Born in New Zealand and educated at Napier Boys' High School,[1] McGregor joined the Royal Air Force in 1928.

He served as a pilot but in 1931 he attended the Aircraft Engineering Course and he subsequently undertook several engineering-related tours.

33 Squadron at Heliopolis in Egypt and on attachment at Lydda in Palestine, where he earned the Distinguished Service Order for his leadership during policing duties.

2 Group in 1951 before being appointed Director of Guided Missile Development at the Ministry of Supply in 1953.

[2] He went on to be Assistant Controller, Aircraft at the Ministry of Supply in 1956, Chief of Staff (Air Defence) at Headquarters SHAPE in 1957 and Commander-in-Chief of Fighter Command in 1959.