30 July 1929 Commissioned Lieutenant RAMC on probation. He was confirmed in rank in February 1930.
1930–1936 Served in India.
30 Jan 1933 Promoted Captain RAMC.
Feb 1936 Captain J G Black was appointed Divisional Adjutant 43rd (Wessex) Division vice Major John Egerton Rea who vacated the post on 1 February 1936.
June 1938 Captain J G Black was appointed Deputy Assistant Directors of Medical Services 43rd (Wessex) Division.
30 July 1939 Promoted Major RAMC.
1939–1940 Served with the British Expeditionary Force France.
10 Feb 1941 Acting Lieutenant Colonel RAMC.
1941–1943 Commanding Officer 9 Field Ambulance.
1943–1946 Assistant Director of Medical Services HQ Commando Group.
1944–1945 Assistant Director of Medical Services North West Europe.
22 June 1945 Acting Colonel L/RAMC.
22 Dec 1945 War Substantive Lieutenant Colonel L/RAMC.
22 Dec 1945–29 May 1946 Temporary Colonel.
17 July 1946 Major (War Substantive Lt Col) J G Black was promoted Lieutenant Colonel RAMC.
1946 Assistant Director of Hygiene HQ Land Force Greece. Specialist in Hygiene.
1946–1947 Assistant Director of Hygiene HQ Cairo District.
1947–1949 Assistant Director of Hygiene HQ British Troops Egypt.
1949–1950 Deputy Director of Army Health HQ Western Command.
19 Aug 1949–20 Apr 1950 Temporary Colonel.
1950–1951 Army School of Health.
1951–1952 Serving with the British Army of the Rhine (BAOR).
29 Nov 1951 Promoted Colonel L/RAMC.
1951 Commanding Officer 22 Field Ambulance.
1951–1952 HQ British Troops Berlin.
1953–1955 Assistant Director of Medical Services HQ Singapore Base District Far East Land Force.
1955–1957 Assistant Director of Medical Services HQ Highland District.
1958 Assistant Director of Medical Services HQ London District.
21 Nov 1958–15 June 1960 Temporary Brigadier.
1958–1960 Deputy Director of Medical Services HQ 1 British Corps BAOR.
Malta 22 June 1960 Deputy Director of Medical Services Malta.
Malta 18 Oct 1961 Left for England.
18 Nov 1961 Retired on retired pay and was granted the honorary rank of Brigadier.
26 Sept 1963 Colonel (Honorary Brigadier) J G Black ceased to belong to the Regular Army Reserve of Officers having attained the age limit of recall, but retained the honorary rank of Brigadier.