During the night 18-19 July 1944, 2 Canadian Corps made an assault crossing of the River Orne. This operation was one of the most important of the entire campaign, and its failure would have had a serious effect on the whole operation in Normandy. As part of the Corps plan, the 31st Field Company, the Corps of Royal Canadian Engineers, had the task of constructing a bridge over the River Orne at Caen to allow the passage of the so necessary supporting arms. Failure, therefore, to complete construction of this bridge would have had serious effects on the army plan. Major McCallum was in command of this operation and though harassed by mortar and sniper fire, and by enemy planes, carried on with the task and brought it to a very successful conclusion. His courage, leadership and ability were of the highest order and undoubtedly contributed largely to the success of the operation.
Douglas McCallum was born in Carberry, MB but grew in Quebec. He was a sales engineer living in Ottawa prior to the war.
Tragically, killed in a mortar attack on the Orne River on 25 July 1944. He is buried in the Bretteville-sur-Laize Canadian War Cemetery in France. The province of Manitoba honoured Major McCallum by naming Lake McCallum in his honour.