Because of the difficulties experienced by the usual British and German suppliers to build new locomotives during the First World War, orders for the Class MJ1 2-6-6-0 Mallet articulated compound steam locomotive were placed with Montreal Locomotive Works (MLW) in Canada. The locomotive was designed by MLW, based on the specifications for the Class MJ Mallet which was designed by D.A. Hendrie, the Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1910 to 1922. Eight of these branchline locomotives were built and delivered by MLW in November 1918, numbered in the range from 1666 to 1673.
The locomotives were superheated, had Walschaerts valve gear and, like the Class MJ Mallets, had Belpaire fireboxes, but slightly larger boilers. When compared to the Class MJ, a distinguishing feature of the Class MJ1 was the sandbox, which was mounted on top of the boiler in North American style, to the rear of the steam dome. In general appearance, they bore a family resemblance to the Class 14C and Class 15B 4-8-2 locomotives, which were also built by MLW in 1918.
During 1922, the coupled wheels were retyred and their diameter was increased from 421⁄2 inches (1,080 millimetres) to 423⁄4 inches (1,086 millimetres).
The Class MJ1 was the last Mallet locomotive class to be placed in service by the SAR. All its subsequent new articulated locomotives were to be Modified Fairlies, Garratts and Union Garratts.
The Class MJ1 was also intended for branchline working and joined the Class MJ Mallets in service in the Eastern Cape. All eight were still in service by March 1948, but they were all withdrawn from service by 1960.
^ abcdeEspitalier, T.J.; Day, W.A.J. (1945). The Locomotive in South Africa - A Brief History of Railway Development. Chapter VII - South African Railways (Continued). South African Railways and Harbours Magazine, May 1945. p. 350.
^South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
^ abcdPaxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 88. ISBN0869772112.