# SM UB-21

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 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 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

| Date | Name | Nationality | Tonnage | Fate |
| 5 May 1916 | Harald | Sweden | 275 | Sunk |
| 20 October 1916 | Lekna | Sweden | 204 | Sunk |
| 20 October 1916 | Randi | Norway | 467 | Sunk |
| 20 October 1916 | Svartvik | Sweden | 322 | Sunk |
| 21 October 1916 | Fritzöe | Norway | 641 | Captured as prize |
| 21 October 1916 | Grönhaug | Norway | 667 | Sunk |
| 22 October 1916 | London | Denmark | 184 | Sunk |
| 22 October 1916 | Thor | Norway | 372 | Sunk |
| 3 November 1916 | Pluto | Norway | 1,148 | Captured as prize |
| 16 February 1917 | Lady Ann | United Kingdom | 1,016 | Sunk |
| 17 February 1917 | Excel | United Kingdom | 157 | Sunk |
| 22 February 1917 | John Miles | United Kingdom | 687 | Sunk |
| 29 March 1917 | Bywell | United Kingdom | 1,522 | Sunk |
| 31 March 1917 | Norden | Norway | 776 | Captured as prize |
| 29 April 1917 | Victoria | United Kingdom | 1,620 | Sunk |
| 2 May 1917 | Rikard Noordrak | Norway | 1,123 | Sunk |
| 5 May 1917 | Edith Cavell | United Kingdom | 20 | Sunk |
| 6 May 1917 | Harold | Sweden | 1,679 | Sunk |
| 8 May 1917 | Batavier II | Netherlands | 157 | Captured as prize |
| 6 June 1917 | S.N.A. 2 | France | 2,294 | Sunk |
| 7 June 1917 | Sir Francis | United Kingdom | 1,991 | Sunk |
| 21 July 1917 | Trelyon | United Kingdom | 3,099 | Sunk |
| 22 July 1917 | Glow | United Kingdom | 1,141 | Sunk |
| 23 July 1917 | Vanland | Sweden | 1,285 | Sunk |
| 24 August 1917 | Springhill | United Kingdom | 1,507 | Sunk |
| 18 October 1917 | Amsteldam | United Kingdom | 1,233 | Sunk |
| 19 October 1917 | Gemma | United Kingdom | 1,385 | Sunk |
| 23 November 1917 | Ocean | United Kingdom | 1,442 | Sunk |
| 29 December 1917 | Inverness | United Kingdom | 3,734 | Damaged |
| 29 December 1917 | Patria | Russian Empire | 838 | Sunk |
| 30 December 1917 | Hercules | United Kingdom | 1,295 | Sunk |
| 25 March 1918 | Hercules | United Kingdom | 1,095 | Sunk |
| 8 May 1918 | Constantia | United Kingdom | 772 | Sunk |
| 10 May 1918 | Anboto Mendi | Spain | 2,114 | Sunk |
| 11 May 1918 | Gothia | Sweden | 1,826 | Sunk |
| 12 May 1918 | Haslingden | United Kingdom | 1,934 | Sunk |
| 4 July 1918 | Mentor | Norway | 539 | Sunk |
| 26 September 1918 | Paul | Belgium | 659 | Sunk |