Sichereitsdienst
The Sicherheitsdienst, usually referred to as the SD, was the intelligence service of the SS and one of the most important instruments of Nazi control and terror before and during the Second World War. It was created in 1931 under the direction of Reinhard Heydrich, who at that time was a young but highly ambitious SS officer. Heinrich Himmler, leader of the SS, gave Heydrich the task of building a party intelligence service that would identify enemies of National Socialism both inside and outside Germany. From the start, the SD was designed to be more than a police body; it was intended to be an ideological surveillance organization that could monitor public opinion, loyalty, and political reliability across the entire society.
The SD began as a small unit working out of Munich, but after the Nazis came to power in 1933 it expanded rapidly. By the mid-1930s it had its headquarters in Berlin, in the Prinz-Albrecht-Straße complex, which later became notorious as the center of Nazi security organizations. From there, the SD operated through a nationwide and eventually Europe-wide network of offices. Inside Germany, SD sections were attached to SS regional commands, known as Oberabschnitte and Abschnitte, ensuring that intelligence flowed directly from towns, workplaces, universities, churches, and social organizations back to Berlin.
One of the SD’s most important functions was gathering information about the German population. Unlike the Gestapo, which focused on investigating and arresting people suspected of specific crimes, the SD aimed to build a broad picture of what people thought and felt. Its agents and informers wrote thousands of reports on morale, political opinions, religious life, rumors, jokes, and even private conversations. These reports were summarized in regular “mood” and “situation” reports that went to top Nazi leaders. This gave the regime a powerful tool to sense potential unrest, resistance, or dissatisfaction long before it turned into open opposition.
In 1939, shortly before the outbreak of war, the SD was formally merged into a much larger structure called the Reich Main Security Office, or RSHA. This brought together the SD, the Gestapo, and the criminal police under one command, again led by Heydrich. Within the RSHA, the SD was divided into two main branches: one for internal intelligence within the Reich, and one for foreign intelligence. The internal SD monitored Germans and occupied populations, while the foreign SD ran espionage, political intelligence, and analysis on other countries.
By the early years of the war, the SD had grown into a massive organization. Tens of thousands of full-time staff and an even larger number of informers and collaborators worked for it across Germany and occupied Europe. While exact numbers are difficult to pin down, historians estimate that the RSHA as a whole employed around 50,000 people, with the SD forming a large and influential part of that total. In addition, it relied on countless voluntary or coerced informants who reported on neighbors, coworkers, and even family members.
The SD held enormous power because it was both an intelligence service and part of a system that could directly lead to arrest, imprisonment, or death. Its reports were used to justify crackdowns on political opponents, Jews, Roma, clergy, intellectuals, and anyone considered “asocial” or dangerous to Nazi rule. In occupied territories such as Poland, France, the Netherlands, and the Soviet Union, SD officers worked closely with the Gestapo and the Einsatzgruppen, the mobile killing units that carried out mass shootings of Jews, communists, and other targeted groups. The SD often identified who should be arrested or killed by compiling lists of local elites, resistance members, and community leaders.
The SD also played a key role in the Holocaust. Its foreign and domestic branches collected detailed information on Jewish communities, political organizations, and social networks, which helped the Nazis plan deportations and extermination. In the East, SD officers were present at or helped organize mass murder operations, especially in 1941 and 1942. Their intelligence work made the killing more systematic and efficient, because it told the regime exactly who lived where and who was likely to resist.
Reinhard Heydrich remained the most important figure in the SD until his assassination in Prague in 1942. After his death, Ernst Kaltenbrunner took over the RSHA, and the SD continued its work until the collapse of Nazi Germany in 1945. By the end of the war, the SD had offices and agents across most of Europe, from Norway to Greece, and from France deep into the occupied Soviet territories.
After the war, the SD was declared a criminal organization by the Allied war crimes tribunals because of its central role in repression, terror, and genocide. Many of its leaders were tried and executed or imprisoned, although a significant number of lower-level members escaped justice and later reintegrated into postwar society. The history of the SD stands as a clear example of how intelligence services, when fused with extremist ideology and unlimited power, can become instruments of mass violence and total control.
