In 1929 and 1930, the South African Railways placed eight Class GL Garratt articulated steam locomotives with a 4-8-2+2-8-4 Double Mountain type wheel arrangement in service.

Built by Beyer, Peacock & Company in Manchester, England, they were originally designed to work on the Durban to Cato Ridge section of the Natal mainline.

The Class GL was eventually displaced to the route between Glencoe and Vryheid before spending their final working years operating on the line from Stanger to Empangeni.

[1][2][3][4][5] The Class GL had its origin in the steady increase in loads experienced by the Natal mainline in the years prior to the First World War.

[1][2][6] The decision to electrify the line from Glencoe Junction to Durban had been taken in 1914, coincidentally the year in which the South African Railways (SAR) ordered its first Cape gauge Garratt, the Class GA 2-6-0+0-6-2.

[6] Despite this delay, the process of electrification began in earnest in 1922 and by 1926 full electrified haulage had been instituted between Glencoe and Pietermaritzburg, with lashups of three electric locomotives being used on the heaviest freights.

Collins DSO, the Chief Mechanical Engineer (CME) of the SAR from 1922 to 1929, prepared the specifications and the contract for the design and construction of these locomotives, the Class GL, was awarded to Beyer, Peacock & Company.

[1][2][6] This suggested that the Class GL had still more to give, which was confirmed on the following day's testing when a load of 1,205 long tons (1,224 tonnes) was hauled over the same stretch of track.

Apart from demonstrating the Class GL's power and capacity for hauling heavy trains, these tests also showed that their running qualities were exceptional, being smooth and free-running machines.

[6] The Class GL made use of Beyer, Peacock's standard lever-actuated Sterling-type steam-operated power reverser and a Pyle National Company turbo-generator.

The cylinders, of the same bore and stroke as those of the Class 14, drove the third coupled axles using long connecting rods which stabilised the locomotive by reducing vertical forces at the crosshead to a minimum.

[2][3][6] To allow for the tight curves, including 300 feet (91 metres) radius bends with 4+1⁄2 inches (114 millimetres) superelevation without any intermediate tangent and the steep, twisting nature of the line, the front engine unit's pivot bearing was spherical, with its alignment controlled by sprung rollers.

Beyer, Peacock estimated the Class GL locomotive's economical coal consumption rate at 3+1⁄2 long tons (3.6 tonnes) per hour.

[1][2][6] The Class GL had a rocking grate and self-cleaning hopper ashpan with water and steam sprayers to dampen down the ash to prevent it from entering axle boxes, motion areas and other friction-sensitive places.

Since Garratts are designed to be bi-directional, the problem was eventually solved by simply running them with the chimney trailing on the ascending legs of the tunneled routes.

Though briefly considered as hump shunters at Bloemfontein, the Class GL had outlasted its use and after some forty-two years of working the most difficult terrain on the SAR, they were withdrawn from service in 1972.