At the end of the war in 1902, the eight ex-OVGS locomotives came onto the roster of the Central South African Railways (CSAR), where they were renumbered in the range from 318 to 325. In 1904, the CSAR reboilered two of these locomotives, numbers 319 and 322, with larger boilers and Belpaire fireboxes which were equipped with Drummond tubes. This increased their heating surface by and, at a higher operating boiler pressure of , these two locomotives were able to easily haul the load of the next higher class. Since, by then, these locomotives were being withdrawn from mainline traffic, no more such reboilerings were carried out. When the Union of South Africa was established on 31 May 1910, the three Colonial government railways, the CGR, the Natal Government Railways and the CSAR, were united under a single administration to control and administer the railways, ports and harbours of the Union. Although the South African Railways and Harbours came into existence in 1910, the actual classification and renumbering of all the rolling stock of the three constituent railways was only implemented with effect from 1 January 1912. By 1912, sixteen of these locomotives survived, twelve on the CGR and four, including the two which had been reboilered, on the CSAR. They were considered obsolete by the South African Railways (SAR), designated Class 05 and renumbered by having the numeral 0 prefixed to their existing numbers. During 1914, at the outbreak of the First World War, military planners followed the example set by the British invading forces during the Second Boer War and identified a requirement for armoured trains. For this purpose, five Class 05 locomotives were specially protected with armour plate and named "Trafalgar", "Scot", "Erin", "Karoo" and "Schrikmaker". The armour-plating was fitted by the workshops in Pretoria, Bloemfontein and Salt River. Their engine numbers are not known, nor whether they were from this Class or the Class 05 of 1891 or both. In spite of being considered obsolete, some of the Class 05 locomotives survived as shunting engines in SAR service for another four decades, with some even getting reboilered while in SAR service. One confirmed example is no. 0506, which was still equipped with boiler no. 7244 of 1924 when it was withdrawn from service in the 1950s. When they were eventually withdrawn in 1953, the Class 05 locomotives were the last of the obsolete engines to be still in SAR service.