The South African Railways Class 20 2-10-2 of 1935 was a steam locomotive. In 1935, the South African Railways placed one Class 20 steam locomotive with a Santa Fe type wheel arrangement in service, designed and built at its Pretoria Mechanical Shops. In 1950, it was modified to an experimental condensing locomotive. The Class 20 was the third locomotive type to be designed and built in South Africa, after the Natal Government Railways 4-6-2TT Havelock of 1888 and the Class 2C of 1910. Construction The Class 20 2-10-2 Santa Fe type steam locomotive was designed in 1934 by A.G. Watson, Chief Mechanical Engineer of the South African Railways (SAR) from 1929 to 1936, and was built by the SAR at its Pretoria Mechanical Shops at Salvokop. The locomotive was intended for use on the South West Africa system, where the tracks consisted of section rail laid in desert conditions and practically without ballast. This restricted Watson to a maximum axle load of and he decided upon a Santa Fe type wheel arrangement with diameter coupled wheels and flangeless driving and intermediate coupled wheels. The sole Class 20 locomotive was numbered 2485. It was a hybrid, with a boiler which had been inherited from a Class 19A locomotive which had been equipped with a Watson Standard no. 1A boiler. The driving wheels were from scrapped Class 8 locomotives. The trailing pony truck was similar to that of the Class 19C, but the leading Bissel truck was specially designed. The bar frames and cylinders were imported. Even though it was not wholly a South African product with its imported frames and cylinders and its inherited boiler from a Swiss-built locomotive, this was the third recorded instance of steam locomotives designed and constructed in South African workshops after the Natal Government Railways' engine Havelock of 1888 and the Class 2C of 1910. Characteristics The cylinders, with rotary cam poppet valve gear, were identical to those of the Class 19C but with the stroke reduced from to . The modified cylinder covers had deep spigots to suit the reduction in stroke. The main drive and valve gear drive was from the third pair of coupled wheels. Grease lubrication was provided for all coupled wheel axle boxes. The ten-coupled wheel arrangement, in conjunction with the sharp curvature of the lines in South West, necessitated special side play for the leading coupled wheel axle boxes and