Between 1937 and 1949, the South African Railways placed 235 Class 19D steam locomotives with a 4-8-2 Mountain type wheel arrangement in service.

Soft grease lubrication was used throughout for the motion gear, except the piston rods, valve spindles and main crossheads which were oil-lubricated.

Two four-feed sight lubricators, arranged in the cab, supplied oil to the steam chests and cylinders.

1A boiler, fitted with Ross Pop safety valves and set at 200 pounds per square inch (1,379 kilopascals) pressure.

The regulator was of the multiple-valve type, with the valves arranged on the saturated steam side of the superheater header in accordance with SAR practice.

In the process of locomotives undergoing major overhauls, these twenty Krupp-built domeless boilers migrated between engines during subsequent years.

In line service, type MX Torpedo tenders were usually preferred for their larger coal and water capacities.

[3] Tasks varied from mainline local and international passenger trains on the section between Warrenton and Mafeking en route between South Africa and Northern Rhodesia via Bechuanaland and Southern Rhodesia, to secondary and branch line duties and in later years as shunting engines.

SAR Class 19D locomotives were also hired out for shunting work to the Rhodesia Railways for use at Beit Bridge and to Mozambique for use at Lourenco Marques.

[3] Other Southern African railways and some industries also purchased locomotives built to the Class 19D design.

[9] These locomotives were wood- or coal-fired, depending on where they were operating, and had tenders with slatted frames installed on top of the bunker to increase their fuel capacity when wood was used.

[18] By June 1975, only three were left in service, all allocated to the Bulawayo shed, but with two out-stationed at Mafeking in South Africa.

[12][16] In 1955 four more without superheating and numbered in the range from 1 to 4 were built to the design of the Class 19D by NBL for the Wankie Colliery in Southern Rhodesia.

By the late 1980s, some of them were already at work at Dunn's, Saiccor, Loraine Gold Mine and Bamangwato Concessions Ltd. (BCL) in Botswana, and more were to follow.

As late as 2011, two Class 19Ds which had been used on the Vaal Reefs Gold Mine in the 1980s until they were retired and dumped at Jan Kempdorp where they stood unprotected for about twenty years, were bought by BCL Selebi-Phikwe.

However the mine closed in late 2016 putting the entire fleet out of work and now up for sale (December 2018).

[3][22] A gas producer combustion system (GPCS) and dual Lempor exhaust were installed, along with some other small improvements.

[3] The modifications improved the locomotive's steaming rate and enabled it to achieve significantly higher power and significantly lower fuel consumption than other unmodified Class 19D locomotives, the coal savings and increased output being in the order of 20% to 25%.

The success of this experiment convinced the SAR management at the time of the viability of the project which culminated in the Class 26 Red Devil.

Batch code symbols for the weight specifications as defined in the infobox are included in the "Notes" column.