Combat efficiency is much reduced when using gas mask.
Moreover, while gas masks for horses do (did) exist, good luck persuading your horse wearing it. And horses were rather crucial in WWI and still very important in WWII.
We did not see gas used during WWII mostly because of Hitler’s aversion and a (mistaken) belief that the Allies had stockpiles of nerve agents and Germany feared their retaliation.
Chemical warfare was only effective the first couple times it was used, i.e., before people invented the gas mask.
Combat efficiency is much reduced when using gas mask.
Moreover, while gas masks for horses do (did) exist, good luck persuading your horse wearing it. And horses were rather crucial in WWI and still very important in WWII.
We did not see gas used during WWII mostly because of Hitler’s aversion and a (mistaken) belief that the Allies had stockpiles of nerve agents and Germany feared their retaliation.
My impression is that chemical weapons were very effective in the Iran-Iraq war (e.g.), despite the gas mask having been invented.