The Second Battle of Ypres was, in fact, a series of four engagements. Initially planned by the Germans as a local tactical battle to reinforce their lines near Ypres, their introduction of gas on the battlefield in the west for the first time significantly impacted the battles for the remainder of the war.

The battle commenced late in the afternoon of April 22nd. German troops released chlorine gas over a front being held by French colonial troops. The French were unprepared for the attack, and 6,000 troops in the path of the gas quickly became casualties. This created a substantial gap in the allied lines. However, the German were unable to fully exploit that gap due to troop shortages and the effective defense of the Canadian troops positioned on the flanks.

The attacks had caused the line to retreat behind the village of St Julien, which subsequently became the focal point of the battle. On April 24th, the Germans once again attacked with gas, this time targeting the Canadian troops. The troops had learned that covering their faces with something soaked in urine could partially mitigate the effects of the gas. Despite this, the gas still created a large gap in the Allied lines. However, the Germans were unable to attack through the gas, and by the time the gas had dispersed, Canadian and British troops were able to reoccupy the positions they held previously.

The third attack occurred on May 8th on a strategic ridge known as the Frezenberg Ridge. The German had advanced field artillery forward to facilitate the attack and commenced it with a heavy bombardment of the Canadian and British lines. Following the artillery bombardment, the Germans launched their assault. The initial two waves were repelled by the remaining Allied troops, but their third assault succeeded in breaching the lines, creating a 2-mile gap. However, a valiant counterattack by the Princess Patricia’s Canadian Light Infantry halted the German assault and stabilized the line.
The fourth attack occurred on May 24th when the Germans launched another assault with poison gas. The defenders once again attempted to halt the German advance, but they were once again overwhelmed. By the end of the day, the lines had been pushed back over a mile.

As with all battles on the Western Front, the outcome was relatively unchanged. The Germans managed to advance a few miles and compressed the Ypres Salient, bringing the allied lines closer to the city. The city of Ypres was virtually destroyed. German casualties were recorded as 34,933 for the battles, while British casualties were 59,279, French casualties were 21,973, and Canadian casualties were another 5,975.