Wouldn't work, bongs had mass produced gas masks and had gas mask drills pretty early on, even though they had no knowledge of nerve gas they were expecting a shitshow.

Gas however would have been effective in hot humid conditions, like the Pacific islands or Burma where soldiers needed exposed skin to prevent heat exhaustion and were tempted to avoid using the masks. Perhaps Greece also since the valleys tend to pool gas, it would have been hellish trying to approach their bunkers, even if they had been bombed open by the Luftwaffe, the Germans would have had to prepare to sustain much higher casualties and for the war to be drawn out, delaying Operation Barbarossa even longer.