During his military career, he rose to the rank of colonel and was appointed to the Order of the British Empire as an Officer (OBE).

Annan's publications include Leslie Stephen (1951)—awarded the James Tait Black Memorial Prize, Roxburgh of Stowe (1965), Our Age (1990), described by Professor John Gray in the New Statesman as a "marvellous compendium of the higher gossip", Changing Enemies (1995), and The Dons (1999).

[3] In October 1940, he entered officer cadet training, and in January 1941 was commissioned in the Intelligence Corps and posted to MI14, a department of the War Office, where "Annan was given an important job in operational intelligence studying the movement by rail of German forces".

[2] In 1942, he was posted to the Joint Intelligence Staff in the War Cabinet Office, which was located with Winston Churchill in his bunker.

(See Patrick Higgins, Heterosexual Dictatorship: Male Homosexuality in Post-War Britain, London: Fourth Estate Ltd; 1996, p. 125.)