[4] During the Second World War he transferred to 4th County of London Yeomanry, winning the Military Cross as a captain and temporary major for his actions on 19 and 23 November during Operation Crusader in the Western Desert.
[11] Onslow continued in part-time service with the Territorial Army after the war, now with 3rd/4th County of London Yeomanry (Sharpshooters), and was promoted to substantive lieutenant-colonel on 1 May 1947.
[15] He was appointed Captain of the Yeomen of the Guard on 5 November 1951,[16] and Honorary Colonel of 3rd/4th County of London Yeomanry (Sharpshooters) on 21 June 1956.
[17] As Captain of the Yeomen of the Guard he took part in the funeral of King George VI,[18] and the coronation of Queen Elizabeth II.
They had two children: Onslow divorced his wife in 1962 and remarried, to Nina Edith Jo Sturdee (who died in 2006), later that year.