Charles Manville developed this weapon in the 1930s as a riot control tool, and they were built in 12ga, 25mm, and 37mm. We should point out that the 12ga version was for tear gas rounds only (like today's 12ga flare launchers) and not safe to use with high-pressure ammunition. Anyway, it was intended for use by prison guards and riot police, offering a much greater ammunition capacity than any other contemporary launcher. During World War II, Manville tried to sell the military on a high-pressure version to fire 37mm explosive rounds, but was unsuccessful. Instead, the Manville company spent the was making parts for the Oerlikon 20mm AA guns, and the tooling for the gas launcher was all destroyed. http://www.forgottenweapons.com/other-handguns/manville-gas-gun/