(Taken from CBC Archives: http://archives.cbc.ca/IDC-1-71-2425-14165/conflict_war/firstworldwar/)

• On April 24, 1915 the Germans used chlorine gas against the Canadian First Division at the Second Battle of Ypres. With the wind in the German’s favour, anything short of a full retreat would have put the Canadians in the path of the gas. Realizing the only fresh air was at the German line, the Canadians pushed forward, breathing through water- or urine-soaked rags as makeshift gas masks. (It was believed that the ammonia in the urine would neutralize the chlorine.)

• The Canadians held their ground until they were reinforced by British troops a day and a half later. The battle earned the Canadian forces great respect, though it came at a cost of some 6,000 men, and ended in a stalemate.