SM U-20 (Austria-Hungary)

When it became apparent to the Austro-Hungarian Navy that the First World War would not be a short war,[1] they moved to bolster their U-boat fleet by seizing the plans for Denmark's Havmanden class submarines,[7] which had been designed by Whitehead & Co. in Fiume, who had built three units.[6] Although the Austro-Hungarian Navy was not happy with the design, which was largely obsolete,[8][9] it was the only design for which plans were available and which could be begun immediately in domestic shipyards.[9] The Austro-Hungarian Navy unenthusiastically placed orders for U-20 and her three sister boats on 27 March 1915.[1]

U-20 was one of two boats of the class to be built at the Pola Navy Yard.[7] Due to demands by the Hungarian government,[1] subcontracts for the class were divided between Hungarian and Austrian firms,[2] but this politically expedient solution worsened technical problems with the design and resulted in numerous modifications and delays for the class in general.[7]

U-20 was a coastal submarine that displaced 173 tonnes (191 short tons) surfaced and 210 tonnes (231 short tons) submerged and was designed for a complement of 18. She was 127 feet 2 inches (38.76 m) long with a beam of 13 feet (4.0 m) and a draft of 9 feet (2.7 m). For propulsion, she featured a single propeller shaft, a single 450 bhp (340 kW) diesel engine for surface running, and a single 160 shp (120 kW) electric motor for submerged travel.[2] She was capable of 12 knots (22 km/h) while surfaced and 9 knots (17 km/h) while submerged. Although there is no specific notation of a range for U-20, the Havmanden class, upon which the U-20 class was based, had a range of 1,400 nautical miles (2,600 km) at 10 knots (19 km/h), surfaced, and 23 nautical miles (43 km) at 8 knots (15 km/h) submerged.[6]

U-20 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 (2.6 in) deck gun and an 8 mm (0.31 in) machine gun.[2]

U-20 was laid down on 29 September 1915,[3] six months after she was ordered,[1] and was launched on 18 September 1916.[2]

The conning tower of U-20 on display at the Heeresgeschichtliches Museum in Vienna

Details of U-20 conning tower.

Upon completion, U-20 began diving trials. On her 15 March 1917 trial, she was accidentally rammed by Admiral Spaun in the Fasana Channel. The collision with the Austro-Hungarian light cruiser twisted U-20's periscope, extensively damaged the conning tower, and knocked off her deck gun. After seven months of reconstruction, U-20 was commissioned into the Austro-Hungarian Navy on 20 October.[3]

After initially operating out of Pola, U-20 was transferred to Trieste in February 1918. Over the next three months, the U-boat patrolled in the northern Adriatic between the Tagliamento estuary and Venice. U-20 had an encounter with an enemy submarine on 7 April but was not able to successfully launch an attack.[3] On 3 July, Linienschiffsleutnant Ludwig Müller sailed U-20 out from Trieste for the Gulf of Venice. A day later, U-20 was spotted by the Italian submarine F-12, which was on patrol in the northern Adriatic. F-12 initially pursued U-20 underwater, and then on the surface. At a range of 650 yards (590 m), F-12 torpedoed U-20 at position 45°29′N 13°05′E, sinking her with all hands. There was no wreckage on the surface, only an oil slick.[4][Note 1] Like all of her sister boats,[7] U-20 had no wartime successes.[5]

In mid 1962, the wreck of U-20 was discovered in the northern Adriatic. Italian salvage crews raised the boat's rear portion on 22 July and her front section on 21 November.[4] The conning tower and a small midships section of U-20 were donated to the Heeresgeschichtliches Museum in Vienna, where they are on display, while the rest of the boat was scrapped.[7] The remains of the crewmen were buried on the grounds of the Theresian Military Academy at Wiener Neustadt.[10]