The class 15F was the most numerous class of steam locomotives of the SAR. It was the last in the series of the class 15 4-8-2 that was built from 1914 and was introduced in 1938 by W.A.J. Day. Like the class 15E of 1935, it had the Watson Standard type 3B boiler with a grate of 63 square feet and a heating surface of more than 3,000 square feet. This boiler was domeless in order to fit into the loading gauge with a maximum height of less than four metres.
The biggest change was that the 15F had Walschaerts valve gear, unlike the rotary cam poppet valve gear of the 15E. The dimensions of the drivers, cylinders and wheelbases were the same for both. So the class 15E also had drivers with a diameter of five feet and cylinders with a diameter of 24 inches and a stroke of 28 inches. It had roller bearings on the leading and trailing axles and the cab with a slanted front that was introduced by Watson.
The first 21 were built in 1938 in Germany, seven by the BMAG and 14 by Henschel. Later in the same year, North British built 44 which arrived in South Africa in 1939. After a production stop due to the war, 30 were built by Beyer, Peacock & Co. in 1944, followed by 60 built by North British in 1945. These were influenced by the new Chief Mechanical Engineer M.M. Loubser and had smoke deflectors and improved brakes. They were also fitted for the installation of mechanical stokers, which were installed a few years later. Also the earlier North British locomotives were rebuilt with stokers. The last and largest batch was also built by North British in 1946 and 1947 that had small changes in the boiler. It also had stokers from the start.
Originally, the locomotives were coupled to tenders with 14 or 15 tons of coal and 5,620 to 7,250 imperial gallons of water, depending on the batch. In the early seventies, all were still in service. In 1978, six were hired to Rhodesia. When the class 23 was withdrawn at the beginning of the eighties, the last batch of the 15F got their six-axle EW type tenders which carried 18 tons of coal and 9,200 to 9,500 gallons of water. But it did not take long until the 15F was also withdrawn. A large number went into preservation, mainly by Transnet Heritage Foundation. Around 60 survived the turn of the millennium, but some were scrapped in the following years.