I don't know offhand of any case where the U.S. intentionally used chemical weapons other than in testing or WWI. However, while a herbicide, Agent Orange could be classified as a chemical weapon due to the aftereffects now known. Granted it wasn't used as a chemical weapon per se, but it had virtually the same effects over time (years) and that was on our own troops as well.

http://www.fas.org/nuke/guide/usa/cbw/cw.htm

(I'd forgotten about chlorine gas)


>>So, you claim that US had NEVER used chemical weapons?
>>
>
>It is possible that we used mustard gas or some other blistering gas during world war one (it was common at the time).
>
>Other than that, yes.