In the early 1950's, the U.S. began producing Sarin for use in artillery shells and rockets. For a time, it partnered with Shell, the gas company, to manufacture and stockpile the weapons at the Army's Rocky Mountain Arsenal in Colorado.
(Those weapons include the "Honest John" warhead shown above, containing dozens of bomblets that each contained about a pound of Sarin.)
"Shell produced dichlor for the Army," according to an official military historical account. "The Army used dichlor in an intermediate process in the manufacture of GB nerve agent."
When Syria lost its main ally, Egypt, to Israel in a 1979 peace deal, the Alawite-controlled government in Damascus set out to regain its military edge by establishing a secret chemical weapons program that required the involvement of Western companies -- whether they knew it or not.