25th U-boat Flotilla () was formed in Danzig in April 1940 as a training flotilla responsible for Firing Training. It moved bases several times throughout the war. Between June 1941 and September 1941 it moved to Drontheim. Then it was shifted to Memel and subsequently to Libau. At the end of 1944 it was shifted again to Gotenhafen and then finally in 1945 it moved to Travemünde. The Flotilla was originally called 2. Unterseebootsausbildungsflottille until July 1940 when it was renamed 25. Unterseebootsflottille.