In 1935, the South African Railways placed six Class 16E steam locomotives with a 4-6-2 Pacific type wheel arrangement in express passenger train service.

[1][2][3][4] With its 72 inches (1,830 millimetres) diameter coupled wheels, the Class 16E was considered the most remarkable Cape gauge express passenger locomotive ever built.

The coupled wheels were the largest ever used on a narrow-gauge locomotive, and it had a service weight and tractive effort equal to or exceeding most Pacifics outside North America.

[1][2][5] Watson experienced considerable difficulty keeping the axle loads within the permissible limits specified by the Chief Civil Engineer, resulting in the ashpan, cab, side running boards and several other parts being made of thinner material than usual.

Still, the axle load of 20 long tons 19 hundredweight (21,290 kilograms) was the heaviest of any engine or vehicle on the SAR at the time.

The connecting and coupling rods were fitted with floating bronze bushes and were made of special chrome-nickel alloy steel of fluted section.

[2][6] At 9 feet 3 inches (2,819 millimetres) above rail level, the Class 16E boiler centre-line was the highest-pitched on the SAR at the time.

To assist in keeping within the axle load limits, the ashpan was constructed of relatively thin anti-corrosive steel plates of a special heat-resisting quality.

[1][2][3] From here they hauled regular passenger trains, including the Orange Express, working north to Johannesburg and south to De Aar as well as across to Kimberley.

When air-conditioned lounge cars were added to trains like the Orange Express and Trans-Karoo, they were again considered incapable of handling the additional load and were eventually withdrawn from service in 1972.

[8] A 20c postage stamp depicting a Class 16E locomotive was one of a set of four commemorative postage stamps issued by the South African Post Office on 27 April 1983 to commemorate the steam locomotives of South Africa that were rapidly being withdrawn from service at the time.

The outline of a traditional SAR locomotive number plate was used as a commemorative cancellation for De Aar on the date of issue.