 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.As one of the eight original German Type IX submarines, later designated IXA, "U-43" had a displacement of when at the surface and while submerged.