The class MH of the South African Railways consisted of five 2-6-6-2 Mallets built in 1915 for coal traffic on the line between Witbank and Germiston in Transvaal. There they complemented the class MJ 2-6-6-0 Mallets which had been in service just for a year. Designed by D.A. Hendrie, their parts were manufactured by North British and assembled in the Salvokop shops in Pretoria.

They were superheated from the start, had a round-topped firebox and were initially set for a pressure of 200 psi, which was later reduced to 180 psi. When delivered, they were the biggest and most powerful locomotives which had ever been built for cape gauge. On an incline of 1.05 percent, they were rated for 500 tons. Although they were outperformed by the class GA Garratts delivered from 1920, they remained in service until 1940.