Leslie Yoxall
Encyclopedia
Albert Leslie Yoxall was a British codebreaker at Bletchley Park
during World War II
. He devised a method to assist in solving Enigma
messages which was dubbed Yoxallismus. After the war he worked at GCHQ until the mid-1970s.
accident. Leslie Yoxall was educated at Manchester Grammar School
from 1925 and Sidney Sussex College, Cambridge
from 1933, graduating with first-class honours. He received his doctorate in 1941.
On the outbreak of war, Yoxall returned to teach at Manchester Grammar School
, and was next in line to become the head of mathematics.
wrote to Yoxall advising him that he would soon be asked to help with "war work". In due course, Yoxall was invited to join Bletchley Park and was, alongside Bill Tutte, interviewed by Hugh Alexander
and then Alan Turing
. Yoxall was selected to join the team in Hut 8
, working on Naval Enigma as a "temporary junior administrative officer". He worked on the problem of Offizier (Officer) messages, which had been enciphered on Enigma with a second setting for additional security. Yoxall discovered what became known as "Yoxallismus", a method for recovering the Offizier setting.
In October/November 1942, he moved to Hut 7 to work on a Japanese naval cipher, making a significant contribution in identifying how the cipher permutations were constructed.
and then moved again with GCHQ to Cheltenham
in 1953. He worked in Washington as a liaison officer from 1959 to 1963, and returned again in 1968 to 1972. After the first tour in the US, a letter sent to the director of GCHQ (Clive Loehnis
) stated that "his superior technical competence and analytic insight have served as a stimulus to everyone with whom he came into contact. His engaging personality, diplomacy and tact have endeared him to us all".
He retired from GCHQ around 1974 and returned to teaching, tutoring and coaching students in mathematics.
Bletchley Park
Bletchley Park is an estate located in the town of Bletchley, in Buckinghamshire, England, which currently houses the National Museum of Computing...
during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. He devised a method to assist in solving Enigma
Enigma machine
An Enigma machine is any of a family of related electro-mechanical rotor cipher machines used for the encryption and decryption of secret messages. Enigma was invented by German engineer Arthur Scherbius at the end of World War I...
messages which was dubbed Yoxallismus. After the war he worked at GCHQ until the mid-1970s.
Early life
Yoxall was born in Salford, and was the youngest out of four brothers. His father died young in a tramwayRail transport
Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...
accident. Leslie Yoxall was educated at Manchester Grammar School
Manchester Grammar School
The Manchester Grammar School is the largest independent day school for boys in the UK . It is based in Manchester, England...
from 1925 and Sidney Sussex College, Cambridge
University of Cambridge
The University of Cambridge is a public research university located in Cambridge, United Kingdom. It is the second-oldest university in both the United Kingdom and the English-speaking world , and the seventh-oldest globally...
from 1933, graduating with first-class honours. He received his doctorate in 1941.
On the outbreak of war, Yoxall returned to teach at Manchester Grammar School
Manchester Grammar School
The Manchester Grammar School is the largest independent day school for boys in the UK . It is based in Manchester, England...
, and was next in line to become the head of mathematics.
Codebreaking at Bletchley Park
In April 1941, Gordon WelchmanGordon Welchman
Gordon Welchman was a British-American mathematician, university professor, World War II codebreaker at Bletchley Park, and author.-Education and early career:...
wrote to Yoxall advising him that he would soon be asked to help with "war work". In due course, Yoxall was invited to join Bletchley Park and was, alongside Bill Tutte, interviewed by Hugh Alexander
Conel Hugh O'Donel Alexander
Conel Hugh O'Donel Alexander, CMG, CBE was an Irish-born British cryptanalyst, chess player, and chess writer. He worked on the German Enigma machine at Bletchley Park during World War II, and was later the head of the cryptanalysis division at GCHQ for over 20 years...
and then Alan Turing
Alan Turing
Alan Mathison Turing, OBE, FRS , was an English mathematician, logician, cryptanalyst, and computer scientist. He was highly influential in the development of computer science, providing a formalisation of the concepts of "algorithm" and "computation" with the Turing machine, which played a...
. Yoxall was selected to join the team in Hut 8
Hut 8
Hut 8 was a section at Bletchley Park tasked with solving German naval Enigma messages. The section was led initially by Alan Turing...
, working on Naval Enigma as a "temporary junior administrative officer". He worked on the problem of Offizier (Officer) messages, which had been enciphered on Enigma with a second setting for additional security. Yoxall discovered what became known as "Yoxallismus", a method for recovering the Offizier setting.
In October/November 1942, he moved to Hut 7 to work on a Japanese naval cipher, making a significant contribution in identifying how the cipher permutations were constructed.
Post-war work
After the war he moved to EastcoteEastcote
Eastcote is a suburban area established around an old village in Greater London, and is part of the London Borough of Hillingdon.In the Middle Ages, Eastcote was one of the three areas that made up the parish of Ruislip, under the name of Ascot...
and then moved again with GCHQ to Cheltenham
Cheltenham
Cheltenham , also known as Cheltenham Spa, is a large spa town and borough in Gloucestershire, on the edge of the Cotswolds in the South-West region of England. It is the home of the flagship race of British steeplechase horse racing, the Gold Cup, the main event of the Cheltenham Festival held...
in 1953. He worked in Washington as a liaison officer from 1959 to 1963, and returned again in 1968 to 1972. After the first tour in the US, a letter sent to the director of GCHQ (Clive Loehnis
Clive Loehnis
Sir Clive Loehnis KCMG is a former director of the British signals intelligence agency, GCHQ, a post he held from 1960 to 1964.-Career:Loehnis was born in 1902 in Chelsea, London...
) stated that "his superior technical competence and analytic insight have served as a stimulus to everyone with whom he came into contact. His engaging personality, diplomacy and tact have endeared him to us all".
He retired from GCHQ around 1974 and returned to teaching, tutoring and coaching students in mathematics.