For heavy service on branch lines with a permitted axle load of less than 14 tonnes, D.A. Hendrie designed the 2-6-6-0 Mallet of the class MJ. It had a superheated boiler with a Belpaire firebox and Walschaerts valve gear. Ten were ordered from Maffei of Munich, of which the first two were delivered in 1914. But due to the outbreak of World War I, German manufacturers were not able anymore to deliver to South Africa. Instead, the eight missing locomotives were ordered from North British and delivered in 1917 and 1918. Meanwhile, the Montreal Locomotive Works delivered eight similar MJ1.

After the end of the war, Maffei felt that they had to fulfill the original order and delivered eight more, bringing the total number to 18. One of their tasks was pusher service on the Hex River Pass with a ruling grade of 1.8 percent and a five-mile section with 2.3 percent. In 1939, W.A.J. Day equipped this class and the MJ1 with a new common standard boiler. The last two MJ locomotives were scrapped in 1962 and were the last Mallets in active SAR service.