nuclear research to any foreign country, including Britain, without explicit official authority, and Fuchs supplied highly classified U.S. information to nuclear scientists in Britain and to his Soviet contacts. , British official files on Fuchs were still being withheld. As of 2020, the National Archives listed one dossier on Fuchs, KV 2/1263, including the "Prosecution file. With summary of early interrogations ... and details of the scientifical/technical information passed to the Russians". The date of release of this material was not stated. According to an October 2020 book review, author Nancy Thorndike Greenspan "appears to have had access to some of the Fuchs files that have been withheld at Kew, such as the AB/1 series, which has been closed for access for most human beings". Fuchs was highly regarded as a scientist by the British, who wanted him to return to the United Kingdom to work on Britain's postwar nuclear weapons programme. He returned in August 1946 and became the head of the Theoretical Physics Division at the
Atomic Energy Research Establishment The Atomic Energy Research Establishment (AERE) was the main centre for atomic energy research and development in the United Kingdom from 1946 to the 1990s. It was created, owned and funded by the British Government. A number of early res ...
at Harwell. From late 1947 to May 1949 he gave
Alexander Feklisov Aleksandr Semyonovich Feklisov (Russian: Александр Семёнович Феклисов; 9 March 1914 – 26 October 2007) was a Soviet spy, the NKVD Case Officer who handled Julius Rosenberg and Klaus Fuchs, among others. Life and work ...
, his Soviet 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 Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exi ...
. Also in 1947, Fuchs attended a conference of the
Combined Policy Committee The Quebec Agreement was a secret agreement between the United Kingdom and the United States outlining the terms for the coordinated development of the science and engineering related to nuclear energy and specifically nuclear weapons. It was ...
(CPC), which was created to facilitate exchange of atomic secrets at the highest levels of governments of the United States, United Kingdom and Canada. Donald Maclean, another Soviet spy, was also in attendance as British co-secretary of CPC.


Detection and confession

By September 1949, information from the
Venona project The Venona project was a United States counterintelligence program initiated during World War II by the United States Army's Signal Intelligence Service (later absorbed by the National Security Agency), which ran from February 1, 1943, until Oc ...
indicated to GCHQ that Fuchs was a spy, but the British intelligence services were wary of indicating the source of their information. The Soviets had broken off contact with him in February. Fuchs may have been subsequently tipped off by
Kim Philby Harold Adrian Russell "Kim" Philby (1 January 191211 May 1988) was a British intelligence officer and a double agent for the Soviet Union. In 1963 he was revealed to be a member of the Cambridge Five, a spy ring which had divulged British s ...
. After a great deal of research for his 2019 biography, ''Trinity'', Frank Close confirmed that while MI5 suspected Fuchs for over two years, "it was decrypters at GCHQ who supplied clear proof of his guilt ... not the crack American team that is normally given all the credit", according to a review of the book. Under interrogation by MI5 officer
William Skardon William James Skardon (1904–1987) was a Special Branch officer who joined MI5 in 1940 and became an interrogator and head of "The Watchers" (physical surveillance teams). He was intimately involved with the investigation of the Cambridge Five a ...
at an informal meeting in December 1949, Fuchs initially denied being a spy and was not detained. According to Nancy Thorndike Greenspan, author of a 2020 book, ''Atomic Spy: The Dark Lives of Klaus Fuchs'', Skardon told Fuchs that if he admitted his earlier espionage activity, he could be permitted to continue to work at Harwell. In October 1949, Fuchs had approached Henry Arnold, the head of security at Harwell, with the news that his father had been given a chair at the
University of Leipzig Leipzig University (german: Universität Leipzig), in Leipzig in Saxony, Germany, is one of the world's oldest universities and the second-oldest university (by consecutive years of existence) in Germany. The university was founded on 2 December ...
in
East Germany East Germany, officially the German Democratic Republic (GDR; german: Deutsche Demokratische Republik, , DDR, ), was a country that existed from its creation on 7 October 1949 until German reunification, its dissolution on 3 October 1990. In t ...
, and this information became a factor as well. In early January Fuchs was informed that he must resign his position at Harwell because of his father’s appointment in East Germany. He was offered help in finding a university post. Meeting with Skardon for a fourth time on 24 January 1950, Fuchs voluntarily confessed that he had shared information with the Soviets. According to Nancy Thorndike Greenspan, Skardon’s report on their meeting “made no mention of his promise to Fuchs to stay on at Harwell if he confessed,” but at the subsequent debfriefing it was agreed “to maintain FUCHS in his present state of mind, and for this state of mind to be in no way disturbed”. To make it possible to prosecute Fuchs, Skardon proposed that Fuchs be asked to prepare a signed statement, which he then did at the War Office in London. The document included the statement “I was given the chance of admitting it and staying at Harwell or clearing out.” Three days later, he also directed a statement more technical in content to Michael Perrin, the deputy controller of atomic energy within the Ministry of Supply. Fuchs told interrogators that the NKGB had acquired an agent in
Berkeley, California Berkeley ( ) is a city on the eastern shore of San Francisco Bay in northern Alameda County, California, United States. It is named after the 18th-century Irish bishop and philosopher George Berkeley. It borders the cities of Oakland and E ...
, who had informed the Soviet Union about electromagnetic separation research of uranium-235 in 1942 or earlier. Fuchs's 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 Julius Rosenberg (May 12, 1918 – June 19, 1953) and Ethel Rosenberg (; September 28, 1915 – June 19, 1953) were American citizens who were convicted of spying on behalf of the Soviet Union. The couple were convicted of providing top-secret i ...
in the United States. Fuchs later stated 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 also stated that "The last time when I handed over information
o Russian authorities O, or o, is the fifteenth letter and the fourth vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''o'' (pronounced ), pl ...
was in February or March 1949". Fuchs was arrested on 2 February 1950, charged with violations of the Official Secrets Act. Nancy Thorndike Greenspan quotes from police notes on a visit between fellow scientist Peierls and Fuchs in detention shortly after the news of the arrest broke. When Peierls asked Fuchs why he had spied, Fuchs answered: "Knowledge of atomic research should not be the private property of any one country but should be shared with the rest of the world for the benefit of mankind." According to a ''
New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid ...
'' review by the conservative historian
Ronald Radosh Ronald Radosh ( ; born 1937) is an American writer, professor, historian, and former Marxist. As he described in his memoirs, Radosh was, like his parents, a member of the Communist Party of the United States of America until the Khrushchev Thaw ...
, Greenspan argues that "his goal became to balance world power and to prevent nuclear blackmail." Radosh states that "this was a post facto justification. The reason Fuchs spied was simply that he was a Communist and a true believer in Stalin and the Soviet Union".


Value of data to Soviet project

Hans Bethe once said that Klaus Fuchs was the only physicist he knew to have truly changed history. Because the head of the Soviet project,
Lavrenti Beria Lavrentiy Pavlovich Beria (; rus, Лавре́нтий Па́влович Бе́рия, Lavréntiy Pávlovich Bériya, p=ˈbʲerʲiə; ka, ლავრენტი ბერია, tr, ;  – 23 December 1953) was a Georgian Bolshevik ...
, 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 that it could procure, it is difficult for scholars to judge accurately how much time was saved. According to ''On a Field of Red'', a history of the
Comintern The Communist International (Comintern), also known as the Third International, was a Soviet-controlled international organization founded in 1919 that advocated world communism. The Comintern resolved at its Second Congress to "struggle by ...
(Communist International) by Anthony Cave Brown and
Charles B. MacDonald Charles Blair Macdonald (November 14, 1855 – April 21, 1939) was a major figure in early American golf. He built the first 18-hole course in the United States, was a driving force in the founding of the United States Golf Association, won the f ...
, Fuchs's greatest contribution to the Soviets may have been disclosing how uranium could be processed for use in a bomb. Fuchs gave Gold technical information in January 1945 that was acquired only after two years of experimentation at a cost of $400 million. Fuchs also disclosed the amount of uranium or plutonium the Americans planned to use in each atomic bomb. Whether the information Fuchs passed relating to the hydrogen bomb would have been useful is still debated. Most scholars agree with Hans Bethe's 1952 assessment, which concluded that by the time Fuchs left the thermonuclear program in mid-1946, too little was known about the mechanism of the hydrogen bomb for his information to be useful 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 would that the early designs by Fuchs and Edward Teller were useless. Later archival work by the Soviet physicist
German Goncharov German Arsenyevich Goncharov ussian: Гончаров Герман Арсеньевич(8 July 1928 – 7 September 2009) was a Soviet and Russian nuclear physicist, engineer and mathematician. He was a key member of the theoretical team which ...
suggested that Fuchs's early work did not help Soviet efforts towards the hydrogen bomb, but it was closer to the final correct solution than anyone recognised at the time. It also indeed spurred Soviet research into useful problems that eventually provided the correct answer. 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 actually know it himself. In his 2019 book, ''Trinity: The Treachery and Pursuit of the Most Dangerous Spy in History'',
Frank Close Francis Edwin Close, (born 24 July 1945) is a particle physicist who is Emeritus Professor of Physics at the University of Oxford and a Fellow of Exeter College, Oxford. Education Close was a pupil at King's School, Peterborough (then a gra ...
asserts that "it was primarily Fuchs who enabled the Soviets to catch up with Americans" in the race for the nuclear bomb. The author of the 2020 book ''Atomic Spy'' gives his efforts less value. Nancy Thorndike Greenspan suggests that the Soviets would have developed their bomb even without his help, "though probably not until 1951". On the other hand, the earlier development of the Soviet bomb may have had one significant benefit to the world, a balance of power; the author is convinced that this prevented the United States from using their bomb on
North Korea North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korean Peninsula and shares borders with China and Russia to the north, at the Yalu (Amnok) and T ...
. It is likely that Fuchs's espionage led the U.S. to cancel a 1950 Anglo-American plan to give Britain American-made atomic bombs.


Trial and imprisonment

Fuchs was prosecuted by Sir
Hartley Shawcross Hartley William Shawcross, Baron Shawcross, (4 February 1902 – 10 July 2003), known from 1945 to 1959 as Sir Hartley Shawcross, was an English barrister and Labour politician who served as the lead British prosecutor at the Nuremberg War ...
and was convicted on 1 March 1950 of four counts of breaking the
Official Secrets Act An Official Secrets Act (OSA) is legislation that provides for the protection of state secrets and official information, mainly related to national security but in unrevised form (based on the UK Official Secrets Act 1911) can include all infor ...
by "communicating information to a potential enemy." Fuchs had entered guilty pleas, and his attorney
Derek Curtis-Bennett Frederick Henry Derek Curtis-Bennett, QC (29 February 1904 – July 1956) was a British barrister who defended some of the most notorious characters in British legal history, but whose career was cut short by alcoholism. His father was Sir Henry ...
limited his case to a general plea for mitigation on the grounds of his state of mind and desire to assist the Soviets in defeating the Nazis and winning the war. Fuchs consented to the advice not to raise the question of inducement in his decision to admit guilt. After a
trial In law, a trial is a coming together of parties to a dispute, to present information (in the form of evidence) in a tribunal, a formal setting with the authority to adjudicate claims or disputes. One form of tribunal is a court. The tribun ...
lasting less than 90 minutes that was based on his confession, Lord Goddard sentenced Fuchs to 14 years'
imprisonment Imprisonment is the restraint of a person's liberty, for any cause whatsoever, whether by authority of the government, or by a person acting without such authority. In the latter case it is " false imprisonment". Imprisonment does not necessar ...
, the maximum for
espionage Espionage, spying, or intelligence gathering is the act of obtaining secret or confidential information ( intelligence) from non-disclosed sources or divulging of the same without the permission of the holder of the information for a tang ...
, because the Soviet Union was classed as an ally at the time. In February 1951, he was formally stripped of his British citizenship. The head of the British H-bomb project, Sir
William Penney William George Penney, Baron Penney, (24 June 19093 March 1991) was an English mathematician and professor of mathematical physics at the Imperial College London and later the rector of Imperial College London. He had a leading role in the ...
, visited Fuchs in prison in 1952. While imprisoned, Fuchs was friendly with the
Irish Republican Army The Irish Republican Army (IRA) is a name used by various paramilitary organisations in Ireland throughout the 20th and 21st centuries. Organisations by this name have been dedicated to irredentism through Irish republicanism, the belief th ...
prisoner Seamus Murphy with whom he played chess and helped to escape. Fuchs was released on 23 June 1959 after he had served nine years and four months of his sentence (as was then required in England where long-term prisoners were entitled by law to one third off for good behaviour in prison) at
Wakefield Prison His Majesty's Prison Wakefield is a Category A men's prison in Wakefield, West Yorkshire, England, operated by His Majesty's Prison Service. The prison has been nicknamed the "Monster Mansion" due to the large number of high-profile, high-risk ...
and promptly emigrated to the
German Democratic Republic German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **G ...
(GDR).


Career in East Germany

On arrival at
Berlin Schönefeld Airport Berlin Schönefeld Airport () (formerly ) was the secondary international airport of Berlin, the capital of Germany. It was located southeast of Berlin near the town of Schönefeld in the state of Brandenburg and bordered Berlin's southern bo ...
in the GDR, Fuchs was met by Grete (Margarete) Keilson, a friend from his years as a student communist. They were married on 9 September 1959. In the GDR, Fuchs continued his scientific career and achieved considerable prominence as a leader of research. He became a member of the SED
central committee Central committee is the common designation of a standing administrative body of communist parties, analogous to a board of directors, of both ruling and nonruling parties of former and existing socialist states. In such party organizations, the ...
in 1967, and in 1972 was elected to the Academy of Sciences where from 1974 to 1978 he was the head of the research area of physics, nuclear and materials science; he was then appointed deputy director of the Institute for Nuclear Research in Rossendorf, where he served until he retired in 1979. From 1984, Fuchs was head of the scientific councils for energetic basic research and for fundamentals of microelectronics. He received the Patriotic Order of Merit, the Order of Karl Marx and the
National Prize of East Germany The National Prize of the German Democratic Republic (East Germany) (german: Nationalpreis der Deutschen Demokratischen Republik) was an award of the German Democratic Republic (GDR) given out in three different classes for scientific, artistic, ...
. In ''The Nuclear Express: A Political History of the Bomb and Its Proliferation'' (2009) by Thomas Reed and Daniel Stillman, it is argued that a tutorial Fuchs 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. Three historians of nuclear weapons history, Robert S. Norris,
Jeremy Bernstein Jeremy Bernstein (born December 31, 1929, in Rochester, New York) is an American theoretical physicist and popular science writer. Early life Bernstein's parents, Philip S. Bernstein, a Reform rabbi, and Sophie Rubin Bernstein named him after th ...
, and
Peter D. Zimmerman Peter D. Zimmerman (June 15, 1941, Portsmouth, Virginia – August 27, 2021 Washington, D. C.) was an American nuclear physicist, arms control expert, and former Chief Scientist of the Senate Foreign Relations Committee. At his death, he was Eme ...
, challenged this particular assertion as "unsubstantiated conjecture" and asserted that ''The Nuclear Express'' is "an ambitious but deeply flawed book".


Death

Fuchs died in Berlin on 28 January 1988. He was cremated and his ashes buried in the "Pergolenweg" of the Socialists' Memorial in Berlin's Friedrichsfelde Cemetery.


In popular culture

A documentary film about Fuchs, ''Väter der tausend Sonnen'' (''Fathers of a Thousand Suns''), was released in 1990. In 2022 Fuchs was the primary focus of the second season of the
BBC World Service The BBC World Service is an international broadcaster owned and operated by the BBC, with funding from the British Government through the Foreign Secretary's office. It is the world's largest external broadcaster in terms of reception a ...
's podcast The Bomb.


Notes


References

* * * * * * * * * * * * * * * * * * *


Further reading

* (discusses the case of Fuchs, based on now available MI5 'Personal Files') * * (discusses use of Fuchs's passed on information by Soviets, based on now-declassified files)


External links


1994 Audio Interview with Robert Lamphere by Richard Rhodes on interrogating Klaus Fuchs
Voices of the Manhattan Project
Visit the Cold War International History Project (CWIHP)
for the full text of Alexander Vassiliev's Notebooks containing more information on Fuchs's involvement in espionage
FBI file on Klaus Fuchs






* ttp://nuclearweaponarchive.org/Russia/Fuchs.html Klaus Fuchsat Carey Sublette's NuclearWeaponArchive.org, which includes information about the specific information given by Fuchs to the Soviets from declassified KGB files
''Venona: Soviet Espionage and the American Response''
(
CIA The Central Intelligence Agency (CIA ), known informally as the Agency and historically as the Company, is a civilian foreign intelligence service of the federal government of the United States, officially tasked with gathering, processing, ...
publication), contains letter from agents in 1949 about Klaus Fuchs. * {{DEFAULTSORT:Fuchs, Klaus 1911 births 1950 in international relations 1988 deaths Academics of the University of Birmingham Alumni of the University of Bristol British defectors to East Germany British nuclear physicists British people convicted of spying for the Soviet Union British spies for the Soviet Union British physicists Cold War spies Communist Party of Germany politicians East German scientists 20th-century German physicists German spies for the Soviet Union Manhattan Project people Nuclear secrecy Nuclear weapons program of the Soviet Union People associated with the nuclear weapons programme of the United Kingdom People from Rüsselsheim People from the Grand Duchy of Hesse People interned in the Isle of Man during World War II Denaturalized citizens of the United Kingdom Recipients of the National Prize of East Germany Recipients of the Patriotic Order of Merit Reichsbanner Schwarz-Rot-Gold members Social Democratic Party of Germany politicians Socialist Unity Party of Germany politicians Members of the German Academy of Sciences at Berlin