The hidden date for this stamp can be found on one of the maple leaves along the left edge of the stamp.
During the early days of the Second World War Canadian Postal authorities believed that the stamps in use since 1938 should be replaced with a new issue featuring Canada's substantial contribution to war work. A new general issue to last for the duration of the hostilities was designed. Subjects depicting Canada's munitions, war supplies, shipbuilding, agriculture, her importance as a great air-training centre, and as a source of food were chosen for the pictorial stamps.
Interior of a Canadian munitions factory, showing a 25-pound gun being inspected. Modern war required the total mobilization of economic forces to equip and supply armaments to the fighting forces. For Canada this implied that in addition to providing men and materials for her own fighting forces, she must, to the maximum of her ability, furnish her allies with munitions. The scene illustrates the change of Canada's factories from a peacetime to a wartime basis.