Per https://en.wikipedia.org/wiki/History_of_chemical_warfare#Wo... this (a) overlooks the widespread use of chemical weapons in the Pacific theater, and (b) ascribes the non-use by Germany to humanitarian reasons, which is largely speculative. Actual quotes from officers discuss far more practical reasons: Germany feared chemical retaliation, and the horses relied upon for logistics could not be outfitted with sufficiently performant gas masks.