German submarine U-138 was a Type IID U-boat of the German Kriegsmarine in World War II. Her keel was laid down on 16 November 1939 by Deutsche Werke in Kiel as 'werk' 267. She was launched on 18 May 1940 and commissioned on 27 June 1940 with Oberleutnant zur See Wolfgang Lüth in command. U-138 conducted five patrols, sinking six ships totalling and damaged one vessel of 6,993 GRT. She was sunk in June 1941 by British warships west of Cadiz in Spain. There were no casualties from her crew of 27.