The Class 4 Mountain type locomotive was designed at the Salt River shops as a heavy mixed traffic locomotive by H.M. Beatty, the last Chief Locomotive Superintendent of the Cape Government Railways (CGR) [REF].
Soon after the South African Railways (SAR) locomotive renumbering and classification scheme was carried out in 1912, an order was placed with North British Locomotive Company for a further ten locomotives of this type, built to an altered design.