This was the last iteration in the class 19 series of branch line 4-8-2 locomotives with a lighter axle load than the class 15. Designed by W.A.J. Day, it was based on the 19C, but had Walschaert valve gear instead of rotary cam poppet valves and had improvements in the steam passages which led to the cylinders. It had the same Watson Standard No. 1A boiler that was also fitted to the class 19C and rebuilt class 19R, 19AR and 19BR locomotives. Like many South African locomotives of this era, the first batches were built in Germany.
In 1937, 20 came from Krupp which had domeless boilers, and 20 more from Borsig with standard domed No. 1A boilers. In the following year, 40 more were built by Krupp, 40 by Borsig and 15 by Škoda in Czechoslovakia, all with the standard domed boiler. Due to an uneven weight distribution, the Škoda locomotives had 15.5 tons on the fourth driving axle, while the others had only 13 to 14 tons on their heaviest axle. After no further locomotives had been built during World War II, further orders went to British manufacturers. 50 came from Robert Stephenson & Hawthorns in 1947 and 50 more from North British in 1949. This brought the total number of class 19D locomotives built for the SAR to 235, making it the second most numerous SAR locomotive after the class 15F with 255.
In the following years, more were built for other countries. North British built six in 1951 for the Benguela Railway in Angola which became their 11th class. Henschel managed to get two more orders which were built between 1951 and 1953, including 21 Rhodesia Railways 19th class locomotives and two for the Nkana copper mine. North British completed the last four in 1955 which were destined for the Wankie coal mine, also in Rhodesia. This brought the total number of this design to 268, more than the class 15F. Actually 269 were built, since one from the 1947 RSH batch was lost to the sea and was replaced by a new one, paid for by the insurance company.
Although designed for branch lines with a low axle load, most class 19D locomotives were delivered with four-axle MT-type tenders with twelve tons of coal and 6,000 gallons of water. While the locomotives (apart from the ones built by Škoda) had a maximum axle load of less than 14 tons, these tenders had an axle load of 16.5 tons and thus prevented the use on exactly the lines for which these locomotives were built. So most of the class now received MP1-type tenders which had only ten tons of coal and 4,250 gallons of water, but an axle load of less than 14 tons. The last batch built by North British was delivered with Vanderbilt-style MX tenders with six axles. These carried twelve tons of coal and 6,500 gallons of water.
As the class 19D was used throughout South Africa, the tenders of individual locomotives were exchanged several times depending on the region they were used. They stayed in service until the end of steam and were replaced by diesel and electric locomotives. When David Wardale was planning to build his 4-8-4 high-performance steam locomotive in the seventies, he got No. 2644 to test a variety of his innovations before he totally rebuilt class 25NC no. 3450. Around 50 were preserved, nearly half of them by Transnet Heritage Foundation. Some are still operational.
