Poison gas, introduced by the Germans early in 1915 and thereafter used by both sides, killed thousands and left thousands disabled. It was “improved” as the war went on, chlorine being succeeded by phosgene and phosgene by mustard, but it never produced or even contributed significantly to a major victory on any front. Its deficiencies came to be so universally recognized that not even the Nazis would use it in World War II.
