20th U-boat Flotilla ("20. Unterseebootsflottille") was a training flotilla ("Ausbildungsflottille ") of the German Kriegsmarine during World War II. The flotilla was formed in Pillau, in June 1943 under the command of Korvettenkapitän Ernst Mengersen, and specialised in tactical training (Vortaktische Ausbildung). It was disbanded in February 1945.