Originally the DD Class, 94 D1 or D2 class locomotives were converted between 1929 and 1947 into the 4-6-0 D3 class. The D3 class, with its relatively low axle load, and efficient coal usage, delivered superior performance to most branchlines across the Victorian Railways network. Many D3 classes stayed in service for a half-century, with the last retired in 1974, despite originally being constructed from 1902. This publication covers their stay in service from the late 1940s until they were retired from service. D3 639, remains in operational preservation with Steamrail today.