The 3rd Brigade landed in St Nazaire, France on February 15, 1915. The 15th Battalion disembarked from the SS Mount Temple and entrained that evening for their move to The Front. Over the course of the year the battalion would spend several months in France, but the majority of its time would be spent in Belgium at locations in the infamous Ypres salient.
February and March were spent in France first with a British battalion near Armentieres for familiarization followed by front line trench tours near Fromelles and Neve Chapelle. The battalion moved to Belgium in early April and took up front line positions forward of Gravenstafel ridge across the Stroombeck and in the town of St Julien on April 20th for what would become the battalion’s baptism of fire. During the battle of 2nd Ypres (fought between 22-26 April), the battalion was essentially decimated during the chlorine gas attack against the Canadian positions on April 24th suffering the highest single day casualties of any Canadian unit during the war.
Quickly rebuilt with the reserve company from England and large numbers of reinforcements principally from the 17th and 30th Battalions, the battalion fought again in May at Festubert and did trench tours at Givenchy and Bethune. In June the battalion returned to the Ypres salient where it would remain for the balance of the year mainly in the Ploegsteert, Hill 63 and Messines Road areas.