During World War One, U-27 was launched on July 14, 1913, and commissioned into the Kaiserliche Marine on May 8, 1914 with Kapitänleutnant Wegener in command. In ten war patrols, Wegener sank 29 ships totaling 29,402 tons.
On August 19, 1915, U-27 was sunk and her entire crew including Kptlt. Wegener was killed in the Baralong Incident.
U-27 conducted one war patrol, sinking two ships totalling 624 tons.
U-27 suffered no casualties to any of her crews. On September 20, 1939, she was sunk west of Scotland by depth charges from the British destroyers HMS Fortune and Forester. All 38 crewmen survived.