The South Australian Railways W and Wx class was a class of 2-6-0 steam locomotives operated by the South Australian Railways. Some were used by the Commonwealth Railways in the Northern Territory and by contractors. History The W class was the second class of locomotive built to the 2-6-0 (Mogul) wheel arrangement to be supplied to the South Australian Railways (SAR) – the first being the U class, of which there were only eight. The class eventually totalled 35 in number and saw service on every SAR narrow gauge line. The locomotives were first introduced in 1878 during a period of rapid expansion of the railway system. The class were ordered as light goods locomotives for use on the expanding South Australian Railways gauge lines, necessarily limited in size and weight by the lightweight 40 lb/yd rails used at the time. The locomotives were built by Beyer, Peacock & Co. of Manchester. Early W class units were used during construction of the Central Australia Railway between Port Augusta and Quorn in 1878 before entering revenue service with SAR. During their operational career, the locomotives were used within South Australia on the isolated Eyre Peninsula Railway, in the south east on now closed lines in the Kingston, Naracoorte and Mount Gambier areas as well as the line north from Port Augusta. Many were sold or leased to contractors and they were also used by the Railways Construction Branch. Several of the locomotives were sold to C&E Millar and used for construction of the Palmerston and Pine Creek Railway in the Northern Territory and would continue to work the isolated line for the remainder of their operational lives. Wx and NF classes From 1903, the SAR began to rebuild W class locomotives with upgraded boilers increased to pressure, which improved the tractive effort to . 18 of the class were rebuilt and designated Wx class. In 1911, administrative responsibility for the Northern Territory, including the Palmerston and Pine Creek Railway, was passed from South Australia to the Commonwealth. Five unmodified W class locomotives were transferred to Commonwealth Railways at the Parap railway workshops and designated NF class. The condition of these locomotives was such that W35 and W41 were stripped down and the parts from both used to make NF7 an operational locomotive. Commonwealth Railways purchased an additional two locomotives of the class in 1915 from private interests involved with building the