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 The last ones were withdrawn in the eighties.

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.

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.

After the single 2-6-2+2-6-2 Modified Fairlie of class FC of the South African Railways, Colonel F.R. Collins specified a somewhat heavier variant that was again to be built by North British. The four locomotives were delivered in 1925 and were called class FD. They had direct competition from the class GD Garratt that had the same wheel arrangement.

In service it was found that the long rigid frame produced some problems. These included huge side overhangs when running through curves and oscillations of the water and coal tanks at speed. Also the pivot bearings had to support considerably higher weights due to the supplies being on the main frame. So ultimately the GD Garratts were more successful with 14 built. All FD locomotives were scrapped in 1949.

The South African Railways were looking for a powerful locomotive that could also be used on branch lines and that would be suitable for mixed service at a higher speed. Since at that time only articulated locomotives were to be procured and the required speed required leading bogies, the choice of wheel arrangement fell on the “Double Pacific” for the first time for the SAR, i.e. 4-6-2+2-6-4T.

The specifications were drawn up by Colonel F. R. Collins and sent to Hanomag in Germany, where 37 engines were made in 1927. In 1928, 18 more followed from Henschel and ten from Maffei. This made it the largest number of Garratts built for the SAR until 1953 when the GMA was introduced.

The origin of the locomotive could be seen from the sloped side walls of the driver's cab at the height of the windows. As the first South African Garratt, it had a bar frame that was now established in Germany. The chassis allowed a speed of 80 km/h, but the bearings of the trailing axles often overheated. The solution was to no longer store these axles in an inside but in an outside frame.

As planned, the locomotives were used in front of passenger and freight trains and on branch and main lines. The operational area of most locomotives was in Natal. A higher axle load was permitted on the line from Johannesburg to Mafeking, so that the quantity of coal was increased from 10 long tons to 11 long tons 10 cwt.

Four locomotives were sold to Mozambique as early as 1950, but the remaining machines remained in the SAR's inventory until 1972. At this point, however, not all of them were actively used and it only took until 1979 for the last remaining ones to be scrapped. In the meantime some had been sold to mine operators, most of them to the Enyati Railway. Some of these had received an air brake powered by a diesel-powered compressor. Two examples survive today and a third is being restored.

The South African class MF was a 2-6-6-2 Mallet originally ordered by the Central South African Railways (CSAR). They were built by ALCO and based on the MD prototype delivered in 1910, but were superheated. After delivery to South Africa in 1911 in parts, they were erected at Pretoria. Although the Union of South Africa had already been founded at this time, the first nine were still delivered to the CSAR and numbered 1015 to 1023. The last five were directly delivered to the SAR and called class MF No. 1629 to 1633. The first nine were renumbered 1619 to 1627.

While the first nine got an XS tender with ten tons of coal and 5,000 gallons of water, the last five got XM4 tenders with also ten tons of coal, but only 4,000 gallons of water. They were originally used in coal traffic between Witbank and Germiston where they hauled 1,600 tons on inclines of one percent. Between 1923 and 1925, six were simpled. Three of these came to the East London area whey they had to fight 2.5 percent inclines, but apparently without much success. All had been scrapped by 1939.