Brandt and Bouhler developed plans to expand the programme of euthanasia to adults . In July 1939 they held a meeting attended by Conti and Professor Werner Heyde , head of the SS medical department . This meeting agreed to arrange a national register of all institutionalised people with mental illnesses or physical disabilities . The first adults with disabilities to be killed en masse by the Nazi regime were Poles . After the invasion on 1 September 1939 , adults with disabilities were shot by the SS men of '' Einsatzkommando '' 16 , '' Selbstschutz '' and EK - '' Einmann '' under the command of SS - '' Sturmbannführer '' Rudolf Tröger , with overall command by Reinhard Heydrich , during the genocidal Operation Tannenberg . All hospitals and mental asylums of the Wartheland were emptied . The region was incorporated into Germany and earmarked for resettlement by '' Volksdeutsche '' following the German conquest of Poland . In the Danzig ( now Gdańsk ) area , some 7,000 Polish patients of various institutions were shot and 10,000 were killed in the Gdynia area . Similar measures were taken in other areas of Poland destined for incorporation into Germany . The first experiments with the gassing of patients were conducted in October 1939 at Fort VII in Posen ( occupied Poznań ) , where hundreds of prisoners were killed by means of carbon monoxide poisoning , in an improvised gas chamber developed by Dr Albert Widmann , chief chemist of the German Criminal Police ( Kripo ) . In December 1939 , '' Reichsführer-SS '' Heinrich Himmler witnessed one of these gassings , ensuring that this invention would later be put to much wider uses
Operation Tannenberg
Operation Tannenberg
Aktion T4