 Introduced almost concurrently with the diesel-electric locomotives that ultimately superseded them, these locomotives were only in service for a relatively short time.During the early 1950s, Victorian Railways embarked on a massive upgrading of its ageing locomotive fleet as part of 'Operation Phoenix', an £80 million program to rebuild a network badly run down by years of Depression-era underinvestment and wartime overutilisation.Victoria's branch line railway network, laid with rail and featuring gradients of up to 1 in 30 (3.33%), was still largely served by the D1, D2 and D3 variants of the once 261-strong 1902-era Dd class 4-6-0, which by the early 1950s was at the end of its life.