SM UB-20 was a German Type UB II submarine or U-boat in the German Imperial Navy () during World War I. The U-boat was ordered on 30 April 1915 and launched on 26 September 1915. She was commissioned into the German Imperial Navy on 10 February 1916 as SM UB-20. The submarine sank 13 ships in 15 patrols for a total of . UB-20 was mined and sunk on 28 July 1917 at . Fifteen crew members died in the event.
Design A Type UB II submarine, UB-20 had a displacement of when at the surface and while submerged. She had a total length of , a beam of , and a draught of . The submarine was powered by two Körting six-cylinder, four-stroke diesel engines each producing a total , a Siemens-Schuckert electric motor producing , and one propeller shaft. She was capable of operating at depths of up to .
The submarine had a maximum surface speed of and a maximum submerged speed of . When submerged, she could operate for at ; when surfaced, she could travel at . UB-20 was fitted with two torpedo tubes, four torpedoes, and one SK L/40 deck gun. She had a complement of twenty-three crew members and two officers and a 45-second dive time.
Loss At noon on 28.07.1917 UB 20 left Ostend for a four-hour sea trial in the area around West Hinder lightship. The boat did not return. (Pos. 51°21'N-02°38'E). The commander's body was washed up on the Jutland coast near Lodbjerg on 03.08.1917 and buried in the local cemetery.
Summary of raiding history DateNameNationalityTonnageTonnages are in gross register tonsFate2 August 1916Bror Oskar368Sunk2 August 1916Commerce638Sunk2 August 1916Themis1,047Captured as prize2 August 1916Vera312Sunk2 August 1916Vermland213Sunk10 April 1917Pluto1,266Sunk7 May 1917Martha Maria176Sunk7 May 1917Prins Hendrik De Nederlande182Sunk16 May 1917Friso171Sunk17 May 1917Kilmaho2,155Sunk18 May 1917Adventure50Sunk18 May 1917Primrose62Sunk19 May 1917Askild2,540Sunk20 May 1917Normand2,097Sunk11 June 1917Knight Companion7,241Damaged
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