German submarine U-23 (1936)

German submarine U-23 was a Type IIB U-boat of Nazi Germany's Kriegsmarine, built in Germaniawerft, Kiel. She was laid down on 11 April 1936 and commissioned on 24 September.

Design
German Type IIB submarines were enlarged versions of the original Type IIs. U-23 had a displacement of 279 t when at the surface and 328 t while submerged. Officially, the standard tonnage was 250 LT, however. The U-boat had a total length of 42.70 m, a pressure hull length of 28.20 m, a beam of 4.08 m, a height of 8.60 m, and a draught of 3.90 m. The submarine was powered by two MWM RS 127 S four-stroke, six-cylinder diesel engines of 700 PS for cruising, two Siemens-Schuckert PG VV 322/36 double-acting electric motors producing a total of 460 PS for use while submerged. She had two shafts and two 0.85 m propellers. The boat was capable of operating at depths of up to 80 - 150 m.

The submarine had a maximum surface speed of 12 kn and a maximum submerged speed of 7 kn. When submerged, the boat could operate for 35 - 42 nmi at 4 kn; when surfaced, she could travel 3800 nmi at 8 kn. U-23 was fitted with three 53.3 cm torpedo tubes at the bow, five torpedoes or up to twelve Type A torpedo mines, and a 2 cm anti-aircraft gun. The boat had a complement of twentyfive.

Service history
At 04:45 on 4 October 1939, U-23 scored one of the Kriegsmarine's early successes of the war when she torpedoed and sank with gunfire, the merchant ship Glen Farg about 60 nmi south-southwest of Sumburgh Head (southern Shetland). One person died, while 16 survivors were picked up by HMS Firedrake (H79) 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
U-23 was scuttled by her crew on 10 September 1944, off the coast of Turkey in the Black Sea at position 41.18333°N, 30°W to prevent her capture by the advancing Soviets.

On 3 February 2008, The Daily Telegraph newspaper reported that U-23 had been discovered by Selçuk Kolay, a Turkish marine engineer, in 160 ft of water, three miles from the town of Ağva.