Now, through a series of decisions it is decided that the Western Allies will use chemical weapons from D-Day onwards. This is justified in public by exposition of German cruelties (pick your favorite, there's plenty of them). The second, private argument by Churchill is that the inevitable German counter-strikes will delay Soviets.
So, what will be the effect if chemical weapons will be used against front-line troops? IMHO, the effect on Germans will be quite devastating due to Allied air superiority and dependence upon horses.