The New South Wales C36 class was a class of two-cylinder, simple, non-condensing, coal-fired superheated, 4-6-0 express passenger steam locomotives built by Eveleigh Railway Workshops and Clyde Engineering for the New South Wales Government Railways in Australia. Introduced in 1925, the 75 locomotives of the class became the principal motive power for all major expresses, and accelerated long-distance passenger timetables leading to new levels of service in the pre World War II period. They were the mainstay of passenger expresses for over 20 years before the advent of the 38 class. The class was used extensively for performance testing, and thus the development and trial of a number of technical improvements. Origins and development The 36 class was a relatively minor development of the 35 class locomotives, introduced in 1914. The first ten were built by the Eveleigh Railway Workshops, the remaining 65 by Clyde Engineering. The design was a response to the increased loading of express trains and public demand for shorter journey times, as well as to the need for reduced servicing and lower maintenance costs. Boiler All were superheated from the outset. The 36 class in original form had a round-top boiler rather than the Belpaire type. In the early to mid-1950s, the majority of the class were rebuilt with new, all-steel Belpaire boilers and re-designed cabs. Typical of the technology of the day, the riveted steel boilers originally fitted to the class had copper inner fireboxes, fire-tubes and superheater flues. The replacement Belpaire boilers had steel fireboxes, tubes and flues, in line with US practice and later NSWGR policy. Although copper provides superior heat transfer, it promotes a galvanic reaction resulting in the 'wasting' by corrosion of some steel boiler components such as crown stays and front tubeplates. Valve gear A noteworthy feature of the class was their outside Walschaerts valve gear, by then well-established in Britain and Australia and valued for its ease of lubrication and maintenance. The 36 class was the first mainline locomotive design in New South Wales to be so fitted, and all subsequent steam classes followed suit. In service Many of the old southern drivers claimed the 36 class were faster than the crack 38 class which arrived in later years, and were reputed to have reached speeds of over . The 36 class locomotives were placed on express passenger services, initially on the premier Newcastle Flyer trains, then later on