U-20-class submarine

SM U-21 loads a torpedo during World War I.
Class overview
Builders	Pola Navy Yard, Pola (2)[1] Hungarian UBAG yard, Fiume (2)[1]
Operators	Austro-Hungarian Navy
Preceded by	SM U-14
Succeeded by	U-27 class
Built	1915–1917
In commission	1916–1918
Completed	4
Lost	2
Preserved	0
General characteristics
Type	submarine
Displacement	173 tonnes (191 short tons) surfaced 210 tonnes (231 short tons) submerged[1]
Length	127 ft 2 in (38.76 m)[1]
Beam	13 ft (4.0 m)[1]
Draft	9 ft (2.7 m)[1]
Propulsion	1 × shaft 1 × diesel engine, 450 bhp (340 kW) 1 × electric motor, 160 shp (120 kW)[1]
Speed	12 knots (22 km/h) surfaced 9 knots (17 km/h) submerged[1]
Range	1,400 nautical miles (2,600 km) at 10 knots (19 km/h) surfaced[2] 23 nautical miles (43 km) at 8 knots (15 km/h) submerged
Complement	18[1]
Armament	2 × 45 cm (17.7 in) torpedo tubes (both in front); 2 torpedoes 1 × 66 mm/26 (2.6 in) deck gun 1 × 8 mm (0.31 in) machine gun[1]

The U-20 class was a class of four submarines or U-boats built for and operated by the Austro-Hungarian Navy (German: Kaiserliche und Königliche Kriegsmarine or K.u.K. Kriegsmarine) during World War I. The class is sometimes referred to as the Havmanden class because it was based upon the design of the Royal Danish Navy's 1911 Havmanden-class submarines, three of which were built in Fiume.

With a small fleet of six U-boats at the beginning of World War I, two of which were not operational, the Austro-Hungarian Navy acted to bolster its fleet. They reluctantly ordered four U-20 boats in 1915 because construction could start immediately, even though the Havmanden-class design was largely obsolete by the beginning of the war. Political considerations caused the order to be split between Austrian and Hungarian firms, which contributed to construction problems and delays, keeping any of the boats from being operational until the middle of 1917.

The class boats were just over 127 feet (39 m) long and were armed with two front torpedo tubes, a deck gun, and a machine gun. The engines for the boats were unreliable, which compounded handling problems with the design. The U-20 class did not claim any wartime successes, yet lost two of the boats—U-20 and U-23—to enemy action during the war. The remaining two were delivered as war reparations and broken up. The conning tower from U-20, which was raised and salvaged in 1962, is on display in a military museum in Vienna.