In December 1927 and January 1928 the South African Railways placed two Class 18 three-cylinder steam locomotives with a 2-10-2 Santa Fe type wheel arrangement in service on the Witbank-Germiston coal line.

Collins DSO, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1922 to 1929, and built by Henschel and Son in Germany.

These were the most powerful non-articulated steam locomotives to see service on the SAR, with a tractive effort of 53,650 pounds-force (239 kilonewtons) at 75% boiler pressure and capable of hauling loads of 1,800 long tons (1,829 tonnes) over the ruling gradient of 1 in 100 (1%) on the Witbank-Apex section.

It was fired by a Duplex D.4 type mechanical stoker, operated by a four-cylinder steam engine on its Type HT tender, which had a coal capacity of 14 long tons (14.2 tonnes), a water capacity of 6,000 imperial gallons (27,300 litres) and a maximum axle load of 19 long tons 8 hundredweight (19,710 kilograms).

[2][6] To allow the locomotive to negotiate curves of 320 feet (98 metres) radius despite its long coupled wheelbase, the third and fourth pairs of driving wheels were flangeless.

The cylinder design was outdated and along with the lightweight motion and rods, contributed to them being uneconomical high-maintenance machines.

The complicated valve gear was not robust enough and frequently gave trouble owing to wear and breakage.

The Central South African Railways (CSAR) introduced Gould knuckle couplers on the rolling stock of its Limited Express and Imperial Mail passenger trains in 1904.