What is called the second battle of Ypres began with a bombardment of the little city on April 20, 1915. The rain of shells continued on through April 22, 1915, on the evening of which the British artillery observers reported a strange green vapor moving over the French trenches. The wind was blowing steadily from the northeast. Soon the French troops were staggering back from the front, blinded and choking from the deadly German gas. Many of their comrades had been unable to leave the spot where they were overtaken by the fumes. Those who fled in terror rushed madly across the canal, choking the road to Vlamertinghe. A part of the Zouaves and Turcos ran south toward the Langemarck road, finally reaching the reserve battalions of the Canadians. Ere long the Canadians caught the deadly odor also.
But the work of the gas did a much more valuable thing for the German troops than causing the agonizing death of many hundreds and sending thousands in headlong flight. It made a four-mile-wide opening in the front of the Allies. And the Germans were quick to take advantage of that opening. They followed the gas, and were aided in their advance by artillery fire. The French were forced back on the canal from Steenstraate to Boesinghe. The Canadians had not suffered so much from the gas as the French soldiers, but their flank was too exposed for them to do much effective work against the onrushing Teutons. The attempt to rally the Turcos failed. The Third Brigade could not withstand the attack of four divisions, and was forced inward from a point south of Poelcappelle until its left rested on the wood east of St. Julien. There was a gap beyond it, and the Germans were forcing their way around its flank. Because the entire First Brigade of Canadians had been held in reserve it could not be brought up in time to save the situation. Two of the battalions, the Sixteenth and Tenth, were in the gap by midnight. They charged and recovered the northern edge, and the guns of the Second London Division, which had been supporting the French in the wood east of St. Julien. But the British could not hold all they retook, and were forced to abandon the guns because the artillery horses were miles away. So parts of the guns were made useless before the Germans had them again.