|Laid down:||4 February 1908|
|Launched:||26 September 1908|
|Commissioned:||18 May 1909|
|Fate:||Sold, 5 December 1921|
|Class and type:||C-class submarine|
|Length:||142 ft 3 in (43.4 m)|
|Beam:||13 ft 7 in (4.1 m)|
|Draught:||11 ft 6 in (3.5 m)|
|Range:||910 nmi (1,690 km; 1,050 mi) at 12 kn (22 km/h; 14 mph) on the surface|
|Test depth:||100 feet (30.5 m)|
|Complement:||2 officers and 14 ratings|
|Armament:||2 × 18 in (450 mm) bow torpedo tubes|
Design and description
The C-class boats of the 1907–08 and subsequent Naval Programmes were modified to improve their speed, both above and below the surface. The submarine had a length of 142 feet 3 inches (43.4 m) overall, a beam of 13 feet 7 inches (4.1 m) and a mean draft of 11 feet 6 inches (3.5 m). They displaced 290 long tons (290 t) on the surface and 320 long tons (330 t) submerged. The C-class submarines had a crew of two officers and fourteen ratings.
For surface running, the boats were powered by a single 12-cylinder 600-brake-horsepower (447 kW) Vickers petrol engine that drove one propeller shaft. When submerged the propeller was driven by a 300-horsepower (224 kW) electric motor. They could reach 13 knots (24 km/h; 15 mph) on the surface and 8 knots (15 km/h; 9.2 mph) underwater. On the surface, the C class had a range of 910 nautical miles (1,690 km; 1,050 mi) at 12 knots (22 km/h; 14 mph).
The boats were armed with two 18-inch (45 cm) torpedo tubes in the bow. They could carry a pair of reload torpedoes, but generally did not as they would have to remove an equal weight of fuel in compensation.
Construction and career
C21 was laid down on 4 February 1908 by Vickers at their Barrow-in-Furness shipyard, launched on 26 September and was completed on 18 May 1909. During the war, the boat was generally used for coastal defence and training in home waters. C21 was sold for scrap on 5 December 1921.
- Gardiner & Gray, p. 87
- Harrison, Chapter 25
- Harrison, Chapters 3
- Harrison, Chapter 27
- Akermann, Paul (2002). Encyclopaedia of British Submarines 1901–1955 (reprint of the 1989 ed.). Penzance, Cornwall: Periscope Publishing. ISBN 1-904381-05-7.
- Colledge, J. J.; Warlow, Ben (2006) . Ships of the Royal Navy: The Complete Record of all Fighting Ships of the Royal Navy (Rev. ed.). London: Chatham Publishing. ISBN 978-1-86176-281-8. OCLC 67375475.
- Gardiner, Robert & Gray, Randal, eds. (1984). Conway's All the World's Fighting Ships: 1906–1921. Annapolis, Maryland: Naval Institute Press. ISBN 0-85177-245-5.
- Harrison, A. N. (January 1979). "The Development of HM Submarines From Holland No. 1 (1901) to Porpoise (1930) (BR3043)". Submariners Association: Barrow in Furness Branch. Retrieved 19 August 2015.