The SS (Schutzstaffel; Protection Squadrons) was originally a paramilitary organization that provided security to the Nazi Party.
Under the leadership of Heinrich Himmler, the SS expanded to become a virtual state within the state in Nazi Germany: responsible for enforcing Nazi racial policies, identifying and persecuting political and other opponents of the Nazi regime.
Beginning in March 1933, the SS ran the network of concentration camps in which opponents of the Nazi regime were imprisoned, tortured, and often killed. From 1941, this included the death camps in Nazi-occupied Poland where millions of Jews were murdered during the Holocaust. To do this, the SS applied knowledge and techniques developed to kill the physically and mentally disabled in the T4 “Euthanasia” programme between 1939 and 1941.