SM UB-21

SM UB-21 was a German Type UB II submarine or U-boat in the German Imperial Navy (Kaiserliche Marine) 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 20 February 1916 as SM UB-21. The submarine sank 33 ships in 26 patrols for a total of. Surrendered to Britain in accordance with the requirements of the Armistice with Germany, UB-21 was sunk as a target by HMS Terror in the Solent on 30 September 1920; the wreck was sold in 1970 and most had been cleared by 1998, although some remnants survive.

Design
A Type UB II submarine, UB-21 had a displacement of 263 t when at the surface and 292 t while submerged. She had a total length of 36.13 m, a beam of 4.36 m, and a draught of 3.70 m. The submarine was powered by two Körting six-cylinder, four-stroke diesel engines producing a total of 280 PS, two Siemens-Schuckert electric motors producing 280 PS, and one propeller shaft. She was capable of operating at depths of up to 50 m.

The submarine had a maximum surface speed of 9.15 kn and a maximum submerged speed of 5.81 kn. When submerged, she could operate for 45 nmi at 4 kn; when surfaced, she could travel 6650 nmi at 5 kn. UB-21 was fitted with two 50 cm torpedo tubes, four torpedoes, and one 5 cm SK L/40 deck gun. She had a complement of twenty-one crew members and two officers and a 45-second dive time.