[4] During the Second World War, his cousin Edward Anthony Calnan was killed in action while serving with the Queen's Own Rifles of Canada.
Parachuting, winter exercises in Fort Churchill, and attendance at the Subalterns Long Course at Royal Military College in 1954 preceded his promotion to Lieutenant in July 1955.
Upon promotion, he was posted to HQ RCA, 1 Canadian Infantry Division in Petawawa as Staff Learner, Royal Artillery and participated in the first divisional exercises to be held in the new Camp Gagetown.
In 1957, he attended the Long Technical Gunnery Course at RCSA and in September 1957, was posted to A Battery, 1 RCHA as a Gun Position Officer (GPO) for B Troop in Winnipeg.
In September 1974, he was promoted to colonel[10] and in November, attended French language training until appointed Base Commander of CFB Shilo in July 1975.
Calnan received permission from the Department of National Defence to run in the 1982 Ontario municipal elections for the office of Councillor in Rideau Township while still serving on active duty in the military.
In conjunction with a business partner, Colonel Calnan purchased and developed a 64-hectare plot of land that they named Fairmile Estates[15] located at the corner of McCordick Road and Donnelly Drive south of North Gower, Ontario.
Born and raised a Roman Catholic, Colonel Calnan volunteered to act as the Chairman of the Building Committee in 1980 for the construction of Saint Leonard's church in Manotick.
[17] Calnan was also a member of the Royal Canadian Legion and served on the Executive Committee of South Carleton Branch #314 from 1980 to 1997 including five terms as President.