Thirty-six Class 19A engines were delivered by Swiss Locomotive and Machine Works (SLM) of Winterthur in 1929, numbered in the range from 675 to 710.

Collins DSO, Chief Mechanical Engineer (CME) of the South African Railways (SAR) at the time, redesigned the Class 19 to achieve a lighter axle loading by reducing the coupled wheel diameters from 54 to 51 inches (1,372 to 1,295 millimetres), reducing the cylinder diameter from 21 to 19+1⁄2 inches (533 to 495 millimetres) and by using a slightly smaller boiler.

[1][2][5] The reduction in axle load was to suit some of the lighter branch lines and, as part of the weight reduction, the Class 19A was delivered with a new smaller Type MP tender with a fuel capacity of 9 long tons 4 hundredweight (9.3 tonnes), a water capacity of 4,250 imperial gallons (19,300 litres) and a maximum axle load of 12 long tons 17 hundredweight 2 quarters (13,080 kilograms).

The axle load weights as listed for the Class 19A are with the trailing truck compensating beam pin in the leading of the three holes.

The axle load weights as listed for the Class 19AR are with the trailing truck compensating beam pin in the centre hole.

[1][3][4] From the 1930s, many serving locomotives were reboilered with a standard boiler type designed by then CME A.G. Watson as part of his standardisation policy.

685, depicted alongside as it is displayed in the Outeniqua Transport Museum in George, is incorrectly inscribed "19AR" since that locomotive was retired without being reboilered with a Watson Standard boiler.

The engine was photographed, still with its original boiler, as late as April 1970, fifteen years into electrification and dieselisation of the SAR and with steam traction already largely relegated to shunting and pickup work.