Who was John Cairncross?

John Cairncross (1913–1995) was a British civil servant and literary scholar who was identified as the "fifth man" in the Cambridge spy ring, along with Kim Philby, Guy Burgess, Donald Maclean, and Anthony Blunt. Cairncross, a graduate of the University of Glasgow, entered the Foreign Office in 1936. Shortly after, he was introduced to a Soviet agent and began aiding the antifascist movement. During World War II, he smuggled decrypted German communications to the Soviets, including vital messages that helped the Red Army prepare for the Battle of Kursk. After the war, Cairncross returned to the Treasury but resigned in 1951 after being interrogated by MI5. He then pursued a career as a literary scholar, teaching in the United States and working for the United Nations Food and Agriculture Organization in Rome. In 1964, he confessed to espionage but was not prosecuted. Cairncross maintained that he never betrayed secrets that damaged Britain.

What kind of work did John Cairncross do as a civil servant?

John Cairncross, a British civil servant and spy, entered the Foreign Office in 1936 and later moved to the Treasury in 1938. In 1940, he became the private secretary to Sir Maurice Hankey in the Cabinet Office. During World War II, he was assigned to Bletchley Park as a German translator, where he smuggled decrypted German communications to the Soviets. In 1944, Cairncross transferred to MI6, Britain’s foreign intelligence agency, and in 1945, he returned to the Treasury. After the war, he may have passed NATO plans to the Soviets. He resigned from the Civil Service in 1951.

Why is John Cairncross known as a spy?

John Cairncross is known as a spy because he was identified as the "fifth man" in the Cambridge spy ring, which included Kim Philby , Guy Burgess, Donald Maclean, and Anthony Blunt. Recruited into the antifascist movement by a Soviet agent in 1936, he passed crucial information to the Soviets during World War II, including decrypted German communications that aided the Red Army in the Battle of Kursk. Although he initially denied spying when interrogated in 1951, he confessed in 1964 after Philby's defection. To avoid prosecution, he agreed to remain silent about his past.

What was the Cambridge Five spy ring, and how was John Cairncross connected to it?

The Cambridge Five was a spy ring of British men recruited in the 1930s at the University of Cambridge to become Soviet agents. The group included Kim Philby, Guy Burgess, Donald Maclean, and Anthony Blunt. John Cairncross was identified much later as the "fifth man". Cairncross, a civil servant, passed information to the Soviets, including decrypted German communications during World War II, and later, possibly NATO plans. He confessed to espionage in 1964 but was never prosecuted.

How did John Cairncross pass information to the Soviet Union?

John Cairncross, a British civil servant and member of the Cambridge spy ring, passed information to the Soviet Union by acting as a spy. After being introduced to a Soviet agent by James Klugmann, Cairncross began his espionage activities. In 1940, while working in the Cabinet Office, he may have provided the Soviets with a copy of the MAUD report, which assessed Britain's atomic bomb prospects. Later, at Bletchley Park, he smuggled decrypted German military communications to the Soviets, including vital messages that helped the Red Army prepare for the Battle of Kursk in 1943. Even after transferring to MI6 in 1944, Cairncross continued to pass information to the Soviets, and after the war, he may have given them plans for the new NATO alliance.

What impact did John Cairncross’s actions have on World War II and the postwar period?

John Cairncross, a British civil servant and member of the Cambridge spy ring, significantly aided the Soviet Union during World War II by passing along vital intelligence. As a German translator at Bletchley Park, he smuggled decrypted German communications to the Soviets, including information that helped the Red Army prepare for the Battle of Kursk in 1943. After the war, he may have passed NATO plans to the Soviets. Exposed in 1951, he resigned but later confessed to espionage in 1964. His actions provided critical support to the Soviet war effort, though he maintained he never betrayed British interests.

John Cairncross

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Germany invades Poland, September 1, 1939, using 45 German divisions and aerial attack. By September 20, only Warsaw held out, but final surrender came on September 29.

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Born:: July 25, 1913, Lesmahagow, Scotland

Died:: October 8, 1995, Herefordshire, England (aged 82)

Role In:: World War II

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John Cairncross

British civil servant and spy

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Last updated

Oct. 4, 2026 •History

Top Questions

Who was John Cairncross?
John Cairncross (1913–1995) was a British civil servant and literary scholar who was identified as the "fifth man" in the Cambridge spy ring, along with Kim Philby, Guy Burgess, Donald Maclean, and Anthony Blunt.

Cairncross, a graduate of the University of Glasgow, entered the Foreign Office in 1936. Shortly after, he was introduced to a Soviet agent and began aiding the antifascist movement. During World War II, he smuggled decrypted German communications to the Soviets, including vital messages that helped the Red Army prepare for the Battle of Kursk.

After the war, Cairncross returned to the Treasury but resigned in 1951 after being interrogated by MI5. He then pursued a career as a literary scholar, teaching in the United States and working for the United Nations Food and Agriculture Organization in Rome. In 1964, he confessed to espionage but was not prosecuted. Cairncross maintained that he never betrayed secrets that damaged Britain.
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1. John Cairncross
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What kind of work did John Cairncross do as a civil servant?
John Cairncross, a British civil servant and spy, entered the Foreign Office in 1936 and later moved to the Treasury in 1938. In 1940, he became the private secretary to Sir Maurice Hankey in the Cabinet Office. During World War II, he was assigned to Bletchley Park as a German translator, where he smuggled decrypted German communications to the Soviets. In 1944, Cairncross transferred to MI6, Britain’s foreign intelligence agency, and in 1945, he returned to the Treasury. After the war, he may have passed NATO plans to the Soviets. He resigned from the Civil Service in 1951.
1 Britannica Source
1. John Cairncross
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Why is John Cairncross known as a spy?
John Cairncross is known as a spy because he was identified as the "fifth man" in the Cambridge spy ring, which included Kim Philby, Guy Burgess, Donald Maclean, and Anthony Blunt.

Recruited into the antifascist movement by a Soviet agent in 1936, he passed crucial information to the Soviets during World War II, including decrypted German communications that aided the Red Army in the Battle of Kursk. Although he initially denied spying when interrogated in 1951, he confessed in 1964 after Philby's defection. To avoid prosecution, he agreed to remain silent about his past.
1 Britannica Source
1. John Cairncross
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What was the Cambridge Five spy ring, and how was John Cairncross connected to it?
The Cambridge Five was a spy ring of British men recruited in the 1930s at the University of Cambridge to become Soviet agents. The group included Kim Philby, Guy Burgess, Donald Maclean, and Anthony Blunt.

John Cairncross was identified much later as the "fifth man". Cairncross, a civil servant, passed information to the Soviets, including decrypted German communications during World War II, and later, possibly NATO plans. He confessed to espionage in 1964 but was never prosecuted.
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1. Spies Like Us: 10 Famous Names in the Espionage Game: The Cambridge Spy Ring
2. John Cairncross
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How did John Cairncross pass information to the Soviet Union?
John Cairncross, a British civil servant and member of the Cambridge spy ring, passed information to the Soviet Union by acting as a spy.

After being introduced to a Soviet agent by James Klugmann, Cairncross began his espionage activities. In 1940, while working in the Cabinet Office, he may have provided the Soviets with a copy of the MAUD report, which assessed Britain's atomic bomb prospects.

Later, at Bletchley Park, he smuggled decrypted German military communications to the Soviets, including vital messages that helped the Red Army prepare for the Battle of Kursk in 1943. Even after transferring to MI6 in 1944, Cairncross continued to pass information to the Soviets, and after the war, he may have given them plans for the new NATO alliance.
1 Britannica Source
1. John Cairncross
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What impact did John Cairncross’s actions have on World War II and the postwar period?
John Cairncross, a British civil servant and member of the Cambridge spy ring, significantly aided the Soviet Union during World War II by passing along vital intelligence. As a German translator at Bletchley Park, he smuggled decrypted German communications to the Soviets, including information that helped the Red Army prepare for the Battle of Kursk in 1943. After the war, he may have passed NATO plans to the Soviets. Exposed in 1951, he resigned but later confessed to espionage in 1964. His actions provided critical support to the Soviet war effort, though he maintained he never betrayed British interests.
1 Britannica Source
1. John Cairncross
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

John Cairncross (born July 25, 1913, Lesmahagow, Scotland—died October 8, 1995, Herefordshire, England) was a British literary scholar and civil servant who was identified in the 1990s as the “fifth man” in the notorious Cambridge spy ring that included Kim Philby, Guy Burgess, Donald Maclean, and Anthony Blunt.

The son of an ironmonger and a schoolteacher, Cairncross graduated from the University of Glasgow in 1933 with a degree in German and French. He studied modern languages at the Sorbonne in Paris and then at Trinity College, Cambridge. At Cambridge he frequented left-wing circles and met other members of the future spy ring, but he did not fit in with the polished young men and pursued his future careers apart from them.

Cairncross entered the Foreign Office in 1936, having passed the entrance examinations with outstanding marks. Shortly after, he was introduced by James Klugmann, a communist from Cambridge, to a Soviet agent who invited him to aid the antifascist movement. Cairncross was transferred in 1938 to the Treasury and in 1940, after the start of World War II, to the Cabinet Office, where he became the private secretary of Sir Maurice Hankey, the chancellor of the Duchy of Lancaster. In this latter capacity Cairncross may have passed to the Soviets a copy of the MAUD report, which evaluated Britain’s prospects for building an atomic bomb.

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Pop Quiz: 17 Things to Know About World War II

In 1942 he was assigned as a German translator to Bletchley Park, a government research centre north of London where encrypted German military communications were decoded and disseminated to intelligence services. Cairncross smuggled many decrypted German communiqués to the Soviets, including vital messages on army movements on the Eastern Front that helped the Red Army to prepare for the Germans’ huge tank offensive at the Battle of Kursk (July–August 1943).

Cairncross transferred in 1944 to MI6, Britain’s foreign intelligence agency, where for a time he worked under Philby. In 1945 he returned to the Treasury. After the war he may have passed plans for the new NATO alliance to the Soviets. In 1951, after Maclean and Burgess had fled England to escape investigation, notes written by Cairncross were found in Burgess’s home, and Cairncross was interrogated by MI5, the British domestic security agency. He denied having spied for the Soviets, but he agreed to resign from the Civil Service.

Cairncross began a new career as a literary scholar, teaching in the United States at Northwestern University in Illinois and at Case Western Reserve University in Ohio. Over the following decades he published a number of translations and studies of the great French playwrights Racine, Corneille, and Molière, as well as a history of Christian attitudes toward polygamy, After Polygamy Was Made a Sin (1974).

In 1964, after Philby had defected to the Soviet Union, Cairncross was again interrogated by MI5, and this time he confessed to espionage. British authorities decided not to prosecute him, perhaps in exchange for receiving information from Cairncross, and both sides agreed to remain silent on his past. Cairncross continued his literary studies and writing and also worked for the United Nations Food and Agriculture Organization in Rome. In 1990 and 1995 he was named as the “fifth man” in books by two former Soviet intelligence officers. Cairncross moved back to England and prepared his memoirs, which were published after his death as The Enigma Spy (1997). Cairncross insisted to the last that he had never betrayed secrets that damaged Britain, and he was not ashamed to admit that he had given the Soviet Union information it used to win its great victory at the Battle of Kursk.

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