South Australian Railways 500 class (steam)

ed 4-8-4 wheel arrangement in 1929, they remained in non-streamlined form throughout their service. Here no. 506 is on the 85-foot turntable in the roundhouse at Mile End locomotive depot, Adelaide The 500 class were part of larger order for 30 steam locomotives placed with Armstrong Whitworth, England, in 1924, as part of the rehabilitation of the state's rail system being overseen by Railways Commissioner William Webb. They replaced the Rx and S class locomotives, many dating back to 1894, that were still performing mainline duties, meaning that double and even triple heading was common. All ten 500-class locomotives arrived in Adelaide in 1926, and entered service on the Adelaide to Wolseley line as far as Tailem Bend. All were named after notable South Australians. ==Rebuilding==

In May 1928, 506 was experimentally fitted with a booster in a newly built four-wheel trailing truck, replacing the original unpowered two-wheel truck. The modification, popular in the United States, proved highly successful, increasing the locomotive's tractive effort from to . Boosters were subsequently fitted to the nine remaining locomotives, resulting in the class changing to 500B – although their popular name, among railway employees and the public alike, remained "Mountain class" rather than their new "Northern" configuration. With their upgraded tractive effort, the 500B class briefly became the most powerful non-articulated steam locomotives to operate in Australia until supplanted the following year by the New South Wales D57 class. Throughout the mid-1930s, all but two of the locomotives in the class were semi-streamlined and had valances fitted. The first two locomotives were withdrawn from service in 1955 and the last was withdrawn in 1963. ==Class list==