The SS tests Zyklon B
September 3, 1941
The first gassings of prisoners occur in Auschwitz I. The SS tests Zyklon B View This Term in the Glossary gas by killing 600 Soviet prisoners of war and 250 other ill or weak prisoners. Testing takes place in a makeshift gas chamber in the cellar of Block 11 in Auschwitz I. Zyklon B was the commercial name for crystalline hydrogen cyanide gas, manufactured by I.G. Farben and normally used as an insecticide. The "success" of these experiments will lead to the adoption of Zyklon B as the killing agent for the yet-to-be-constructed Auschwitz-Birkenau killing center.
https://encyclopedia.ushmm.org/content/en/article/auschwitz-key-dates