As a minister of war he insisted on using "poisonous gas" against revolting tribes in India in 1919. His later advocates insist that he meant use of tear gas, but nevertheless, the India Office refused.

He also encouraged the Air Marshal Trenchard to experiment with mustard gas against Mesopotamian rebels, but that never came to nothing. He honestly thought that Mesopotamia really wasn't worth an expensive, proper bombing...

Where he succeeded, was using gas against Soviet troops in Russia, of all places. Porton Down, of all places, had developed a new gas, DM, that was then tested against Russians in Murmansk-Archangel. It's decapacitating "vomit gas", now internationally banned.