The first 46 locomotives, with an operating boiler pressure of 140 pounds per square inch (965 kilopascals) and numbered in the range from 49 to 94, were placed in service during Milne's term.

Reid took over as Locomotive Superintendent in 1896, he continued to place further orders for another 58, numbered in the range from 91 to 148, but with the boiler pressure increased to 160 pounds per square inch (1,103 kilopascals).

The coal bunkers were also enlarged and the connecting rod big-ends were changed to the marine type to increase ground clearance.

The date of this improvement can be pinned to 1891 when the second batch of Michael Stephens’ Cape Government Railways (CGR) 5th Class 4-6-0 locomotives with their lengthened smokeboxes entered service.

This had such a profound effect on the boiler’s steaming ability that virtually every locomotive on the CGR and NGR had their smokeboxes extended.

In order to accomplish this, Hendrie raised the boiler's pitch by 4+1⁄2 inches (114 millimetres) and cut away the frame under the firebox to accommodate the wider grates.

[10] In the NGR era, the Class D fleet remained in service on the Natal mainline until they were eventually displaced by more modern locomotives.

They continued to serve well into the SAR era on the Dundee-Hlobane branchline, the Harrismith-Ladysmith section and on the north coast line to Empangeni.

[10] In 1915, shortly after the outbreak of the First World War, the German South West Africa colony was occupied by the Union Defence Forces.

Those following illustrate the short and long smokebox versions of the locomotive and some of the post-delivery changes which were made, such as the altered cab for better crew protection.