Early on the morning of 22 April 1915, a thick greenish cloud swirled and drifted toward the Allied lines near Ypres, Belgium. As the chlorine gas permeated the forward trenches, Algerian colonial troops and French regulars fled in chaos from the ghastly effects of the gas. (The chlorine combined with moisture in the breathing passages and lungs to form a highly corrosive acid.) The attack created a gaping hole in the Allied front. The Canadian Corps commander, Lieutenant-General Edwin Alderson, redeployed the 1st Canadian Division to fill it.
The troops of the 3rd Brigade, commanded by Brigadier-General Richard Turner, hastily improvised gas masks made from urine-soaked handkerchiefs and repulsed the initial German attacks. On 24 April, Second Canadian Contingent Embarks for Europe: Jan.-May 1915. Brigadier-General Arthur Currie's 2nd Brigade bore the brunt of the German offensive and doggedly resisted repeated attempts to break through the Allied lines. Despite experiencing terrible casualties, the 1st Canadian Division held against the German onslaught. Out of the original complement of 10,000 men, 6,035 Canadians were killed or wounded.