They were designed by J. H. Hosgood and built by Sharp Stewart, & Co., Vulcan Foundry and Société Franco-Belge.

[1] The locomotive, though similar to the B class, differed in having an increased tank capacity of 1,630 gallons compared with the 1,400 gallons of the B class.

The purpose of this was to enable them to take a train of empty wagons from Cadoxton Yard to Trehafod Junction without the need to refill the tank.

Their main duty was to take loaded coal trains from Trehafod Junction, and the pits on the Brecon & Merthyr, to Cadoxton Yard and return either with the empty wagons or occasionally pit props from Barry Docks.

111 and 122, were used to take excursion trains from the Rhymney Railway to Barry for those visiting the National Eisteddfod held there in 1920.