 By the time the contract for the J class had been awarded, the VR had already begun to receive deliveries of the B class mainline diesel-electric locomotives with VR unsuccessfully attempting to cancel the J class contract in favour of an order for branch line diesel locomotives.The J class was introduced for both passenger and goods traffic on Victoria's branch line network, with a maximum permissible speed of 45 mph (72 km/h), later raised to 50 mph (80 km/h).Dynamometer car tests showed the locomotive developed 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.