Mustard gas was mainly used by Germany on the British and Canadian soldiers and later against the French army. The allies didn't use the agent until they seized a stockpile of mustard gas shells from Germany. Mustard gas was disposed as an aerosol giving the air a yellow brown look. It also had a distinct smell. Soldiers wearing gas masks were not protected from absorbing it through their skin. Mustard gas can remain on the ground for days and weeks.