Plan Z
"U-43" was ordered for the "Kriegsmarine" on 21 November 1936 (as part of Plan Z and in violation of the Treaty of Versailles). Her keel was laid down on 15 August 1938 by AG Weser, Bremen as yard number 946. She was launched on 23 May 1939 and commissioned on 26 August of that same year under the command of "Korvettenkapitän" Wilhelm Ambrosius.