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- John_R.F._Jeffreys abstract "John Robert Fisher Jeffreys (25 January 1916 – 13 January 1944) was a British mathematician and World War II codebreaker. A research fellow at Downing College, Cambridge, Jeffreys joined the codebreaking efforts at Bletchley Park in September 1939 alongside fellow Cambridge mathematicians Gordon Welchman, with whom he had previously worked closely, and Alan Turing. These three, together with Peter Twinn and working under Dilly Knox, formed the research section working on the German Enigma machine, and were housed in \"The Cottage\" at Bletchley Park.Jeffreys was put in charge of a small section manufacturing perforated sheets for use in the cryptanalysis of the Enigma, a task which took over three months, completed on 7 January 1940. One type were the Zygalski sheets, known as Netz at Bletchley Park, a technique revealed to the British by Polish cryptologists. Another type, named \"Jeffreys sheets\", were different, and were a \"catalogue of the effect of any two Enigma rotors and the reflector\". Jeffreys's perforated sheets were used by Polish cryptologists in exile in France to make the first wartime decryption of an Enigma message on 17 January 1940.In early 1940, a section called \"Hut 6\" — named after the building in which it was initially housed — was created to work on solving German Army and Air Force Enigma messages. Jeffreys was chosen to run the hut alongside Welchman. Jeffreys was in charge of \"Sheet-Stacking and Machine Room activities\", while Welchman handled \"Registration, Intercept Control, Decoding, and relations with the intelligence people in Hut 3\".In May 1940, Jeffreys took a vacation, but became ill and was diagnosed with tuberculosis and diabetes. He died in January 1944. Gordon Welchman later recalled:\"Jeffreys was very much liked at Bletchley Park. His death was a tragic loss to all of us. We felt deep sympathy for his fianceé, Pat Hempsted, who had been a member of his team from its beginnings in the Cottage. She was involved both in the initial punching of the sheets and in the testing of drops on which our early breaks depended.\"↑ ↑ ↑ ↑ ↑ ↑ 6.0 6.1 ↑ ↑ ↑ ↑ ↑ 11.0 11.1".
- John_R.F._Jeffreys birthDate "1916-01-25".
- John_R.F._Jeffreys birthYear "1916".
- John_R.F._Jeffreys deathDate "1944-01-13".
- John_R.F._Jeffreys deathYear "1944".
- John_R.F._Jeffreys thumbnail Zygalski_sheets_(perforated_sheets).jpg?width=300.
- John_R.F._Jeffreys wikiPageID "8315517".
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- John_R.F._Jeffreys wikiPageOutDegree "24".
- John_R.F._Jeffreys wikiPageRevisionID "676215380".
- John_R.F._Jeffreys wikiPageWikiLink Alan_Turing.
- John_R.F._Jeffreys wikiPageWikiLink Bletchley_Park.
- John_R.F._Jeffreys wikiPageWikiLink Category:1916_births.
- John_R.F._Jeffreys wikiPageWikiLink Category:1944_deaths.
- John_R.F._Jeffreys wikiPageWikiLink Category:20th-century_British_mathematicians.
- John_R.F._Jeffreys wikiPageWikiLink Category:Fellows_of_Downing_College,_Cambridge.
- John_R.F._Jeffreys wikiPageWikiLink Category:People_associated_with_Bletchley_Park.
- John_R.F._Jeffreys wikiPageWikiLink Cryptanalysis.
- John_R.F._Jeffreys wikiPageWikiLink Cryptanalysis_of_the_Enigma.
- John_R.F._Jeffreys wikiPageWikiLink Diabetes_mellitus.
- John_R.F._Jeffreys wikiPageWikiLink Dilly_Knox.
- John_R.F._Jeffreys wikiPageWikiLink Downing_College,_Cambridge.
- John_R.F._Jeffreys wikiPageWikiLink Enigma_machine.
- John_R.F._Jeffreys wikiPageWikiLink Gordon_Welchman.
- John_R.F._Jeffreys wikiPageWikiLink Hut_6.
- John_R.F._Jeffreys wikiPageWikiLink Mathematician.
- John_R.F._Jeffreys wikiPageWikiLink Peter_Twinn.
- John_R.F._Jeffreys wikiPageWikiLink Research_fellow.
- John_R.F._Jeffreys wikiPageWikiLink Tuberculosis.
- John_R.F._Jeffreys wikiPageWikiLink United_Kingdom.
- John_R.F._Jeffreys wikiPageWikiLink World_War_II.
- John_R.F._Jeffreys wikiPageWikiLink Zygalski_sheets.
- John_R.F._Jeffreys wikiPageWikiLink File:Zygalski_sheets_(perforated_sheets).jpg.
- John_R.F._Jeffreys wikiPageWikiLinkText "Jeffreys, John R.F.".
- John_R.F._Jeffreys wikiPageWikiLinkText "John Jeffreys".
- John_R.F._Jeffreys wikiPageWikiLinkText "John R.F. Jeffreys".
- John_R.F._Jeffreys dateOfBirth "1916-01-25".
- John_R.F._Jeffreys dateOfDeath "1944-01-13".
- John_R.F._Jeffreys name "Jeffreys, John".
- John_R.F._Jeffreys placeOfBirth "Barnet, Middlesex, UK".
- John_R.F._Jeffreys placeOfDeath "Bovey Tracey, Devonshire, UK".
- John_R.F._Jeffreys shortDescription "British mathematician".
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- John_R.F._Jeffreys description "British mathematician".
- John_R.F._Jeffreys description "British mathematician".
- John_R.F._Jeffreys subject Category:1916_births.
- John_R.F._Jeffreys subject Category:1944_deaths.
- John_R.F._Jeffreys subject Category:20th-century_British_mathematicians.
- John_R.F._Jeffreys subject Category:Fellows_of_Downing_College,_Cambridge.
- John_R.F._Jeffreys subject Category:People_associated_with_Bletchley_Park.
- John_R.F._Jeffreys hypernym Mathematician.
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- John_R.F._Jeffreys comment "John Robert Fisher Jeffreys (25 January 1916 – 13 January 1944) was a British mathematician and World War II codebreaker. A research fellow at Downing College, Cambridge, Jeffreys joined the codebreaking efforts at Bletchley Park in September 1939 alongside fellow Cambridge mathematicians Gordon Welchman, with whom he had previously worked closely, and Alan Turing.".
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- John_R.F._Jeffreys depiction Zygalski_sheets_(perforated_sheets).jpg.
- John_R.F._Jeffreys givenName "John".
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- John_R.F._Jeffreys name "Jeffreys, John".
- John_R.F._Jeffreys name "John Jeffreys".
- John_R.F._Jeffreys surname "Jeffreys".