6th Class bar-framed locomotives in service, built by the North British Locomotive Company (NBL). They were experimental and were the first South African locomotives to have piston valves and superheaters. The pistons, with a diameter of , were the largest yet used on the 6th Class. The Schmidt superheater was of the smokebox type, but the arrangement was extremely complicated and not very successful. In 1912, they became the Class 6L on the SAR and in 1915, when they were reboilered, the superheaters were removed to convert them to saturated steam locomotives. At the same time the piston-valve cylinders were replaced with smaller slide-valve cylinders of bore. In 1897, the Pretoria-Pietersburg Railway in the Zuid-Afrikaansche Republiek (Transvaal Republic) purchased a tank locomotive with a wheel arrangement from the Lourenco Marques, Delagoa Bay and East Africa Railway in Mozambique. The locomotive was not classified, but named Portuguese and referred to by name. Narrow gauge In 1903, the CGR placed six Type B locomotives with eight-wheeled bogie tenders in service on the Avontuur narrow gauge line in the Langkloof. They were built by W. G. Bagnall and had bar frames, copper fireboxes and Stephenson valve gear. In 1912, they came into SAR stock and, in 1914, a further three locomotives with slightly longer boilers were acquired by the SAR. One of these was also built by Bagnall while the other two were built by Kerr, Stuart and Company. These three were commonly referred to as the Improved B. When a system of grouping narrow gauge locomotives into classes was eventually introduced somewhere between 1928 and 1930, they were to be classified as Class NG8 but had already been withdrawn from service. During 1915 and 1916, the SAR placed six locomotives in service in the Langkloof, built by Baldwin Locomotive Works. They were very similar to the Bagnall built Type B, except that they were equipped with Walschaerts valve gear. They were later designated Class NG9. Three of them survived in SAR service until April 1951, when they were sold to the Caminhos de Ferro de Moçâmedes (CFM) of Angola. (Also see Angola - Narrow gauge) Sudan During the Second World War, sixteen of the South African Railways (SAR) Classes 6 to 6D were transferred to the Middle East to assist with the war effort during the North African Campaign. The group consisted of seven Class 6, four Class 6A, two Class 6B,