When was chlorine first used in World War 1?

Chlorine was first used as a chemical weapon in World War I by the German army on April 22, 1915, during the Second Battle of Ypres. This marked the first large-scale use of chemical warfare in the conflict, leading to devastating effects on soldiers and prompting a shift in warfare tactics. The introduction of chlorine gas signaled the beginning of a brutal era of chemical warfare that would continue throughout the war.