OBITUARY - Leslie Yoxall

The Times
October 27, 2005

OBITUARY - Leslie Yoxall
------------------------
May 18, 1914 - September 30, 2005

Mathematician who helped to break wartime German Enigma codes at Bletchley 
Park

LESLIE YOXALL was one of the elite group of cryptanalysts who broke the 
German Enigma cipher at Bletchley Park during the Second World War.

Leslie Yoxall was born in Salford in 1914, the youngest of four brothers 
whose father died young in a tramway accident. He went to the Manchester 
Grammar School, and in 1933 went up as a mathematics scholar to Sidney 
Sussex College, Cambridge. He was a wrangler, with a distinction in part 
III, and gained his PhD in 1941.

On the outbreak of the war, he had returned to Manchester Grammar as a 
mathematics teacher, but not for long. Gordon Welchman, a Sidney Sussex 
mathematics don, had been preparing for code-breaking work at Bletchley 
Park when the war was seen to be inevitable, and he quickly recruited his 
ablest mathematics colleagues, Yoxall among them. After interviews with 
Alan Turing and Hugh Alexander, he joined the team working on German naval 
Enigma in Hut 8 at Bletchley Park in April 1941.

At that time the naval Enigma was being solved by a combination of cribs 
and banburismus (a combinatorial attack on the indicator system). Yoxall 
joined the shift-working banburismus section. Sometimes a message 
contained a highly sensitive section that had been pre-enciphered using 
keys only available to officers. These were announced as "only for 
officers" with an indicator. Often one or two of these were broken by 
cribbing, leaving others about which Hut 8 knew only the wheel settings 
but not the pluggings. Yoxall devised and demonstrated an important 
technique, known in gratitude as yoxallismus, which often led to the 
recovery of the pluggings and the decipherment of the sensitive messages.

In 1942, when the decryption of the naval Enigma was automated, Yoxall 
moved to Hut 7 to work on a Japanese naval cipher in support of the US 
effort, and there he made a significant contribution by identifying how 
the permutations were constructed.

After the war he spent some time at Eastcote writing up the work, and in 
1953 moved to Cheltenham with what had become GCHQ, where he had a long 
and distinguished career.

He was posted to Washington as a liaison officer, 1959-63, and had an 
unprecedented second tour there in 1968-72.

Steeped in mathematics and its teaching, Yoxall was a Fellow of the 
Institute of Mathematics and its Applications, and a member of the 
Mathematical Association and the Association of Teachers of 
Mathematics..../snip/


...On his retirement from GCHQ in the mid-1970s he returned to the 
teaching career which the war had interrupted in 1941, offering 
mathematics tuition and coaching to would-be scholars at school and 
university. His success at this over some score of years earned him the 
admiration and gratitude of a multitude of pupils and their families.

Leslie Yoxall was married in 1949 to Doris Gibson of Kesh, Co Fermanagh. 
Together they worked indefatigably for the harmony of Anglo-American 
relations in Cheltenham and Washington. She died in 2002. They had no 
children.

Leslie Yoxall, wartime codebreaker and schoolmaster, was born on May 18, 
1914. He died on September 30, 2005, aged 91. 


http://www.timesonline.co.uk/article/0,,60-1844435,00.html



                                                \--=-//
                                                ( o^o )
 ---------------------------------------oOOO------(_)---OOOo-----
|      Martin Postranecky        Phone : [00-44]-(0)20-7679 3453 |
|  Senior Experimental Officer   Phone : [00-44]-(0)20-7679 2000 |
|   UNIVERSITY COLLEGE LONDON    Fax :   [00-44]-(0)20-7679 7145 |
| DEPT.OF PHYSICS AND ASTRONOMY  E-Mail: [email protected]        |
| Gower Street,London, WC1E 6BT  http://www.hep.ucl.ac.uk/       |
 ---------------------------------------------ooOo-----oOo-------