[1] Humphrey joined the Royal Air Force College Cranwell in January 1939[2] and was granted a permanent commission as a pilot officer on 30 April 1940.

[5] On a single night in May 1941, he shot down one bomber and two other enemy aircraft near the Dutch coast: he was awarded the Distinguished Flying Cross for this on 30 May 1941.

[2] Awarded the Air Force Cross on 1 January 1943,[8] he attended the Low Attack Instructor's School at RAF Milfield in early 1943.

[2] He was awarded a Bar to the Air Force Cross on 1 January 1945,[10] and promoted to the war substantive rank of squadron leader on 20 February 1945.

[2] Having been appointed an Officer of the Order of the British Empire in the 1951 New Year Honours[14] and promoted to wing commander on 1 July 1951,[15] he became a senior instructor there in February 1953.

[2] In December 1953, Humphrey piloted "Aries IV", a Canberra B.2, from Cape Town to London in a then record 13 hours 16 minutes and 25 seconds.

[16] Humphrey attended RAF Staff College in 1955 and was awarded a second Bar to his Air Force Cross in the 1955 Birthday Honours.

[19] Humphrey became Officer Commanding RAF Akrotiri in February 1959 and then attended the Imperial Defence College in 1962[2] before being promoted to air commodore on 1 July 1962.

[31] Following promotion to Marshal of the Royal Air Force on 6 August 1976,[32] Humphrey was appointed Chief of the Defence Staff on 24 October 1976.