At 04:45 on 4 October 1939,
U-23 scored one of the
Kriegsmarines early successes of the war when she torpedoed and sank with gunfire, the merchant ship
Glen Farg about south-southwest of
Sumburgh Head (southern Shetland). One person died, while 16 survivors were picked up by and landed at
Kirkwall the next day. In 16 patrols
U-23 sank seven ships for a total of including two
warships, as well as damaging a warship and an
auxiliary warship. Over the course of her service with the
Kriegsmarine,
U-23 had ten commanding officers, the most famous of whom was
Kapitänleutnant Otto Kretschmer, who went on to become the top scoring U-boat ace. After service in the Atlantic with the
1st U-boat Flotilla,
U-23 served as a training boat with the
21st U-boat Flotilla from July 1940 until September 1942.
U-23 was then transported in sections along the Danube to the Romanian port of
Galați. She was then re-assembled by the Romanians at the
Galați shipyard and sent to the
Black Sea port of
Constanţa, Romania, with the
30th U-boat Flotilla until September 1944. ==Fate==