On 22 April 1915, elements of the German Fourth Army attacked the northern shoulder of the Ypres Salient, a strategically vital position defended by British, Canadian, French and Belgian forces. There, for the first time on the Western Front, the German Army employed chlorine gas, a lethal chemical agent. Lacking any protection against the suffocating chlorine, French troops defending the sector between the Yser Canal and Poelkapelle were overrun and forced to withdraw towards Ypres. As British and Canadian reinforcements fought to secure the break in the Allied line, German forces launched a second gas attack on the morning of 24 April. The gas cloud was concentrated against positions defended by the 2nd and 3rd Canadian Infantry Brigades of the 1st Canadian Division along the northern slope of Gravenstafel Ridge near the Stroombeek. Nos. 1, 3, and 4 Companies of the 15th Battalion (48th Highlanders of Canada), engulfed by the heaviest concentration of gas and artillery fire, were devastated by the German assault. Elements of these companies, as well as the Battalion’s forward headquarters and support position near the Steenakker windmill continued to fight for several more hours until finally being overrun, captured, or forced to withdraw that morning. A number of survivors were able to retire to a key secondary defensive position known as Locality C. At the same time, the Battalion’s No. 2 Company was heavily engaged in the defence of St Julien, about one mile west of this site. Although the Germans later succeeded in capturing St. Julien and Locality C, they failed either to reach Ypres or to eliminate the salient surrounding the town which had been the main objective of the Fourth Army offensive. The Allied forces suffered grievously high casualties defending Ypres in April and May of 1915. The heroic, stubborn, and often desperate defence of the salient resulted in the 1st Canadian Division incurring approximately 6,000 casualties. During the gas attack of 24 April, the 15th Battalion sustained 647 casualties, more than any other Canadian battalion.
The Second Battle of Ypres, 22-26 April 1915, was the first major engagement of the war for the units of the 1st Canadian Division. The Canadians played a key role in the costly but successful defence of the Ypres salient. Although almost destroyed, the 15th Battalion (48th Highlanders of Canada) survived, rebuilt, and fought in all the major battles in which the 1st Canadian Division was engaged for the duration of the Great War.