The class 15CA was developed from the class 15C mixed-traffic 4-8-2 locomotive which was the first in the line of the big boilered Mountains of the SAR. The major problem was that the twelve class members suffered from frequent frame cracks. Col. F.R. Collins solved the issue by redesigning the frame under the firebox, what resulted in the 15CA. Apparently, the “A” in the class designation stood for their manufacturer ALCO, while the original class 15C, built by Baldwin, later became class 15CB. The first 23 were delivered in 1926. In 1929 and 1930, Baldwin, Breda and North British delivered 61 more.
When they were built, all had a driver diameter of 57 inches and most had cylinders with a diameter of 23 inches and a stroke of 28 inches. Only the last 18, built by NBL, had a cylinder diameter of 24 inches. Later also all others had their cylinder diameter increased to 24 inches. The whole class soon received new tyres with a outside diameter of 60 inches. As this decreased their starting tractive effort, the boiler pressure was increased from 200 to 210 psi to offset this. In the early forties, three locomotives received new boilers developed by M.M. Loubser.
As mixed traffic locomotives, the class 15CA was used for day and night passenger and freight trains. In later years, nearly half of the class was used for shunting at Kaserne and Germiston. Two were sold to the Rustenberg Platinum Mines and one to South Witbank Colliery. Today 16 are still existing, most of them under administration of the Transnet Heritage Foundation. Six are at the MeMysons International Steam Locomotive Preservation Trust (MISLPT).
