It was formed on August 15, 1914 following Britain’s declaration of war on the German Empire, with an initial strength of one infantry division.

The CEF and corps was eventually expanded to four infantry divisions, which were all committed to the fighting in France and Belgium along the Western Front.

[3] Popular support for the war was found mainly in English Canada, especially among those born in the United Kingdom who had recently emigrated.

The artillery and engineering units underwent significant re-organization as the war progressed, in keeping with rapidly changing technological and tactical requirements.

The unit embarked for Europe in May 1916 at Toronto, but were held at Aldershot, Nova Scotia, due to objections by the US government, causing a number of desertions and resignations.

The battalion finally arrived in England in September, having officially dropped the "American Legion" title,[11] although the term continued to be used informally throughout the war.

On returning to New York after the war, 2,754 US citizens who had fought with British Empire forces, including 300 African Americans, were detained on Long Island and New Jersey because they lacked the correct documentation.

The plight of these men was covered extensively in local and national media, and following several days of negotiations and bureaucratic wrangling, those who had returned legally were allowed to enter the country.

[12] A United States Department of War report in early 1918 estimated that 25,000 to 30,000 Americans were serving in the Canadian Expeditionary Force.

They had previously experienced the effects of shellfire and participated in aggressive trench raiding despite a lack of formal training and generally inferior equipment.

The Germans employed chlorine gas to create a hole in the French lines adjacent to the Canadian force and poured troops into the gap.

For three days, Canadian and reinforcing British units fought to contain the penetration with a series of counter-attacks while using handkerchiefs soaked in urine to neutralize effects of the gas.

The toll of the five-month campaign cannot be statistically verified by a single reliable source, however historians have estimated German losses at roughly 670,000 and an Allied total of 623,907.

[20] The Canadian Corps suffered almost 25,000 casualties in this the final phase of the operation, but like the remainder of the BEF, it had developed significant experience in the use of infantry and artillery and in tactical doctrine, preparation and leadership under fire.

The Corps, led by Lieutenant General Arthur Currie, captured Hill 70 overlooking Lens and forced the Germans to launch more than twenty counter-attacks in attempting to remove the threat to its flank.

The Ypres offensive began with the swift capture of the Messines Ridge, but weather, concrete defences and the lack of any other concurrent Allied effort meant that the BEF fought a muddy, bloody campaign against the main German force for two months.

With the situation in Italy and with the French army deteriorating, it was decided to continue the push and Currie was ordered to bring in the Canadian Corps.

[21] Since they were mostly unmolested by the German Army's offensive manoeuvres in the spring of 1918, the Canadians were ordered to spearhead the last campaigns of the War from the Battle of Amiens on August 8, 1918 to the winning of a tacit victory for the Allies, when the armistice came into effect on November 11, 1918.

Beginning in 1918, in anticipation of the disbandment of the Canadian Expeditionary Force, plans for the re-organization of the militia were initiated, guided largely by the deliberations of the Otter Commission, convened for this purpose.

[24][25] In the later stages of the European war, particularly after their success at Vimy Ridge and Passchendaele, the Canadian Corps was regarded by friend and foe alike as one of the most effective Allied military formations on the Western Front.

[28] About 150 soldiers of an un-named battalion attacked the police station at Prince Albert in 1917, in protest of the imposition of strict liquor laws.

[29] A.A. Milne's well-known character "Winnie-the-pooh" is derived from a black bear taken to Europe as the mascot of a western Canadian army unit during the war.

[30] Besides mounted and cavalry units, the Canadian Expeditionary Force used horses, mules, donkeys and cattle to transport gun pieces on the battle front, as motorized vehicles could not handle rough terrain.