The Sicherheitsdienst (Security Service), commonly known as the SD, was an intelligence agency of the Nazi regime. Established in 1931, it remained operational until the fall of Nazi Germany in 1945.
Throughout most of its existence, it was under the leadership of Reinhard Heydrich. The SD was an extremist organization with radical ideological beliefs and played a major role in perpetrating the Holocaust.
Functioning as a subgroup of the SS (Schutzstaffel, Protection Squadron), which was the elite paramilitary organization of the Nazi Party headed by Heinrich Himmler, the SD was primarily responsible for gathering intelligence about those who were perceived as enemies of the Nazi Party.
This included individuals such as political opponents, Jews, and Freemasons, among others.
The SD became one of the primary sources of information about Jews for the Nazi regime, and as such, it proposed and experimented with various methods for solving the "Jewish Question".
