Adolf Hitler experienced the effects of mustard gas use during World War I and was a twice and highly-decorated war hero. He abhorred, as did Franklin Roosevelt, the idea of using poison gas during warfare. Of the "great leaders", only Churchill (a drunk) and Stalin (a convicted criminal) rubbed their hands in glee over such prospects. Stalin didn't have the means and Churchill was opposed by the British Cabinet, at least, in part. Churchill, forever the war's most eloquent liar, described in a statement his desire, and vision, of Germans dying by the thousands in city after city. He wanted to "anthrax" the entire European continent but had to be satisfied with only a tiny island off the coast of Scotland for experimental purposes. Today, that island is still uninhabitable.
The proposed "gassing" of Iwo Jima was stopped cold by F.D.R. who also blocked a proposal for using poison gas against Japan proper. Hitler, in spite of recommendations, and insistence, from Hermann Goering, Robert Ley, and Martin Bormann, listened but never signaled approval. One could rightly wonder why those terrible Nazis, who were manufacturing TABUN, another nerve gas, by the tons, would stoop in atypical German-fashion, to using the insecticide ZYKLON-B to inefficiently "exterminate" hapless jews.
Chemically, TABUN is known as dimethyl-aminoethoxyl-cyanophosphine oxide. It is ten times more deadly than SARIN. Dr. Gerhard Schrader was also responsible for its development which was successful in the summer of 1939. Under the direction of Hermann Ochsner, a plant for its production was established in west Poland, that is, near the city of Dyhernfurth in Silesia. This was also the region where Soviet troops raped, mostly unto death, every German female from the age of 6 upwards (even elderly women in wheelchairs and the pregnant), during their "liberation" activities at the end of the war.