[1] For surface running, the boats were powered by a single 12-cylinder[2] 600-brake-horsepower (447 kW) Vickers petrol engine that drove one propeller shaft.

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).

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.

[4] C20 was laid down on 1 June 1908 by Chatham Royal Dockyard, launched on 27 November 1909, and completed on 31 January 1910.

During World War I, the boat was generally used for coastal defence and training in home waters.