Oliver StracheyCBE (3 November 1874 – 14 May 1960), a Britishcivil servant in theForeign Office, was acryptographer fromWorld War I toWorld War II.

Strachey was a son of SirRichard Strachey,colonial administrator andJane Maria Strachey, writer andsuffragist, and a brother of the writerLytton Strachey, the writerDorothy Bussy and the psychoanalyst and editor of theStandard EditionJames Strachey. He was educated atEton College; he attendedBalliol College, Oxford for one term (Hilary 1893). His parents sent him on a tour around the world withRobert Bridges.^{[citation needed]} Then he studied the piano in Vienna underTheodor Leschetizky. While there he attended the funeral ofJohannes Brahms in 1897.^[1] His playing was of a certain standard, but not up to concert performance, so he returned to England and joined theForeign Office.^[1]

His first marriage, in 1900, to Ruby Julia Mayer^[2] produced one daughter,Julia Strachey, and ended in divorce.

In 1911, he marriedRay Costelloe (1887–1940). They had two children,Barbara Strachey (born 1912) andChristopher Strachey (born 1916). Christopher Strachey later became a pioneer in the development of computers and computer languages. Barbara Strachey became a writer.

While at the Foreign Office, he engaged in work on theEast Indian Railway and historical research. He co-authored with his wife Ray a work onKeigwin's Rebellion (1683–84), an episode in the history ofBombay; it was published in 1916.

In World War I, he was in British Military (Army) Intelligence,MI1. Between the wars, he was in theGovernment Code and Cypher School. In 1934, Strachey andHugh Foss broke the Japanese naval attaché machine cipher.

In World War II, he was atBletchley Park. He headed the ISOS section deciphering various messages on theAbwehr network involved with turned German agents (part of theDouble Cross system), with the first decrypt issued on 14 April 1940. Initially codenamed Pear, the decrypts became known as ISOS, standing for Illicit Services (Oliver Strachey). He was replaced as head of ISOS byDenys Page in early 1942.

In December 1941, Strachey went to Ottawa, Canada, where he was chief cryptographer in theExamination Unit. This ambiguously named, top secret cypher department was the Canadian equivalent of Bletchley Park. His predecessor at the Unit was the notoriousHerbert Osborne Yardley, who in 1931 had published a sensational exposé of American and British cryptography in World War I,The American Black Chamber.^[3] Yardley's contract was not renewed under pressure from Washington. Strachey refused to go to Ottawa until Yardley had left the city.

Strachey brought with him from England, keys to high-level FrenchVichy and Japanese diplomatic codes, which initiated close cooperation with Washington and London. Although he did not speak or read Japanese, he helped break the Japanese encryption, which was very complex, since it used variations ofkanji,hiragana, andromanization. He returned to Bletchley Park in September 1942.^[4]

His recreations were music and reading. He was appointed aCommander of the Order of the British Empire (CBE) in 1943.

• Who Was Who, 1951–1960.
• Action this Day, edited by Michael Smith & Ralph Erskine (2001, Bantam London).ISBN 0-593-04910-1.
• A History of the Examination Unit 1941–1945, edited by G. deB. Robinson, the official history written in 1945, is in Library and Archives Canada.
• "Crytptographic Innocence: The Origin of Signals Intelligence in Canada in the Second World War", by Wesley Wark, inJournal of Contemporary History, October 1987.