What gas was first used in Ypres?

The first gas used in Ypres during World War I was chlorine gas. It was deployed by the German army on April 22, 1915, marking one of the first large-scale uses of chemical warfare in history. The attack caused panic and confusion among Allied troops and led to significant casualties. Chlorine gas was particularly effective because it was colorless and had a pungent odor, making it difficult for soldiers to prepare for its effects.