The difficulties regarding accessibility to the inside cylinder, inherent with the cramped space allowed for a third cylinder by the Cape gauge, probably also served as a deterrent and only the one locomotive was therefore built. The Compound Karoo was placed in service in the Karoo, on the section between Beaufort West and De Aar. It performed well, provided the centre high-pressure big-end bearings were given adequate care and frequent lubrication. When the Union of South Africa was established on 31 May 1910, the three Colonial government railways (CGR, Natal Government Railways and Central South African Railways) 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 were only implemented with effect from 1 January 1912. In 1912, the Compound Karoo was designated Class Experimental 1 on the South African Railways and renumbered 764. It continued to work passenger trains through the Karoo until it was withdrawn from service in 1933 and scrapped.