Rod served with the Calgary Highlanders Militia from 1948 to 1950.
He enrolled with 2PPCLI as a Lieutenant in September 1950. He served as a Platoon Commander during the Korean War until he was wounded in action on 7 March, 1951 during the assault on Hill 532. He served as Liaison Officer for 27 and 28 British Commonwealth Brigades, then as an Assistant Adjutant when 2 PPCLI reverted to command of 25 Canadian Infantry Brigade.
Major Middleton returned to Canada for Parachute training in September 1951 and served at the Airborne School and Offensive Air Support School at Canadian Joint Air Training Centre at Rivers Manitoba from 1952 to 1958 when he was posted to 1 PPCLI Victoria where he served as Second in Command A Company. He was then appointed Adjutant in June 1960, a position he held until May 1963 when he proceeded to the Defence Services Staff College in Wellington, India.
On Graduation in December 1963 he was appointed General Staff Officer Grade 2 Special Operations in the Directorate of Military Training at Army Headquarters in Ottawa, serving there until August 1965 when he attended the United States Armed Forces Staff College in Norfolk Virginia. On Graduation in January 1966 he joined 2 PPCLI in Edmonton during which time he commanded the last Army Junior NCO School in Wainwright.
In May 1966 he proceeded to Germany where he was appointed OC Headquarters Company and Battalion Operations Officer 1 PPCLI, and maintained that appointment following rotation with 2 PPCLI until July 1967, when he was appointed General Staff Officer 2 Tactical Air Operations at the Joint Warfare establishment at Old Sarum, England.
In August 1969 he returned to Canadian Forces Headquarters in Ottawa and was appointed Staff Officer 2 in the Special Warfare Section of the Directorate of Land Operational Readiness, serving for a period of time as Staff Coordinator to the former Colonel of the Regiment, Col W.B. Sutherland.
In March 1973, Major Middleton was posted as Senior Staff Officer Southern Alberta Militia District in Calgary until retirement in July 1975.