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The Sicherheitsdienst (SD), or Security Service, was an intelligence agency within the Nazi Party of Germany. It was organized in 1931 by Reinhard Heydrich and was tasked with gathering intelligence, suppressing internal dissent, and carrying out covert operations. The SD played a key role in the Nazi regime, providing information that was used to target political opponents, Jews, and other groups deemed undesirable by the Nazis.