Actually Zyklon B came out of WWI research, and in the interim it was licensed worldwide for use as a fumigating agent. Including from 1929 onwards in the Unit

Actually Zyklon B came out of WWI research, and in the interim it was licensed worldwide for use as a fumigating agent. Including from 1929 onwards in the United States, where it was used by the Public Health Service to fumigate freight trains and clothes of Mexican immigrants entering the country.