John Robert Fisher Jeffreys (25 January 1916 – 13 January 1944) was a British

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, mathematical structure, structure, space, Mathematica ...

and

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

codebreaker. Jeffreys was educated at

Brentwood School, Essex Brentwood School is a Selective school, selective, independent school (UK), independent day school, day and boarding school in Brentwood, Essex, Brentwood, Essex, England in the Public School (United Kingdom), public school tradition. The scho ...

, and

Downing College, Cambridge Downing College is a constituent college of the University of Cambridge and currently has around 950 students. Founded in 1800, it was the only college to be added to the university between 1596 and 1869, and is often described as the oldest of ...

, where he graduated as a Wrangler in Part II of the mathematics

tripos TRIPOS (''TRIvial Portable Operating System'') is a computer operating system. Development started in 1976 at the Computer Laboratory of Cambridge University and it was headed by Dr. Martin Richards. The first version appeared in January 1978 a ...

in 1936. Appointed a

research fellow A research fellow is an academic research position at a university or a similar research institution, usually for academic staff or faculty members. A research fellow may act either as an independent investigator or under the supervision of a p ...

at Downing, he joined the

codebreaking Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic secu ...

efforts at

Bletchley Park Bletchley Park is an English country house and Bletchley Park estate, estate in Bletchley, Milton Keynes (Buckinghamshire), that became the principal centre of Allies of World War II, Allied World War II cryptography, code-breaking during the S ...

in September 1939 alongside fellow Cambridge mathematicians

Gordon Welchman William Gordon Welchman OBE (15 June 1906 – 8 October 1985) was an English mathematician. During World War II, he worked at Britain's secret decryption centre at Bletchley Park, where he was one of the most important contributors. In 1948, a ...

, with whom he had previously worked closely, and

Alan Turing Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher and theoretical biologist. He was highly influential in the development of theoretical computer ...

. These three, together with Peter Twinn and working under

Dilly Knox Alfred Dillwyn "Dilly" Knox, CMG (23 July 1884 – 27 February 1943) was an English classics scholar and papyrologist at King's College, Cambridge and a codebreaker. As a member of the Room 40 codebreaking unit he helped decrypt the Zimme ...

, formed the research section working on the German

Enigma machine The Enigma machine is a cipher device developed and used in the early- to mid-20th century to protect commercial, diplomatic, and military communication. It was employed extensively by Nazi Germany during World War II, in all branches of the W ...

, 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 Cryptanalysis of the Enigma ciphering system enabled the western Allies of World War II, Allies in World War II to read substantial amounts of Morse code, Morse-coded radio communications of the Axis powers that had been enciphered using Enigm ...

, a task which took over three months, completed on 7 January 1940.Ralph Erskine, "The Poles Reveal their Secrets: Alastair Denniston's Account of the July 1939 Meeting at Pyry", pp. 294-305, ''Cryptologia'' 30(4), December 2006 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.Ralph Erskine, "Breaking Air Force and Army Enigma", p. 53 in ''Action this Day'', edited by Ralph Erskine and Michael Smith, 2001 In early 1940, a section called "

Hut 6 Hut 6 was a wartime section of the Government Code and Cypher School at Bletchley Park, Buckinghamshire, Britain, tasked with the solution of German Army and Air Force Enigma machine cyphers. Hut 8, by contrast, attacked Naval Enigma. Hut 6 w ...

" — 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,Gordon Welchman, ''The Hut Six Story'', p. 125 Jeffreys took a vacation, but became ill and was diagnosed with

tuberculosis Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by ''Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can al ...

and

diabetes Diabetes mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained high blood sugar levels. Diabetes is due to either the pancreas not producing enough of the hormone insulin, or the cells of th ...

.Gordon Welchman, ''The Hut Six Story'', p. 103 He died in January 1944. Gordon Welchman later recalled:

References

Sources

* Updated and extended version of ''Action This Day: From Breaking of the Enigma Code to the Birth of the Modern Computer'' Bantam Press 2001 {{DEFAULTSORT:Jeffreys, John 20th-century British mathematicians Bletchley Park people Alumni of Downing College, Cambridge Fellows of Downing College, Cambridge 1916 births 1944 deaths 20th-century deaths from tuberculosis Tuberculosis deaths in the United Kingdom Deaths from diabetes in the United Kingdom