Operation Tannenberg was codename for one of extermination actions directed at Polish intelligentsia during World War II. Nazis prepared lists, so called Sonderfahndungsbuch Polen, which listed more than 60,000 Polish activists, intelligentsia, actors, former officers, etc. First, in August 1939 about 2,000 activists of Polish ethnicity in Germany were arrested and murdered. The second part of the action started September 1, 1939 and ended in October resulting in at least 20,000 murdered in 760 mass executions by special units, so-called Einsatzgruppen, in addition to regular Wehrmacht units and SS.