19 Oct 1946 Emergency Commission Lieutenant RAMC.
1946–1949 Served with the Middle East Land Force.
19 Oct 1947 Captain RAMC.
12 July 1948 Short Service Commission Captain RAMC.
12 June 1951 Permanent Regular Army Commission Captain RAMC.
1952 Junior Specialist in Pathology.
19 Oct 1954 Major RAMC.
1954–1957 Medical Liaison Officer The Atomic Energy Research Establishment Harwell.
1955 Senior Specialist in Pathology.
1957–1959 Assistant Director of Pathology British Military Hospital Nicosia, and BMH Dhekelia Cyprus.
Malta 1959 Served at The David Bruce Military Hospital Mtarfa.
Malta 1960 Served at The David Bruce Military Hospital Mtarfa.
1960–1963 Worked at the Chemical Defence Experimental Establishment Porton.
19 Oct 1961 Lieutenant Colonel RAMC.
1963–1965 Assistant Director of Pathology Eastern Command.
1963 Consultant Pathologist.
1965 Assistant Director General Army Medical Services MOD (AMD8).
31 Mar 1978 Major–General James Cooper Crook, MD, FRCPath, DTMH was appointed Honorary Physician to The Queen in succession to Brigadier William Semple Millar, retired.
31 Mar 1986 Relinquished his appointment as Honorary Colonel 380 Blood Supply Unit, Royal Army Medical Corps (Volunteers), tenure expired.