Sicherheitsdienst (German: [ˈzɪçɐhaɪtsˌdiːnst] , "Security Service"), full title Sicherheitsdienst des Reichsführers-SS ("Security Service of the Reichsführer-SS"), or SD, was the intelligence agency of the SS and the Nazi Party in Nazi Germany. Established in 1931, the SD was the first Nazi intelligence organization and the Gestapo (formed in 1933) was considered its sister organization through the integration of SS members and operational procedures. The SD was administered as an independent SS office between 1933 and 1939. That year, the SD was transferred over to the Reich Security Main Office (Reichssicherheitshauptamt; RSHA), as one of its seven departments. Its first director, Reinhard Heydrich, intended for the SD to bring every single individual within the Third Reich's reach under "continuous supervision".
Following Germany's defeat in World War II, the tribunal at the Nuremberg trials officially declared that the SD was a criminal organisation, along with the rest of Heydrich's RSHA (including the Gestapo) both individually and as branches of the SS in the collective. Heydrich was assassinated in 1942; his successor, Ernst Kaltenbrunner, was convicted of war crimes and crimes against humanity at the Nuremberg trials, sentenced to death and hanged in 1946.
