The class 24 were the only 2-8-4 “Berkshire” locomotives in South Africa. They were designed by M.M. Loubser for use on branch lines with light rails of not much more than 40 pounds per yard or 20 kg per metre. There they had to replace the classes 6, 7 and 8 while still having a low axle load. 100 locomotives were built by North British in Scotland.

As a first for any locomotive in South Africa, they had integrally cast frames and cylinders. These, and the bogies of the tenders, were supplied by General Steel Castings of Eddystone, Pennsylvania. In the result, these locomotives had a maximum axle load of only eleven and a half tons. The tenders were of the Vanderbuilt type and had six axles, so that they also had an axle load of less than ten tons. Roller bearings were only present on the leading and trailing axles. 

55 of the 100 locomotives were used in the South West Africa region. When this region was dieselized in the early sixties, these locomotives came to other regions. Later others became surplus due to the electrification of lines. Their general withdrawals came in the eighties and 20 were preserved. Nine of these are now owned by the Transnet Heritage Foundation. No. 3620 was shipped to New Zealand in 1997 and went to Australia in 2001. Since 2021 it operates on the Bellarine Peninsular Railway in Victoria.