As a result of the German invasion of Poland, which started World War II in September 1939, Pułtusk was occupied by the Wehrmacht and incorporated into Nazi Germany. Already on September 12-13, 1939, the "Einsatzgruppe V" entered the town to commit atrocities against the population. Nazi Germany operated a police prison, court prison and forced labour camp in the town. The German police carried out executions of Poles in the local prison in November and December 1939. During the German occupation, approximately 50% of the city's inhabitants, mostly Jews, were expelled or deported, some to Nazi concentration camps. In 1941-1945 it was renamed in German as "Ostenburg", to erase traces of Polish origin. On December 17, 1942, the Gestapo carried out a public execution of four members of the Home Army, the leading Polish resistance organization. In the battle for Pułtusk during later World War II, over 16,000 soldiers of the Soviet Red Army were killed. As a result of the battle, approximately 85% of the city was destroyed.