Her construction was ordered on 12 June 1912 and her keel was laid down on 3 April 1913 by Germaniawerft of Kiel. She was launched on 22 October 1914 and commissioned on 14 February 1915 under the command of Gerhardt Fürbringer. Second officer was lieutenant Rudolf Jauch (of the Jauch family). U-40 conducted one patrol, without sinking a ship.