 In 1926, No 17 was reboilered by the GWR and in this form was visually almost indistinguishable from the GWR 5600 Class.Thus the R (and closely related "Stephenson" M class, A, A1 and larger wheeled P classes) were designed for work on the Rhymney Railway, replacing smaller locomotives.When the smaller railway companies were forcibly merged into the GWR, these modern 0-6-2's were in generally good order (some were a few months old) and had proved successful.