In 1917, the South African Railways placed seven Class K tank steam locomotives with a 4-6-4 Hudson type wheel arrangement in service.

Because of difficulties experienced in delivering them to the Philippines during the First World War as well as a critical wartime shortage of locomotives on the South African Railways (SAR), NBL eventually offered the seven locomotives for sale to the SAR.

The locomotives were superheated and their smokeboxes were equipped with Stone's Patent louvre spark arrestors.

They were the first locomotives in South Africa to be equipped with exhaust steam injectors, which were of the Davies and Metcalfe pattern.

As built, they had 12 inches (305 millimetres) diameter "bull's eyes" acetylene gas headlamps, powered from a generator affixed to the running board on the right hand side adjoining the smokebox.