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 Most were still in service in the seventies and the last one was withdrawn in 1983.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.