A passage in Otto skorzeny's "My Commando Operations" tells of Soviet threats to use gas unless the Germans stopped using some sort of oxygen/liquid oxygen related ordinance in the Moscow sector circa 1941. I've never been able to determine the veracity of Skorzeny's statement, or what sort of weapon he might have been referring to.
Churchill was REAL lucky Hitler didn’t call his bluff. He was still in the age of mustard gas and phosgene. Hitler had Tabun and Sarin nerve gas [still the silver, if not gold, standard today.
It was probably one of the reasons the Allies hushed up that little incident in Italy in 1943.