The 4-6-4+4-6-4 was the fifth most common Garratt wheel arrangement, with 84 locomotives constructed, 74 by Garratt patent owner Beyer, Peacock & Company between 1936 and 1950 and ten under sub-contract from Beyer, Peacock by Belgian manufacturer Société Franco-Belge in 1952.

They remained in use into the 1980s, but their ultimate post-civil war fate is unclear and all of them are presumed to have been scrapped.

Only the South African Class GMA 4-8-2+2-8-4 Double Mountain was more numerous at 120 locomotives.

[3] The 15th class was a development of the RR 16th class 2-8-2+2-8-2 Garratts, to meet a requirement for a locomotive with a larger driving wheel diameter for higher speed train service on the more level parts of the railway.

The last forty locomotives were designated as the 15A class, since they had boilers with the rated pressure increased from 180 to 200 pounds per square inch (1.24 to 1.38 megapascals).