The nerve agent Tabun was first of 3 nerve gases the Germans produced in WW2 but did not use. Tabun was discovered in 1936, accepted by the military in 1937, trials began in 1939, while the main production facility was being built from Jan 1940 onwards and ran by I.G. Farben. Production began in 1942 and produced anywhere from 15,000-30,000 tons (the Wiki Soviet reported 12,500 tons is incorrect as it comes from the last stock at the facility that produced it and not counting the stocks sent to 2 other underground facilities for storage nor the shipment to Falkenhagen where N-Material was stored). It is often claimed that Hitler did not order the use of Tabun in artillery or bomb form due to his own gassing in WW1. That is most likely a myth b/c a barge of 150mm Tabun shells was found on the Oder River by the Red Army ready for use in 1945. The problem with using the artillery rounds were that they were in 150mm caliber for use with med-heavy field artillery. Berlin had mostly AAA 88mm-128mm guns and lower caliber infantry howitzers up to 105mm. The Luftwaffe also had no experience with loading nerve agents for aerial bombs nor tactics in the air if they encountered escorts while carrying the lethal gas- so whatever stocks were around just sat idle. There are also reports that Hitler considered using the gas but that in the chaos of 1945 the orders never came through. Tabun is also remembered as the preferred gas that Speer said he plotted to use against Hitler and the bunker through the air ventilation shaft. He was thwarted as a tall, reinforced chimney was built around it, putting it out of reach! The Waffen SS would have never allowed Speer to get that close anyway with a suspicious canister...