Prior to AB-Aktion, in late 1939 and early 1940, most Polish university professors, intellectuals, writers, politicians, teachers and other members of the elite of Polish society were briefly arrested by the Gestapo and had their names registered. Frank finally accepted and approved the Ausserordentliche Befriedungsaktion on May 16, 1940. In the following weeks, the German police, Gestapo, SD (Sicherheitsdienst) and units of the Wehrmacht arrested roughly 30,000 Poles in major Polish cities, including Warsaw, Łódź, Lublin and Kraków.