College celebrate life of former Mathematics head and World War II code breaker

Professor Rees completed his undergraduate studies at Sidney Sussex College, Cambridge, where he was supervised by the British-American mathematician, Gordon Welchman. Inspired by the lectures of Phillip Hall, Rees began his postgraduate studies in September 1939, exploring a complex branch of algebra known as semigroup theory. This research was interrupted, however, by the onset of the Second World War, and Rees was soon recruited by his former mentor, Gordon Welchman, to join a team of code breakers at Hut 6, a wartime section of the Government Code and Cypher School (GC&CS) at Bletchley Park. It was there, in May 1940, that David and fellow Cambridge recruits deployed the ‘Herival tip’ to break German army and air force Enigma Ciphers. The ‘Herival tip’, named after one of Rees’ fellow Cambridge students, is now recognised as one of the most significant discoveries of the Second World War.

Following his wartime stint at Bletchley Park, Rees accepted a teaching post at Manchester University, an emerging centre of computer development, before returning to Cambridge as a fellow of Downing College. In 1958, David took up the chair of Applied Mathematics at Exeter where he worked alongside his wife, Joan, who rose through the ranks to become Senior Lecturer. As head of Mathematics and Mathematical Sciences, Rees carried out his duties with care and diligence and despite an increasingly heavy administrative workload, was elected a fellow of the Royal Society in 1968.

Joan survived her husband by less than two weeks. David and Joan are survived by four daughters, two of whom hold chairs of mathematics at other British universities. David and his daughter, Mary, a specialist in complex dynamic systems at Liverpool University, are the only father-daughter pair to have achieved election as fellows to the Royal Society.