The class B of 1909, also called “Hendrie D” after its designer, was the first 4-8-2 “Mountain” locomotive with a firebox behind all driving axles. It was intended for heavy coal traffic on the upper Natal mainline and needed a large firebox to sustain high power. Starting from the previous class B rebuilt to a 4-8-2 that had its firebox still over the last two pairs of drivers, Hendrie created an auxiliary frame behind the last set of drivers that made space for a deep, wide Belpaire firebox with a grate of 34 square feet or 3.16 square metres.

The boiler was the biggest in South Africa at that time and still remained the biggest saturated one in later years. The locomotives were fitted with slide valves and a Hendrie steam reverser. Although they had a driver diameter of only three feet and 9 1/2 inches (1,156 mm), they were also suited for passenger service and had no problems with speeds of 50 mph or 80 km/h. In coal service, test runs showed that they could haul trains of more than 1,100 tons.

The first five were built by North British in 1909. These had TJ type tenders with a water capacity of 3,500 imperial gallons and 6 tons of coal. 25 more followed in 1910 which had TM type tenders with 4,000 gallons and 8.25 tons, respectively. The SAR designated them class 3. In the thirties, 29 were fitted with a superheated standard boiler designed by A.G. Watson. They now had piston valves and were designated class 3R. From the sixties, the remaining locomotives were used in shunting and pickup service. The last one was withdrawn in 1974.