German submarine U-39 was a Type IXA U-boat of the Kriegsmarine that operated from 1938 to the first few days of World War II. She was ordered by the Kriegsmarine on 29 July 1936 as part of the re-armament program (Aufrüstung) in Germany, which was illegal under the terms of the Treaty of Versailles. The keel for U-39 was laid down on 2 June 1937, by AG Weser of Bremen. She was commissioned on 10 December 1938 with Kapitänleutnant Gerhard Glattes in command. U-39 was the first German U-boat to be sunk in World War II.