The 1st Division spent the winter of 1914–15 training in England, and were sent to France in . After a period of indoctrination about the realities of trench warfare, they took control of a section of trench in the Ypres Salient on 17 April 1915. Only five days later, the Germans used poison gas for the first time on the Western Front, sending clouds of chlorine wafting over the Allied trenches. French colonial troops on the Canadians' left flank broke, leaving an enormous hole in the Allied line.