German submarine U-139 was a Type IID U-boat of the German Navy during World War II. Her keel was laid down on 20 November 1939 by Deutsche Werke in Kiel as 'werk' 268. She was launched on 28 July 1940 and commissioned on 24 July 1940 with Kapitänleutnant Robert Bartels in command. U-137 began her service life with the 1st U-boat Flotilla. She was then assigned to the 21st flotilla and subsequently to the 22nd flotilla where she conducted two patrols, but did not sink or damage any ships. She spent the rest of the war as a training vessel. She was scuttled in May 1945.