U.S. chemical weapons program

The United States chemical weapons program began in 1917 during World War I with the creation of the U.S. Army's Gas Service Section and ended 73 years later in 1990 with the country's practical adoption of the Chemical Weapons Convention (signed 1993; entered into force, 1997). Destruction of stockpiled chemical weapons began in 1985 and is still ongoing. Alleged use of chemical agents by the U.S. in the Korean (1950–53) and Vietnam (1955-1975) conflicts has never been substantiated and there is no reliable evidence that the country ever used chemical weapons on either battlefield. The U.S. Army Medical Research Institute of Chemical Defense (USAMRICD), at Aberdeen Proving Ground, Maryland, continues to operate.

The U.S. had participated in the formulations of the Hague Conventions of 1899 and 1907 which banned chemical warfare, among other things, but the U.S. never joined the article which prohibited chemical weapons.

In World War I, the U.S. established its own chemical weapons research facility and produced its own chemical munitions. It produced 5,770 metric tons of these weapons, including 1,400 metric tons of phosgene and 175 metric tons of mustard gas. This was about 4% of the total chemical weapons produced for that war and only just over 1% of the era's most effective weapon, mustard gas. (U.S. troops suffered less than 6% of gas casualties.) The U.S. also established the First Gas Regiment, which left Washington, D.C. on Christmas Day, 1917, and arrived at the front in May 1918. During its time in France, the First Gas Regiment used phosgene in a number of attacks.

The United States began large-scale production of an improved vesicant gas known as Lewisite, for use in an offensive planned for early 1919. Lewisite was a major American contribution to the chemical weapon arsenal of World War I, although it was not actually used in the field during World War I. It was developed by Captain Winford Lee Lewis of the U.S. Chemical Warfare Service in 1917. (The Germans later claimed that they had manufactured it in 1917 prior to the American discovery.) By the time of the armistice on 11 November 1918, a plant near Willoughby, Ohio, was producing 10 tons per day of the substance, for a total of about 150 tons. It is uncertain what effect this new chemical agent would have had on the battlefield, however, as it degrades in moist conditions.

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