The Second Battle of Ypres took place from April 22 to May 25, 1915, during World War I. It was notable for being the first major battle where chemical weapons, specifically chlorine gas, were used on the battlefield. The battle occurred in the Ypres Salient in Belgium, where the Allied Forces, primarily the British Empire, faced the German Army. The use of gas caused panic and confusion among the Allied troops, leading to significant casualties. Despite initial German advances, the Allies managed to hold much of their ground. The battle highlighted the horrors of modern warfare and the need for improved protective measures against chemical attacks.