The 49 class were originally purchased to dieselise the (then) uneconomical line to Broken Hill. Initially, the entire class would be based at Parkes, although their duties would take them all over Western NSW, hauling anything from a block wheat train, to a pickup goods, and even the Central West Express on occasion. Originally, six 875hp units were ordered from Clyde Engineering, with a Co-Co wheel arrangement – giving them an axle load of 12.5 tons. These units were very similar to the T Class purchased by the Victorian Railways, having entered service four years prior. A further twelve units would be ordered, in two batches of six units each.