SM U-104 was a German Type U 57 U-boat during the First World War. U-104 was built at AG Weser in Bremen, launched on 3 July 1917 and commissioned on 12 August 1917. She completed four patrols under Kptlt. Kurt Bernis and was responsible for the sinking of nine vessels of a total of 14,721 gross register tons (GRT).