After suffering heavy losses of their own officers, the British called upon trained officers from the Canadian Army to fill their own ranks in the field.  Rex eagerly volunteered for the program, having been in the Canadian Officer Training Corps since 1942.  He was an only child and educated, leaving the University of New Brunswick for engineering after a year to join the service.

On June 29, 1944, at the age of 20, he was given command of No. 1 Platoon, the machine gun platoon of A Company, 2d Battalion, Middlesex Regiment.  At the time, the regiment was near Cambes Wood in the beach head of the British 3d infantry Division.  As one of two CANLOAN replacements to the regiment, he got to know the unit that had suffered losses since the invasion on June 6.  Becoming cordial so quickly was well noted by Brigadier Weston, who noted that Cockney soldiers, quicker witted than most English troops, heed powers of personality and leadership and when these qualities are not apparent, they can be the hardest troops to become acquainted with.

From day one, they gladly accepted Rex into their ranks, and he remunerated them with stoic and distinguished leadership.  He was recommended for the Military Cross, but due to the strict nature of rationing awards, he was instead granted a commendation for gallantry from Field Marshall Montgomery.  

Two months after joining the unit, his carrier rolled over a double teller mine - two mines stacked on one another so they explode simultaneously - and the he was thrown several yards up the road as the steel of the carrier peeled back exposing the cabin.  One man was immediately blown in half, the others survived without wounds, but all were quite dazed.  Rex was taken to the field hospital with some splinters and gravel in his legs, bruises throughout his body, and a busted ear drum.  He managed to return to his platoon on August 24 and fought through Holland and Germany to complete the campaign in Northwest Europe.  His service in World War II began his career as a Canadian officer and he remembered his time as a CANLOAN officer with pride and as a highlight of his service.

He finished his schooling when he graduated from the Royal Military College and joined the Royal Canadian Electrical and Mechanical Engineers, a suitable branch for Rex as their motto was Arte et Marte - by skill and by fighting.  In Korea, he was mentioned in dispatches for service as second in command with the No. 191 Infantry Workshop and subsequently the No. 23 Infantry Workshop that replaced the former.  For three months he was officer in charge of the No. 170 Light Aid Detachment to the 1st Royal Canadian Horse Artillery, moving him from relative safety in a rear echelon position to up on the line servicing weapons and equipment in the trenches and bunkers lining Korean hills.  He was highly skilled, knew the .303 Vickers Machine Gun with his eyes closed, and had already been tested under fire.

He was a staff officer at National Defense Headquarters in Ottawa and Deputy Secretary-General of the International Commission for Supervision and Control in Vietnam in 1967.  He retired in 1975 as a Lieutenant Colonel. An avid outdoorsman, Rex was an accomplished target shooter and won the King's Medal in 1948 for top shot in the Canadian Forces. He was three times a member of Canada's National shooting team at competitions at Bisley, England, once as commandant of the Cadet corps as seen in the images below.