As of 1934, the concentration camps and later also the extermination camps of the nazis were controlled by the SS, a paramilitary organisation of the NSDAP, Hitler's party. SS was an abbreviation for Schutzstaffel (protection squadron). The SS was established in 1925 as a personal protection squadron for Hitler, which, as of 1929 and under leadership of Heinrich Himmler, developed into one of the largest and most powerful organisations in nazi Germany. Himmler was the chief designer and the motor behind the Endlösung, the final solution to the Jewish question. A notorious unit of the SS was the Totenkopfverbände (Death's Head Unit) (known for the skull on the collar of their uniform), which was incorporated into the Waffen-SS (military force of the German Reich) as a military division during the war. The Einsatzgruppen were special units of the SS that carried out operations behind the frontlines. After the invasion of Poland (1939) and the war with the Soviet Union (1914), large-scale murders were carried out mainly by the Einsatzgruppen and groups of the Ordnungspolizei. Hundreds of thousands of Poles, Jews, and Russians were murdered during these mass executions.