Plan Z
"U-104" was ordered by the "Kriegsmarine" on 24 May 1938 (as part of Plan Z and in violation of the Treaty of Versailles). Her keel was laid down on 10 November 1939 by DeSchiMAG AG Weser in Bremen as yard number 967. "U-104" was launched on 25 May 1940 and commissioned on 19 August of that year under the command of "Kapitänleutnant" Harald Jürst.