Conel Hugh O’Donel Alexander, CMG, CBE (19 April 1909 – 15 February 1974) 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. In chess, he was twice British chess champion and earned the title of International Master. He was usually referred to as C. H. O’D. Alexander in print and Hugh in person.
In February 1940 Alexander arrived at Bletchley Park, the British codebreaking centre during World War II. He joined Hut 6, the section tasked with breaking German Army and Air Force Enigma messages. In 1941, he transferred to Hut 8, the corresponding hut working on Naval Enigma. He became deputy head of Hut 8 under Alan Turing. Alexander was more involved with the day-to-day operations of the hut than Turing, and, while Turing was visiting the United States, Alexander formally became the head of Hut 8 around November 1942. Other senior colleagues included Stuart Milner-Barry, Gordon Welchman, and Harry Golombek. In October 1944, Alexander was transferred to work on the Japanese JN-25 code.
In mid-1946, Alexander joined GCHQ (under the control of the Foreign Office), which was the post-war successor organisation to the Government Code and Cypher School (GCCS) at Bletchley Park. By 1949, he had been promoted to the head of “Section H” (cryptanalysis), a post he retained until his retirement in 1971.
MI5’s Peter Wright, in his 1987 best-selling book Spycatcher: The Candid Autobiography of a Senior Intelligence Officer, wrote about Alexander’s assistance to MI5 in the ongoing Venona project, as well as other important mutual cooperation between the two organizations, which broke down previous barriers to progress. “Any help is gratefully received in this department”, Alexander told Wright, and that proved the case from then on. Wright also lauded Alexander’s professionalism, and opined that the exceptional mental demands of his cryptanalytical career and chess hobby likely contributed to Alexander’s early death at age 64, despite his healthy lifestyle.