German U-boat bases in occupied Norway operated between 1940 and 1945, when the Kriegsmarine (German navy), converted several naval bases in Norway into submarine bases. Norwegian coastal cities became available to the Kriegsmarine after the invasion of Denmark and Norway in April 1940. Following the conclusion of the Norwegian Campaign (June 1940), the occupying Germans began to transfer U-boats stationed in Germany to many Norwegian port cities such as Bergen, Narvik, Trondheim, Hammerfest and Kirkenes.