taken from cbc archives on april 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 men and ended in a stalemate