The Rhymney R class was a class of 0-6-2T steam locomotive introduced into traffic in 1907 designed by the railway's engineer Hurry Riches. These were substantial sized tank locomotives, and weighed 67 long tons (75 short tons; 68 t) (62 long tons or 69 short tons or 63 t after rebuilding) and were 37 feet (11.28 m) in length. There were initially three locos in the class augmented to five in 1909. They were built by Robert Stephenson, though in 1921 Hudswell Clarke built four and Beyer, Peacock and Company contributed a further six.