SM U-23 or U-XXIII was a or U-boat

U-boat

U-boat is the anglicized version of the German word U-Boot , itself an abbreviation of Unterseeboot , and refers to military submarines operated by Germany, particularly in World War I and World War II...

 built for and operated by the Austro-Hungarian Navy

Austro-Hungarian Navy

The Austro-Hungarian Navy was the naval force of Austria-Hungary. Its official name in German was Kaiserliche und Königliche Kriegsmarine , abbreviated as k.u.k. Kriegsmarine....

  during the First World War. The design for U-23 was based on submarines of the Royal Danish Navy

Royal Danish Navy

The Royal Danish Navy is the sea-based branch of the Danish Defence force. The RDN is mainly responsible for maritime defence and maintaining the sovereignty of Danish, Greenlandic and Faroese territorial waters...

's Havmanden class

Havmanden class submarine (1911)

The Havmanden class was a class of six submarines built for the Royal Danish Navy from 1911 to 1914. Also later known as the A class, the boats were designed by the Austro-Hungarian firm Whitehead & Co. of Fiume...

 (three of which had been built in Austria-Hungary

Austria-Hungary

Austria-Hungary , more formally known as the Kingdoms and Lands Represented in the Imperial Council and the Lands of the Holy Hungarian Crown of Saint Stephen, was a constitutional monarchic union between the crowns of the Austrian Empire and the Kingdom of Hungary in...

), and was largely obsolete by the beginning of the war.

U-23 was just over 127 feet (38.7 m) long and was armed with two bow torpedo tubes, a deck gun

Deck gun

A deck gun is a type of artillery cannon mounted on the deck of a ship or submarine.The deck gun was used as a defensive weapon against smaller boats or ships and in certain cases where torpedo use was limited. Typically a crew of three; gunner, loader, and layer, operated the gun, while others...

, and a machine gun

Machine gun

A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....

. In February 1918, U-23 was sunk with all hands by the Italian destroyer

Destroyer

In naval terminology, a destroyer is a fast and maneuverable yet long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against smaller, powerful, short-range attackers. Destroyers, originally called torpedo-boat destroyers in 1892, evolved from...

 Airone while attempting an attack on the Italian transport

Transport

Transport or transportation is the movement of people, cattle, animals and goods from one location to another. Modes of transport include air, rail, road, water, cable, pipeline, and space. The field can be divided into infrastructure, vehicles, and operations...

 . U-23 had no wartime successes.

Design and construction

When it became apparent to the Austro-Hungarian Navy

Austro-Hungarian Navy

The Austro-Hungarian Navy was the naval force of Austria-Hungary. Its official name in German was Kaiserliche und Königliche Kriegsmarine , abbreviated as k.u.k. Kriegsmarine....

 that the First World War would not be a short one, they moved to bolster their U-boat fleet by seizing the plans for the Danish Havmanden class submarines

Havmanden class submarine (1911)

The Havmanden class was a class of six submarines built for the Royal Danish Navy from 1911 to 1914. Also later known as the A class, the boats were designed by the Austro-Hungarian firm Whitehead & Co. of Fiume...

, three of which had been built at Whitehead & Co. in Fiume. Although the Austro-Hungarian Navy was not happy with the design, which was largely obsolete, it was the only design for which plans were available and which could be begun immediately in domestic shipyards. The Austro-Hungarian Navy unenthusiastically placed orders for U-23 and her three sister boats

Sister ship

A sister ship is a ship of the same class as, or of virtually identical design to, another ship. Such vessels share a near-identical hull and superstructure layout, similar displacement, and roughly comparable features and equipment...

 on 27 March 1915.

U-23 was one of two boats of the class to be built at the Hungarian UBAG yard in Fiume. Due to demands by the Hungarian government, subcontracts for the class were divided between Hungarian and Austrian firms, and this politically expedient solution worsened technical problems with the design, resulting in numerous modifications and delays for the class in general.

U-23 was an ocean-going submarine that displaced 173 tonnes (190.7 ST) surfaced and 210 tonnes (231 ST) submerged and was designed for a complement of 18. She was 127 in 2 in (38.76 m) long with a beam

Beam (nautical)

The beam of a ship is its width at the widest point. Generally speaking, the wider the beam of a ship , the more initial stability it has, at expense of reserve stability in the event of a capsize, where more energy is required to right the vessel from its inverted position...

 of 13 feet (4 m) and a draft

Draft (hull)

The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull , with the thickness of the hull included; in the case of not being included the draft outline would be obtained...

 of 9 feet (2.7 m). For propulsion, she featured a single shaft, a single 450 bhp diesel engine

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

 for surface running, and a single 160 shp electric motor for submerged travel. She was capable of 12 knots while surfaced and 9 knots while submerged. Although there is no specific notation of a range for U-23, the Havmanden class, upon which the U-20 class was based, had a range of 1400 nautical miles (2,592.8 km) at 10 knots, surfaced, and 23 nautical miles (42.6 km) at 8 knots submerged.

U-23 was armed with two 45 cm (17.7 in) torpedo tubes located in the front and carried a complement of two torpedoes. She was also equipped with a 66 mm/26 (2.6 in) deck gun

Deck gun

A deck gun is a type of artillery cannon mounted on the deck of a ship or submarine.The deck gun was used as a defensive weapon against smaller boats or ships and in certain cases where torpedo use was limited. Typically a crew of three; gunner, loader, and layer, operated the gun, while others...

 and an 8 mm (0.31496062992126 in) machine gun

Machine gun

A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....

.

Service career

U-23 was launched on 5 January 1917, but It is not known with certainty when U-23 was commissioned. Author Paul Halpern reports that U-23 and her three sisters all entered service between August and November 1917. Although there are no specific reports of problems with U-23, the U-20 class as a whole suffered from unreliable engines which compounded the poor handling characteristics of the boats.

On 21 February 1918, Linienschiffsleutnant Klemens Ritter von Bézard, U-23s only commanding officer, was guiding the boat in an attack on the Italian transport in the Straits of Otranto. U-23 came under attack the Italian destroyer

Destroyer

In naval terminology, a destroyer is a fast and maneuverable yet long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against smaller, powerful, short-range attackers. Destroyers, originally called torpedo-boat destroyers in 1892, evolved from...

 Airone which first tried to ram the U-boat, and then deployed an explosive paravane

Paravane (weapon)

The paravane is a form of towed underwater "glider". It was developed by Cdr Usborne and Lt Burney financed by Sir George White, founder of the Bristol Aeroplane Company....

. When the paravane contacted the submerged U-23, it blew debris into the air, sinking the submarine with all hands. Like all of her sister boats, U-23 had no wartime successes.