The South African Railways Class NG1 0-4-0T of 1900 was a narrow-gauge steam locomotive from the pre-Union era in Transvaal. In 1900, the British War Office placed two Sirdar class narrow-gauge steam locomotives in service near Germiston. At the end of the Second Boer War, the locomotives were sold to a farmer who used them on a firewood line out of Pienaarsrivier, until the line and locomotives were taken over by the Central South African Railways. In 1912, when these locomotives were assimilated into the South African Railways, they were renumbered with an "NG" prefix to their numbers. When a system of grouping narrow-gauge locomotives into classes was eventually introduced somewhere between 1928 and 1930, they were designated . Manufacturer Three Sirdar class narrow-gauge steam locomotives were built for Allan Alderson and Company of Cairo, for use during the Nile Barrage construction in Egypt. In November 1899, the Director of Army Contracts of the British War Office ordered two narrow-gauge steam locomotives from Kerr, Stuart and Company for delivery within ten days, since the locomotives were urgently needed by the Royal Engineers for use in a siege park in the Zuid-Afrikaansche Republiek where the Second Boer War was in progress. A siege park was a depot for holding engineer’s stores which could be required during a siege. By diverting two of the three locomotives which were ready to be shipped out to the Nile Barrage construction works in Egypt, the locomotive builders were actually able to supply the engines within four days. The standard Sirdar class engines were similar to the single gauge engine Hope which had entered service in Walvis Bay in 1899, but without the leading and trailing pony wheels. Kerr, Stuart was a supplier of contractor's engines and often built locomotives to standard designs, but without frame stretchers and axles, and kept them in stock until an order was placed. This allowed them to be delivered with a minimum of delay. The 600 and 610 millimetre gauges The locomotives had plate frames and used Stephenson valve gear. Although they were eventually classified as narrow-gauge locomotives along with the rest of the South African narrow-gauge locomotive fleet, they were actually constructed to the metric gauge. Historically, the actual two feet narrow-gauge rail spacing depended on whether or not the track was laid by a metricised country. German-built narrow-gauge lines in Deutsch-Südwest-Afrika (DSWA) were therefore gauge, while those in