South African locomotive numbering and classification

The Union of South Africa was established on 31 May 1910 in terms of the South Africa Act, which unified the former Cape Colony, Natal Colony and the two colonised former republics, the Transvaal and the Orange Free State. One of the clauses in the Act required that the three Colonial Government railways, the Cape Government Railways, the Natal Government Railways and the Central South African Railways, also be united under one single administration to control and administer the railways, ports and harbours of the Union. While the South African Railways (SAR) came into existence in 1910, the actual classification and renumbering of all the rolling stock of the three constituent railways required careful planning and was only implemented with effect from 1 January 1912.

Each of the component railways of the new South African Railways (SAR) used their own locomotive classification and numbering system. Nearly two years after the establishment of the Union of South Africa, on 1 January 1912, a carefully planned reclassification and renumbering scheme was brought into operation. Most of the locomotives of the Cape Government Railways (CGR), Natal Government Railways (NGR) and Central South African Railways (CSAR) were renumbered into the SAR roster and, with some exceptions, reclassified. Locomotives which retained their old classifications were mostly from the CGR and CSAR, since the SAR more or less followed the CGR's classification system, while the CSAR's was similar to that of the CGR.

The SAR used different classification systems for its steam locomotives, according to locomotive type. Tender locomotives, shunting locomotives excluded, were classified numerically, while tank, articulated and shunting locomotives were classified using letters of the alphabet. All 3 ft 6 in (1,067 mm) steam locomotives were numbered sequentially, beginning with number 1, but not necessarily in the order of their new 1912 classifications.

Tender type steam locomotives, shunting locomotives excluded, were arranged in numerical classes (Classes 1 to 21 and 23 to 26), while variations within classes were indicated by an alphabetical suffix, for example Classes 12, 12A and 12B. Locomotives reboilered with Watson Standard boilers (see below), were reclassified with an additional "R" suffix, for example Classes 12R and 12AR. Some engines were rebalanced to redistribute their axle loadings for either mainline or lighter rail branchline service and were reclassified with an additional "M" (for mainline) or "B" (for branchline) suffix, for example Classes 14CRM and 14CRB.

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