(, ; also 'task forces') were (SS) paramilitary death squads of Nazi Germany that were responsible for mass murder, primarily by shooting, during World War II (1939–1945) in German-occupied Europe. The had an integral role in the implementation of the so-called "Final Solution to the Jewish question" () in territories conquered by Nazi Germany, and were involved in the murder of much of the intelligentsia and cultural elite of Poland, including members of the Catholic priesthood. Almost all of the people they murdered were civilians, beginning with the intelligentsia and swiftly progressing to Soviet political commissars, Jews, and Romani people, as well as actual or alleged partisans throughout Eastern Europe.
Under the direction of Heinrich Himmler and the supervision of SS- Reinhard Heydrich, the operated in territories occupied by the Wehrmacht (German armed forces) following the invasion of Poland in September 1939 and the invasion of the Soviet Union in June 1941. The worked hand-in-hand with the Order Police battalions on the Eastern Front to carry out operations ranging from the murder of a few people to operations which lasted over two or more days, such as the massacre at Babi Yar with 33,771 Jews murdered in two days, and the Rumbula massacre (with about 25,000 Jews murdered in two days of shooting). As ordered by Nazi leader Adolf Hitler, the Wehrmacht cooperated with the , providing logistical support for their operations, and participated in the mass murders. Historian Raul Hilberg estimates that between 1941 and 1945 the , related agencies, and foreign auxiliary personnel murdered more than two million people, including 1.3 million of the 5.5 to 6 million Jews murdered during the Holocaust.
After the close of World War II, 24 officers, including multiple commanding officers, of the were prosecuted in the Einsatzgruppen trial in 1947–48, charged with crimes against humanity and war crimes. Fourteen death sentences and two life sentences were handed out. However, only four of these death sentences were carried out. Four additional leaders were later tried and executed by other nations.
Formation and Aktion T4
The were formed under the direction of SS- Reinhard Heydrich and operated by the (SS) before and during World War II. The had their origins in the ad hoc formed by Heydrich to secure government buildings and documents following the in Austria in March 1938. Originally part of the (Security Police; SiPo), two units of were stationed in the Sudetenland in October 1938. When military action turned out not to be necessary due to the Munich Agreement, the were assigned to confiscate government papers and police documents. They also secured government buildings, questioned senior civil servants, and arrested as many as 10,000 Czech communists and German citizens. From September 1939, the (Reich Security Main Office; RSHA) had overall command of the .
As part of the drive by the Nazi regime to remove so-called "undesirable" elements from the German population, from September to December 1939 the and others took part in Action T4, a program of systematic murder of persons with physical and mental disabilities and patients of psychiatric hospitals. Aktion T4 mainly took place from 1939 to 1941, but the murders continued until the end of the war. Initially the victims were shot by the and others, but gas chambers were put into use by spring 1940.
Invasion of Poland
In response to Adolf Hitler's plan to invade Poland on 1 September 1939, Heydrich re-formed the to travel in the wake of the German armies. Membership at this point was drawn from the SS, the (Security Service; SD), the police, and the Gestapo. Heydrich placed SS- Werner Best in command, who assigned to choose personnel for the task forces and their subgroups, called , from among educated people with military experience and a strong ideological commitment to Nazism. Some had previously been members of paramilitary groups such as the . Heydrich instructed Wagner in meetings in late July that the should undertake their operations in cooperation with the (Order Police; Orpo) and military commanders in the area. Army intelligence was in constant contact with to coordinate their activities with other units.