Assuming the British have exited the war in 1940 and the Germans opt to use gas against the Soviets, how does the Eastern front play out?
I'm looking to discuss this scenario specifically, so would we avoid discussing how the British exit the war?
Without the threat of British retaliating with gas and anthrax on German cities, the Germans opt to use their gas stocks on the Soviets during their invasion.
Nerve gas though is not available in quantities until September 1942, which is when the first batch of the major new Tabun production facility would reach the front line (the factory went online in June). Still the Germans have about 20-25 tons of Tabun available in June 1941 and the capacity to make 1-1.5 tons a month until June of 1942. Sarin wasn't available until 1944 due to its difficulty of production, and then only about 50 tons a year could be produced.
They also have a massive chemical engineering industry that dwarves the Soviet's production capabilities and potential. The Soviets also don't have a domestic source of rubber and rely on Buna (synthetic rubber), so don't have enough gas masks for their troops. In fact in June 1941 there is a massive deficit of masks with front line troops, leaving them massively vulnerable to WW1 era gasses. No only that but their masks aren't meant to protect against tear and vomiting gas, which the Germans often used to force wearers to pull of their masks and leave them vulnerable to poison gases.
So assuming the Germans use gas rockets, artillery shells, and aircraft bombs during the Eastern Front campaign, what happens?
I assume the aircraft bomb version would be the most practical in the fast moving battles of Barbarossa, but when the artillery catches up in the big pocket battles they will play a role as well.
The important places to use gas would probably be in pocket reduction, strong point clearing (including beachheads that the Soviets were very hard to remove from), and city fighting like at Stalingrad. IMHO the Germans would end up taking less losses as a result of these early battles due to the Soviet pockets being disrupted by the use of gas. I could see Tabun being used during the Kiev pocket, basically being saved up for when it would be most useful. During the winter gas cannot vaporize, so would be useless for those battles.
At Stalingrad gas would be critical not only as a means of clearing out the city, but also for surpressing/eliminating artillery across the Volga. About this time Tabun would be available in major amounts too, so it could be used regularly and the Soviets wouldn't have the capability to defend against it with.
Kursk, if something like it still happens despite butterflies, would also see heavy saturation of nerve gas, but would it be a game changer? How about the rest of the fighting on the Eastern front?