SM UB-21 was a German Type UB II submarine or U-boat in the German Imperial Navy (German: 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 36,764 gross register tons (GRT). Surrendered to Britain in accordance with the requirements of the Armistice with Germany, UB-21 sank in 1920 in the eastern Solent while en route to be broken up .
SM UB-45, a u-boat similar to UB-21
|Ordered:||30 April 1915|
|Builder:||Blohm & Voss, Hamburg|
|Launched:||26 September 1915|
|Completed:||18 February 1916|
|Commissioned:||20 February 1916|
|Class and type:||German Type UB II submarine|
|Draught:||3.70 m (12 ft 2 in)|
|Test depth:||50 m (160 ft)|
|Complement:||2 officers, 21 men|
|Notes:||45-second diving time|
A German Type UB II submarine, UB-21 had a displacement of 263 tonnes (259 long tons) when at the surface and 292 tonnes (287 long tons) while submerged. She had a total length of 36.13 m (118 ft 6 in), a beam of 4.36 m (14 ft 4 in), and a draught of 3.70 m (12 ft 2 in). The submarine was powered by two Körting six-cylinder, four-stroke diesel engines producing a total of 280 metric horsepower (280 shp; 210 kW), two Siemens-Schuckert electric motors producing 280 metric horsepower (210 kW; 280 shp), and one propeller shaft. She was capable of operating at depths of up to 50 metres (160 ft).
The submarine had a maximum surface speed of 9.15 knots (16.95 km/h; 10.53 mph) and a maximum submerged speed of 5.81 knots (10.76 km/h; 6.69 mph). When submerged, she could operate for 45 nautical miles (83 km; 52 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 6,650 nautical miles (12,320 km; 7,650 mi) at 5 knots (9.3 km/h; 5.8 mph). UB-21 was fitted with two 50 centimetres (20 in) torpedo tubes, four torpedoes, and one 5 cm (2.0 in) SK L/40 deck gun. She had a complement of twenty-one crew members and two officers and a 45-second dive time.
Summary of raiding history
|5 May 1916||Harald||275||Sunk|
|20 October 1916||Lekna||204||Sunk|
|20 October 1916||Randi||467||Sunk|
|20 October 1916||Svartvik||322||Sunk|
|21 October 1916||Fritzöe||641||Captured as a prize|
|21 October 1916||Grönhaug||667||Sunk|
|22 October 1916||London||184||Sunk|
|22 October 1916||Thor||372||Sunk|
|3 November 1916||Pluto||1,148||Captured as a prize|
|16 February 1917||Lady Ann||1,016||Sunk|
|17 February 1917||Excel||157||Sunk|
|22 February 1917||John Miles||687||Sunk|
|29 March 1917||Bywell||1,522||Sunk|
|31 March 1917||Norden||776||Captured as a prize|
|29 April 1917||Victoria||1,620||Sunk|
|2 May 1917||Rikard Noordrak||1,123||Sunk|
|5 May 1917||Edith Cavell||20||Sunk|
|6 May 1917||Harold||1,679||Sunk|
|8 May 1917||Batavier II||157||Captured as a prize|
|6 June 1917||S.N.A. 2||2,294||Sunk|
|7 June 1917||Sir Francis||1,991||Sunk|
|20 July 1917||Trelyon||3,099||Sunk|
|22 July 1917||Glow||1,141||Sunk|
|23 July 1917||Vanland||1,285||Sunk|
|24 August 1917||Springhill||1,507||Sunk|
|18 October 1917||Amsteldam||1,233||Sunk|
|19 October 1917||Gemma||1,385||Sunk|
|23 November 1917||Ocean||1,442||Sunk|
|29 December 1917||Inverness||3,734||Damaged|
|29 December 1917||Patria||838||Sunk|
|30 December 1917||Hercules||1,295||Sunk|
|25 March 1918||Hercules||1,095||Sunk|
|8 May 1918||Constantia||772||Sunk|
|10 May 1918||Anboto Mendi||2,114||Sunk|
|11 May 1918||Gothia||1,826||Sunk|
|12 May 1918||Haslingden||1,934||Sunk|
|4 July 1918||Mentor||539||Sunk|
|26 September 1918||Paul||659||Sunk|
- "SM" stands for "Seiner Majestät" (English: His Majesty's) and combined with the U for Unterseeboot would be translated as His Majesty's Submarine.
- Tonnages are in gross register tons
- Rössler 1979, p. 64.
- Gröner 1991, pp. 23-25.
- Helgason, Guðmundur. "WWI U-boat commanders: Ernst Hashagen (Royal House Order of Hohenzollern)". German and Austrian U-boats of World War I - Kaiserliche Marine - Uboat.net. Retrieved 29 January 2015.
- Helgason, Guðmundur. "WWI U-boat commanders: Franz Walther". German and Austrian U-boats of World War I - Kaiserliche Marine - Uboat.net. Retrieved 29 January 2015.
- Helgason, Guðmundur. "WWI U-boat commanders: Walter Scheffler". German and Austrian U-boats of World War I - Kaiserliche Marine - Uboat.net. Retrieved 29 January 2015.
- Helgason, Guðmundur. "WWI U-boat commanders: Bruno Mahn". German and Austrian U-boats of World War I - Kaiserliche Marine - Uboat.net. Retrieved 29 January 2015.
- Bendert 2000, p. 195.
- Helgason, Guðmundur. "Ships hit by UB-21". German and Austrian U-boats of World War I - Kaiserliche Marine - Uboat.net. Retrieved 29 January 2015.
- Bendert, Harald (2000). Die UB-Boote der Kaiserlichen Marine, 1914-1918. Einsätze, Erfolge, Schicksal (in German). Hamburg: Verlag E.S. Mittler & Sohn GmbH. ISBN 3-8132-0713-7.
- Gröner, Erich; Jung, Dieter; Maass, Martin (1991). U-boats and Mine Warfare Vessels. German Warships 1815–1945. 2. Translated by Thomas, Keith; Magowan, Rachel. London: Conway Maritime Press. ISBN 0-85177-593-4.
- Rössler, Eberhard (1979). U-Bootbau bis Ende des 1. Weltkrieges, Konstruktionen für das Ausland und die Jahre 1935 – 1945. Die deutschen U-Boote und ihre Werften (in German). I. Munich: Bernard & Graefe. ISBN 3-7637-5213-7.