# SM UC-21

SM UC-21 was a German Type UC II minelaying submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. The U-boat was ordered on 29 August 1915 and was launched on 1 April 1916. She was commissioned into the German Imperial Navy on 12 September 1916 as SM UC-21.
In eleven patrols UC-21 was credited with sinking 98 ships, either by torpedo or by mines laid. They included the British hospital ship Donegal, which UC-21 torpedoed in the English Channel on 17 April 1917, killing 29 already wounded soldiers and 12 crew.
UC-21 disappeared after departing Zeebrugge for the Bay of Biscay on 13 September 1917.

## Design

Like all pre-UC-25 Type UC II submarines, UC-21 had a displacement of 417 tonnes (410 long tons) when at the surface and 493 tonnes (485 long tons) while submerged. She had a total length of 49.35 m (161 ft 11 in), a beam of 5.22 m (17 ft 2 in), and a draught of 3.65 m (12 ft). The submarine was powered by two six-cylinder four-stroke diesel engines each producing 250 metric horsepower (180 kW; 250 shp) (a total of 500 metric horsepower (370 kW; 490 shp)), two electric motors producing 460 metric horsepower (340 kW; 450 shp), and two propeller shafts. She had a dive time of 35 seconds and was capable of operating at a depth of 50 metres (160 ft).
The submarine had a maximum surface speed of 11.6 knots (21.5 km/h; 13.3 mph) and a submerged speed of 7 knots (13 km/h; 8.1 mph). When submerged, she could operate for 55 nautical miles (102 km; 63 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 9,430 nautical miles (17,460 km; 10,850 mi) at 7 knots (13 km/h; 8.1 mph). UC-21 was fitted with six 100 centimetres (39 in) mine tubes, eighteen UC 200 mines, three 50 centimetres (20 in) torpedo tubes (one on the stern and two on the bow), seven torpedoes, and one 8.8 cm (3.5 in) Uk L/30 deck gun. Her complement was twenty-six crew members.

## Summary of raiding history

| Date | Name | Nationality | Tonnage | Fate |
| 28 November 1916 | Clematis | United Kingdom | 22 | Sunk |
| 28 November 1916 | Lady of the Lake | United Kingdom | 91 | Sunk |
| 28 November 1916 | Vulcan | United Kingdom | 27 | Sunk |
| 28 November 1916 | HMD Pelagia | Royal Navy | 84 | Sunk |
| 30 November 1916 | Draupner | Norway | 1,126 | Sunk |
| 30 November 1916 | Eggesford | United Kingdom | 4,414 | Damaged |
| 30 November 1916 | Therese | France | 165 | Sunk |
| 1 December 1916 | King Bleddyn | United Kingdom | 4,387 | Sunk |
| 2 December 1916 | Demetrios Inglesis | Greece | 2,088 | Sunk |
| 2 December 1916 | Robinson | France | 186 | Sunk |
| 2 December 1916 | Uribitarte | Spain | 1,756 | Sunk |
| 3 December 1916 | Aiglon | France | 280 | Sunk |
| 3 December 1916 | Louise | France | 155 | Sunk |
| 3 December 1916 | Verdun | France | 184 | Sunk |
| 4 December 1916 | Pallas | Russian Empire | 1,202 | Sunk |
| 5 December 1916 | Nexos | Denmark | 1,013 | Sunk |
| 6 December 1916 | Gerona | Spain | 1,328 | Sunk |
| 7 December 1916 | Avristan | United Kingdom | 3,818 | Sunk |
| 8 December 1916 | HMT Dagon | Royal Navy | 250 | Sunk |
| 8 December 1916 | Falk | Norway | 1,379 | Sunk |
| 8 December 1916 | Marjolaine | France | 163 | Sunk |
| 8 December 1916 | Modum | Norway | 2,937 | Sunk |
| 17 December 1916 | Margaret | United Kingdom | 54 | Sunk |
| 18 January 1917 | HMS Ferret | Royal Navy | 778 | Damaged |
| 19 January 1917 | Joseph Rosalie | France | 138 | Sunk |
| 19 January 1917 | Marietta Di Giorgio | Norway | 988 | Sunk |
| 19 January 1917 | Tremeadow | United Kingdom | 3,653 | Sunk |
| 20 January 1917 | Kisagata Maru No. 3 | Japan | 2,588 | Sunk |
| 20 January 1917 | Jotunfjell | Norway | 2,492 | Damaged |
| 21 January 1917 | Victoire | France | 290 | Damaged |
| 21 January 1917 | Leontine | France | 124 | Sunk |
| 21 January 1917 | Saint Pierre | France | 127 | Sunk |
| 22 January 1917 | Bearnais | France | 301 | Sunk |
| 22 January 1917 | Precurseur | France | 364 | Sunk |
| 22 January 1917 | Steinmachos | Greece | 1,175 | Sunk |
| 24 January 1917 | Dan | Denmark | 1,869 | Sunk |
| 24 January 1917 | Gladiateur | France | 23 | Sunk |
| 24 January 1917 | Loire III | France | 27 | Sunk |
| 24 January 1917 | Marie 3 | France | 25 | Sunk |
| 24 January 1917 | Quebec | France | 3,346 | Sunk |
| 24 January 1917 | Vega | Denmark | 195 | Sunk |
| 25 January 1917 | Myrdal | Norway | 2,631 | Sunk |
| 1 February 1917 | Sainte Helene | France | 2,128 | Sunk |
| 10 February 1917 | Beechtree | United Kingdom | 1,277 | Sunk |
| 11 February 1917 | Dernes | Norway | 738 | Sunk |
| 12 February 1917 | Nordcap | Norway | 332 | Sunk |
| 13 February 1917 | Progreso | Norway | 1,620 | Sunk |
| 14 February 1917 | Longscar | United Kingdom | 2,777 | Sunk |
| 14 February 1917 | Mar Adriatico | Spain | 2,410 | Sunk |
| 15 February 1917 | Aline | France | 30 | Sunk |
| 15 February 1917 | Marion Dawson | United Kingdom | 2,300 | Sunk |
| 16 February 1917 | Niobe | France | 1,319 | Sunk |
| 16 February 1917 | Pollcrea | United Kingdom | 1,209 | Damaged |
| 17 February 1917 | Cabo | Norway | 1,254 | Sunk |
| 17 February 1917 | Silene | France | 171 | Sunk |
| 18 February 1917 | Triumph | United Kingdom | 52 | Sunk |
| 19 February 1917 | Rutenfjell | Norway | 1,844 | Sunk |
| 10 March 1917 | Asbjørn | Norway | 3,459 | Sunk |
| 12 March 1917 | Alice Charles | France | 41 | Sunk |
| 12 March 1917 | Arethuse | France | 40 | Sunk |
| 13 March 1917 | Girda | Norway | 1,824 | Sunk |
| 13 March 1917 | Vivina | Spain | 3,034 | Sunk |
| 14 March 1917 | Blaamanden | Norway | 954 | Sunk |
| 14 March 1917 | La Marne | France | 133 | Sunk |
| 15 March 1917 | Eugene Robert | France | 98 | Sunk |
| 15 March 1917 | Fleur D’Esperance | France | 24 | Sunk |
| 15 March 1917 | Frimaire | United Kingdom | 1,778 | Sunk |
| 15 March 1917 | Petit Jean | France | 21 | Sunk |
| 16 March 1917 | Anais | France | 130 | Sunk |
| 16 March 1917 | Madeleine Davoust | France | 148 | Sunk |
| 16 March 1917 | Ronald | Norway | 3,021 | Sunk |
| 18 March 1917 | Illinois | United States | 5,225 | Sunk |
| 17 April 1917 | HMHS Donegal | Royal Navy | 1,885 | Sunk |
| 19 April 1917 | Cilurnum | United Kingdom | 3,126 | Sunk |
| 20 April 1917 | Georgios | Greece | 3,124 | Sunk |
| 21 April 1917 | Emile Et Charlotte | France | 41 | Sunk |
| 21 April 1917 | Ville De Dieppe | Norway | 1,254 | Sunk |
| 22 April 1917 | Capenor | United Kingdom | 2,536 | Sunk |
| 22 April 1917 | Percy Birdsall | United States | 1,127 | Sunk |
| 22 April 1917 | Valerie | Norway | 2,140 | Sunk |
| 24 April 1917 | Barnton | United Kingdom | 1,858 | Sunk |
| 25 April 1917 | Baigorry | France | 2,161 | Sunk |
| 26 April 1917 | Boy Denis | United Kingdom | 41 | Sunk |
| 22 May 1917 | Jeune Albert | France | 25 | Sunk |
| 23 May 1917 | Harwood Palmer | United States | 2,885 | Sunk |
| 23 May 1917 | Lesto | United Kingdom | 1,940 | Sunk |
| 26 May 1917 | Aristides | Greece | 2,179 | Sunk |
| 26 May 1917 | Norhaug | Norway | 1,245 | Sunk |
| 27 May 1917 | Efstathios | Greece | 3,847 | Sunk |
| 28 May 1917 | Hiram | Norway | 598 | Sunk |
| 28 May 1917 | Urna | Norway | 2,686 | Sunk |
| 28 May 1917 | Waldemar | Norway | 1,267 | Sunk |
| 30 May 1917 | Sørland | Norway | 2,472 | Sunk |
| 2 June 1917 | Tonawanda | United Kingdom | 3,421 | Damaged |
| 7 June 1917 | Hafnia | Denmark | 1,619 | Sunk |
| 29 June 1917 | Lauwerzee | Netherlands | 47 | Sunk |
| 4 July 1917 | Bestevaer | Netherlands | 1,044 | Sunk |
| 4 July 1917 | Roelfina | Netherlands | 148 | Captured as prize |
| 11 July 1917 | Coquimbo | France | 1,759 | Sunk |
| 15 August 1917 | Phoebe | France | 3,956 | Sunk |
| 17 August 1917 | Pontoporos | Greece | 4,049 | Sunk |
| 19 August 1917 | Therese & Marie | France | 1,615 | Sunk |
| 31 August 1917 | Marques De Mudela | Spain | 1,930 | Sunk |
| 16 September 1917 | Ann J. Trainer | United States | 426 | Sunk |
| 23 September 1917 | St. Dunstan | United Kingdom | 730 | Sunk |