At the end of his third year at Cambridge, Strachey suffered a nervous breakdown, possibly related to coming to terms with his homosexuality.

An application for a research degree at the University of Cambridge was rejected and Strachey continued to work at STC throughout the Second World War.

After the war he fulfilled a long-standing ambition by becoming a schoolmaster at St Edmund's School, Canterbury, teaching mathematics and physics.

In his spare time, Strachey developed a preliminary version of a program for the game of draughts ("checkers" in American English) in May 1951.

[8] When Strachey heard about the Manchester Mark 1, which had a much bigger memory, he asked his former fellow-student Alan Turing for the manual and transcribed his program into the operation codes of that machine by around October 1951.

Researchers at the University of Canterbury, Christchurch restored the acetate master disc in 2016 and the results may be heard on SoundCloud.

[14] In May 1952, Strachey gave a two-part talk on "the study of control in animals and machines" ("cybernetics") for the BBC Home Service's Science Survey programme.

While working on the St. Lawrence Seaway project, he was able to visit several computer centres in the United States and catalogue their instruction sets.

[17][18] He filed a patent application in February that year and gave a paper "Time Sharing in Large Fast Computers" at the inaugural UNESCO Information Processing Conference in Paris where he passed the concept on to J. C. R.

In 1973, Strachey (along with Robert Milne) began to write an essay submitted to the Adams Prize competition, after which they continued work to revising it into book form.

[22] Strachey contracted an illness diagnosed as jaundice which, after a period of seeming recovery, returned and he died of infectious hepatitis on 18 May 1975.

[23] After his death, Strachey was succeeded by Sir Tony Hoare as Head of the Programming Research Group at Oxford, starting in 1977.