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English: Victoria Railways 5'3" gauge A H Ahlston 'R' Class 4-6-4 No.R704, built by North British (No.26994) in 1950 at the Victoria Railway Museum, North Williamstown, 2 April 2016. No.R704 has polished steel boiler bands because it was displayed at the 1951 Festival of Britain. 70 'R' Class were built by North British in 1950-53 and they were withdrawn in 1960-74. They had 6' 1" SCOA-P driving wheels, SKF roller bearings on all loco and tender axles, bar frames,mechanical stoker for the firebox (with a 42 sq. ft. grate), 210 psi boiler pressure, two 21.5" x 28" cylinders, 2,705 sq ft total heating surface, a tractive effort of 32,080 lbs and weighed 107t 12c (engine only). They had a designed output of 1,840 dbhp. The design process for the 'R's' started in the 1920's as a Light Pacific for the main lines which could not accommodate the high axle load of the Heavy Pacific of the 'S' Class. However, a protracted design process and then delay caused by the war resulted in the design being updated in the late 1940's: the replacement of plate frames by bar frames, an increase in firebox size and grate area, the addition of a mechanical stoker and the facility for them to be converted to standard gauge which all increased the weight and axle load so that a 4-wheeled trailing truck had to replace the 2-wheeled type, resulting in a 4-6-4. 1 was fitted with Stug brown coal apparatus from 1954-57 and 2 were fitted for oil burning in 1956-57 but plans to retro fit all the class for oil firing was abandoned. Unfortunately, theyowere delivered on the eve pf dieselisation and they were displaced from the top expresses quickly. They did not have a long life.