SM U - 23 ( Austria - Hungary ) SM " U - 23 or U - XXIII " was a or U - boat built for and operated by the Austro - Hungarian Navy ( ) during the First World War . The design for " U - 23 " was based on submarines of the Royal Danish Navy ' s " Havmanden " class ( three of which had been built in Austria - Hungary ) , and was largely obsolete by the beginning of the war . " U - 23 " was just over long and was armed with two bow torpedo tubes , a deck gun , and a machine gun . In February 1918 , " U - 23 " was sunk with all hands by the Italian destroyer " Airone " while attempting an attack on the Italian transport . " U - 23 " had no wartime successes . Design and construction . When it became apparent to the Austro - Hungarian Navy 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 , 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 on 27 March 1915 . " U - 23 " was one of two boats of the class to be built at the Hungarian 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 surfaced and submerged and was designed for a complement of 18 . She was long with a beam of and a draft of . For propulsion , she featured a single shaft , a single diesel engine for surface running , and a single electric motor for submerged travel . She was capable of while surfaced and 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 at , surfaced , and at submerged . " U - 23 " was armed with two 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 and an machine gun . 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 - 23 " s 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 " Airone " which first tried to ram the U - boat , and then deployed an explosive paravane . 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 .