[1] During the early 1950s, the Victorian Railways (VR) 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 underinvestment during the Great Depression, and the heavy workload imposed by World War II.

[2] Victoria's branch line railway network, laid with 60 lb/yd (29.8 kg/m) 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, were at the end of their life.

However, the extra length of those locomotives (being a total 67 ft or 20.42 m long) made them unsuitable for a number of branch lines where only a 50-or-53-foot (15.24 or 16.15 m) turntable was available.

Dynamometer car tests showed the locomotive developed 930 hp (694 kW) at the drawbar at around 20–25 mph (32–40 km/h), which suited the relatively low speed limits of much of the Victorian branch line network.

Following recommendations from the 1957 Australian and New Zealand Railway Conference, locomotive J546 was selected for the installation of a Laidlaw-Drew oil firing system in place of the convention weir-type burner.

However, the locomotive was found to steam poorly under load using the Laidlaw-Drew system and was converted back to weir burner operation.

[11] By the late 1960s, the J class was largely relegated to shunting at various country yards, with many losing their cowcatchers and gaining shunter's steps on sides of the tender.

[18] J550 holds the distinction of being the very last steam locomotive in normal revenue service on the Victorian Railways, being rostered on the 6 a.m. Bendigo pilot on 25 May 1972.