In September 1941, through the "Action Lauterbacher" plan, a ghettoisation of the remaining Hanoverian Jewish families began. Even before the Wannsee Conference, on 15 December 1941, the first Jews from Hanover were deported to Riga. A total of 2,400 people were deported, and very few survived. During the war seven concentration camps were constructed in Hanover, in which many Jews were confined. Of the approximately 4,800 Jews who had lived in Hannover in 1938, fewer than 100 were still in the city when troops of the United States Army arrived on 10 April 1945 to occupy Hanover at the end of the war.[citation needed] Today, a memorial at the Opera Square is a reminder of the persecution of the Jews in Hanover. After the war a large group of Orthodox Jewish survivors of the nearby Bergen-Belsen concentration camp settled in Hanover.

What plan was implemented in September 1941?