In 1900, the Imperial Military Railways placed 25 Cape 7th Class 4-8-0 Mastodon type steam locomotives in service.

[1][2][3][4] After the outbreak of the Second Boer War in 1899, control of all railways in the Cape of Good Hope and the Colony of Natal remained in the hands of their civil staff, but now working in co-operation with the invading British military.

As possession was gradually obtained of the lines of the Orange Free State and the Zuid-Afrikaansche Republiek, the Oranje-Vrijstaat Gouvernement-Spoorwegen (OVGS) and the Nederlandsche-Zuid-Afrikaansche Spoorweg-Maatschappij (NZASM) were combined into the Imperial Military Railways (IMR).

[1] Because of the damage caused during hostilities and the transportation demands of the British armed forces, a shortage of locomotives developed.

In 1900, the IMR placed an order with Neilson, Reid and Company for 25 Cape 7th Class locomotives which were numbered in the range from 106 to 130 upon delivery.

[1][5] Also in 1900, three Cape 7th Class locomotives which had been ordered before the war by the Pretoria-Pietersburg Railway (PPR), were intercepted by the IMR and placed in service.

[1] After the cessation of hostilities on 1 June 1902, the IMR was transferred to civil control on 1 July 1902 and renamed the Central South African Railways (CSAR).

[1] In 1906, three of these locomotives, CSAR numbers 384, 389 and 393, were sold to the Natal Government Railways (NGR), who used them to work on the Harrismith-Bethlehem section in the Orange River Colony (ORC) on the mainline from Ladysmith to Bloemfontein.

[1][2][4][8] Two locomotives which returned to South Africa from Rhodesia c. 1915 were incorrectly classified, possibly as a result of their records getting exchanged in an apparent administrative error.

The reboilered locomotive was reportedly also equipped with Drummond tubes in its firebox, but these were found to be unsatisfactory and were soon removed.

On the two versions of 5th Class, the fact that they were gradually being replaced on mainline work made the cost of reboilering and modifying the frame unjustifiable.

On the reboilered 7th Class locomotive, problems were experienced with overloaded bearings and loose crank pins which led to a decision not to convert any of the others.

[3][9] In 1915, shortly after the outbreak of the First World War, the German South West Africa colony was occupied by the Union Defence Forces.

Most remained in SWA and were only transferred back to South Africa when the Class 32-000 diesel-electric locomotives replaced them in 1961.

The company worked the teak forests which stretched 100 miles (160 kilometres) to the northwest of Livingstone, where it built one of the longest logging railways in the world to serve its sawmill at Mulobezi.