One significant scientific advancement that influenced the course of World War I was the development of chemical weapons, particularly chlorine and mustard gas. These substances were first used extensively during the war, changing the nature of combat. Chemical warfare introduced new psychological and physical horrors, as soldiers faced not only traditional artillery and infantry but also invisible, toxic gases that could incapacitate or kill within minutes. The deployment of such weapons led to dire health consequences for soldiers and civilians alike and ultimately ushered in international agreements seeking to regulate or ban chemical weapons in subsequent conflicts.