Poison gas would be most effective piped onto the beaches on D-Day. Chemical warfare favours defenders, because they won't sweat to death running around in protective clothing.
Commonwealth soldiers waded ashore laden with gas masks, gas capes, etc. As soon as the learned that Germans were not deploying chemical weapons, WALLY soldiers discarded excess equipment. Road-side ditches were littered with gas masks, but Commonwealth troops kept their gas capes because they were handy as rain ponchoes, etc.
Commonwealth soldiers waded ashore laden with gas masks, gas capes, etc. As soon as the learned that Germans were not deploying chemical weapons, WALLY soldiers discarded excess equipment. Road-side ditches were littered with gas masks, but Commonwealth troops kept their gas capes because they were handy as rain ponchoes, etc.