The 4-8-2 locomotive of the class 12A was the last design by D.A. Hendrie for the South African Railways. It was based on the class 12 that had been introduced before World War I. The biggest change was that the area of the firebox was enlarged by 30 percent. All in all, they had the maximum size that was possible for a Mountain locomotive on cape gauge.

Between 1919 and 1929, North British built 48 and Henschel built 19 more. At the beginning, they were used for coal trains on the line between Witbank and Germiston. Later they were also used for passenger trains and spread over all South Africa. Starting in 1943, a total of 44 were rebuilt to class 12AR. Since there was no Watson standard boiler in a suitable size, they got a completely new boiler.

All in all, both the unrebuilt class 12A and the rebuilt class 12AR were reported to be very free steaming and powerful for a cape gauge Mountain. Between 1947 and 1953, North British built eight similar locomotives without superheater for industrial operators. In SAR service, the remaining class 12A and 12AR locomotives had all been moved to shunting service by 1977. The last ones were withdrawn in the eighties.

The class 15A was a 4-8-2 mixed traffic locomotive designed by D.A. Hendrie as a successor of the class 15. It was the last plate frame locomotive of this wheel arrangement designed by him and had the goal to address the overly long tubes of the class 15. The solution was to fit the Belpaire firebox with a combustion chamber that decreased the length of the tubes. This also enlarged the heating surface from 155 to 192 square feet. 

The first 13 were built by North British in 1914 with a narrow cab. The later ones got a wider cab and a modified form of the running boards. Additionally, they had no flanges on the first set of driving wheels to improve their running characteristics on lines with sharp curves like the Hex River Pass. In total, North British had built 53 locomotives by 1920. Beyer, Peacock delivered 30 more in 1920 and 1921, followed by 15 more from North British in 1921. The last batch of 21 was delivered by Maffei in 1925.

The first five also had steel fireboxes to decrease the weight on the trailing axle, but these had problems when they were fed with water of poor quality. So their fireboxes were changed to copper and all others were built with copper fireboxes from the start. No. 2100, the last locomotive from the Maffei batch, was built with Lentz rotary cam poppet valves which were later rebuilt to piston valves operated by Walschaerts valve gear, similar to all other class members.

In passenger traffic, the class 15A could reduce the travelling time of the Union Limited by 2.5 hours. In the thirties they became class 15AR when they were fitted with Watson standard No. 2A boilers with round-topped fireboxes and no combustion chambers. Initially they got copper fireboxes, but later rebuilds used steel fireboxes. Although these improved the standardization among the classes of the SAR, but reduced the steaming capacity with a firebox heating surface of only 142 square feet. They also had the distinctive cabs with slanted fronts known from other locomotives. In the early eighties most were used in shunting service, while some were hired out to Swaziland. After their withdrawals few years later, twelve were preserved.

The class 15E was designed by A.G. Watson as a further development of the class 15C Mountain for mixed service. At that time, in 1935, Watson introduced several standardization features for the classes 15E, 16E and 19C, which had been ordered simultaneously. All of these classes featured rotary cam poppet valves. The 16E Pacific and the 15E Mountain had the same 24-by-28-inch cylinders. The Mountain was equipped with the Watson Standard 3B boiler, in contrast to the shorter 3A boiler on the Pacific. Both had virtually the same firebox with a grate area of 63 square feet, 206 square feet in the walls, and 26 square feet in arch tubes.

The first 20 were built in 1935 by Robert Stephenson & Hawthorns. In the following year, Henschel built 16 and BMAG built eight. The German locomotives were three-quarters of a ton lighter. They were nicknamed “Bongols” and initially hauled the heaviest and most important trains. Soon, the Class 15F was built in larger numbers with Walschaerts valve gear. In the 1950s, both were pushed into secondary service and replaced by the classes 25 and 25NC. The last ones were taken out of service in 1973, though some were sold to Rhodesia or Mozambique. 2878 is preserved by the Transnet Heritage Foundation in Bloemfontein.

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.

Since the axle load of the SAR class 19 was still too high for some branch lines, Col F.R. Collins designed the lighter class 19A. Changes included a smaller boiler, a cylinder diameter of 19.5 instead of 21 inches and a driver diameter of 51 instead of 54 inches. In total, this made a weight saving of four tons. Additionally, the axle load could be changed by setting of a pin in the suspension of the trailing axle. 

36 were built in 1929 by the Swiss SLM. As early as in the middle of the thirties, five got a standard boiler developed by A.G. Watson and were designated class 19AR. Two of these got domeless boilers. The SAR used the classes 19A and 19AR until 1977. After this, a few were sold for industrial service. Three 19 and two 19A have been preserved.

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 with the standard domed boiler, 40 by Borsig and 15 by Škoda in Czechoslovakia. 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 were 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 11^th class. Henschel managed to get two more orders which were built between 1951 and 1953, including 21 Rhodesia Railways 19^th 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 against 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.

The class 23, designed by W.A.J. Day and introduced in 1938, was the last 4-8-2 locomotive built for the SAR. It was similar to the class 15F and used the same Watson Standard No. 3B boiler. Both were also the heaviest classes of the SAR with this wheel arrangement, while the class 19D that had been introduced in 1937 was much lighter. While the 15F had a driver diameter of 60 inches, the 23 was originally planned with a diameter of 66 inches. As this would have caused problems with length and curve negotiation, a diameter of 63 inches was chosen instead. To reduce the negative effect on the tractive effort, the boiler pressure was increased from 210 to 225 psi. 

A stoker was used to fill the grate of 63 square feet. The first driving axle had one inch of lateral play, while the third one had thinner flanges. The first order built in 1938 included seven locomotives built by BMAG and 13 built by Henschel. Another order was built in the following year that included 31 from BMAG and 85 from Henschel. To be able to cross the Karoo desert, they were provided with six-axle EW type tenders with 9,200 imperial gallons of water and 18 tons of coal. The tenders of the second batch could even hold 9,500 gallons thanks to a revised weight distribution.

After World War II, all locomotives of this class received elephant ear smoke deflectors inspired by the German design. They were used in passenger and freight service as well, but from 1953 their most important passenger services were taken over by the classes 25 and 25NC. From the late fifties, they also hauled manganese ore trains of up to 2,700 tons. Most were still in service in the seventies and the last one was withdrawn in 1983. Two have been preserved, both built by BMAG and both on static display.

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.

In the desert areas of the Karoo and Kalahari, the large water requirements of powerful steam locomotives posed a major problem for the SAR. The contract for the development of a 4-8-4 locomotive and a condensation tender went to Henschel in Kassel. At the same time, the class 25NC was developed without a condenser. The prototype was built by Henschel and taken to North British in Scotland, where the rest was built. For the conditions of the Cape Gauge, these locomotives were very large and powerful.

In order to provide sufficient draft for the fire, the blower had to be particularly powerful. This did not work with a steam jet as usual, but with a fan driven by a turbine. When running under load, no exhaust beats could be heard, but instead the whine of the turbine.

In order to protect the fan from damage caused by solid objects in the smokebox, it was provided with a banjo-shaped extension. The fan still had to be changed later because it wore out very quickly. Instead of an injector, a turbo pump had to be used to feed the boiler because the condensed water was still at a very high temperature.

Timken roller bearings were installed everywhere, which caused problems in the early days. Oil was thrown from the bearings on the coupling rods against the underside of the boiler, which then dripped onto the wheel tires and made the locomotive more prone to slipping. This could only be remedied after the bearings on a large part of the locomotives had been replaced with ones from SKF and after Timken had repaired the remaining bearings.

The operations took place on the non-electrified lines in the desert areas in front of all types of trains. All in all, the locomotives achieved a range of around 500 miles or 800 km with one water filling, but at the expense of extensive maintenance. The fans in the smokebox and on the tender were particularly important here.

Therefore, between 1973 and 1980, 87 of the 90 class 25 locomotives were rebuilt into Class 25NC. The long tenders with a round water tank and no condenser were now called “Worshond Tender” because of their appearance, which stands for “Dachshund” and literally means “sausage dog”. They were retired around 1990 when all remaining steam locomotives were replaced by diesel and electric locomotives.

Based on the 4-6-2 Karoo class locomotives, the Cape Government Railways ordered four “Enlarged Karoo” locomotives also designed by H.M. Beatty shortly before the founding of the South African Railways. In comparison to the original Karoo, they had a higher pitched boiler, larger wheels and larger cylinders. In contrast to earlier CGR locomotives, they had a Belpaire firebox and no round-topped one. They were only delivered in 1912 directly to the SAR and called class 5, while the original Karoo locomotives were called class 5A and 5B.

In 1935, in a time when many SAR locomotives got superheated A.G. Watson standard boilers, only one Enlarged Karoo got this boiler. In this process it was renamed class 5R it also got larger drivers, larger cylinders and a lower boiler pressure. While the unrebuilt locomotives were relegated to secondary services in 1928 and withdrawn in 1942, the single class 5R locomotive survived until 1969. For a long time it had been in use in suburban services around Cape Town and was regularly operated at 60 mph (97 km/h) until the mid-sixties.