 Coates was appointed Commandant of the Royal Military College, Duntroon in 1983 and Head of the Defence Staff in Washington, D.C. in 1984; he was appointed an Officer of the Order of Australia in 1987 in recognition of his service there.He was appointed Assistant Chief of the Defence Force (Policy) in 1987 and appointed Chief of the General Staff in 1990; he was appointed a Companion of the Order of Australia in 1992 in recognition of his service to the Australian Army, particularly in that role.In retirement he wrote a number of books about the Australian Army and Australian military history.