The Department of National Defence was created in 1923 by the National Defence Act which established one civil department in place of the previous Department of Militia and Defence, the Department of the Naval Service and the Air Board. The Canadian Forces Reorganization Act in 1968 unified the Royal Canadian Navy, the Canadian Army and the Royal Canadian Air Force into a single service called the Canadian Armed Forces. The Department is responsible for the control and management of the Canadian Armed Forces, and all matters related to national defence establishments and the defence of Canada.

The 31st Canadian Infantry Battalion (Alberta) was organized in Calgary on March 15, 1915, and came to a strength of 1,033. In the First World War it served in France and Belgium with the 6th Infantry Brigade, 2nd Canadian Division from September 18, 1915 until the armistice.