After the invasion of Poland in September 1939, the secret Aktion T4 euthanasia programme – the systematic murder of German, Austrian and Polish hospital patients with mental or physical disabilities authorized by Hitler;– was initiated by the "SS" in order to eliminate "life unworthy of life" (), a Nazi designation for people who they considered to have no right to life. In 1941, the experience gained in the secretive killing of these hospital patients led to the creation of extermination camps for the implementation of the Final Solution. By then, the Jews were already confined to new ghettos and interned in Nazi concentration camps along with other targeted groups, including Roma, and the Soviet POWs. The Nazi "Endlösung der Judenfrage" (The Final Solution of the Jewish Question), based on the systematic killing of Europe's Jews by gassing, began during Operation Reinhard, after the June 1941 onset of the Nazi-Soviet war. The adoption of the gassing technology by Nazi Germany was preceded by a wave of hands-on killings carried out by the SS "Einsatzgruppen", who followed the Wehrmacht army during Operation Barbarossa on the Eastern Front.