The 15F was a development of the Class 15E designed by AG Watson and is very similar in design. The 15F being fitted with Walschaerts valve gear rather than the Rotary Cam poppet valve system of the 15E. The 15E, itself, being a development of the Class 15CA.

The first class members, numbers 2902 to 2966, were delivered during 1938 and 1939 by Berliner Machinenbau, Henschel and Beyer Peacock and the next batch in 1944, numbers 2967 to 2996 by Beyer Peacock. A further sixty were delivered in 1945 and 1946 by North British (2997-3056) with final one hundred (3057-3156) also delivered by North British by 1948. From number 2967 the locomotives were fitted with vacuum brakes. Early locomotives did not have smoke deflectors but these were later fitted. Post war locomotives were also fitted with mechanical stokers, many being later fitted with the longer tender from scrapped Class 23 engines. Designed for main line freight and passenger services the 15F locos saw service over most of the South African rail system as well as Rhodesia where a number were on hire to Rhodesia Railways during 1978 and 1979.

The Class 15F locomotive weighs in at 178 tons with standard tender and 212.8 tons with a Class 23 tender. The length being 73 feet 6 inches (22,4m) and 87 feet 2 inches (26,56m) respectively.