spherical bearings for the leading crank pins. The design of the leading Bissel truck necessitated certain proportions to suit the ten-coupled wheel arrangement, but the trailing Bissel truck was similar to that of the Class 19C. Its axle boxes were provided with end thrust pad bearings attached to the axle box covers, which relieved the ends of the bearing from the effects of end thrust. This device proved successful in reducing the number of hot boxes on trailing Bissels. The locomotive was tended by a Type MP1 tender with a coal capacity, a water capacity and a axle load. The total weight of the engine and tender in full working order was . Watson disliked articulated locomotives and his aim with the Class 20 was to build an as powerful as possible non-articulated locomotive with a maximum axle load. The resulting Class 20 could be considered as Watson's answer to the Class GCA Garratt locomotive which had very similar weight and tractive effort capacities. The Class 20 carried more water and coal than the Garratt and was about heavier with tractive effort compared to the of the Class GCA. Even so, only one Class 20 was produced and the design was not repeated. The construction of this sole Class 20 locomotive marked the beginning of a research process which was continued two years later with the construction of the sole Class 21 2-10-4 and which eventually culminated in the procurement of the Class 23 4-8-2 fleet in 1939. Service The locomotive was intended for goods traffic on light rail in South West Africa, even though freight traffic volumes in that territory were hardly enough to justify such a powerful engine. It was sent to various branches in the Eastern Transvaal to undergo tests before it entered service in South West Africa, but after some evidence that the engine was rather severe on the light track, it was returned to South Africa after comparatively short service. It was then allocated to Pretoria for working on the Eastern Transvaal System where its power capacity could be used more productively. Photographs show that, after being returned to Pretoria, the engine's Type MP1 tender was replaced by a larger Type MT2 tender with a coal capacity, a water capacity and a axle load. The total weight of the engine and Type MT2 tender in full working order was . The Pretoria enginemen considered the