Ordered from the Vulcan Foundry 12 were placed in service in 1887. They had the 4-4-0 wheel arrangement that most locomotives had at the time. Shortly after delivery the class leader was tested against the Baldwin Locomotive Works built L304 class to see which one could make a faster and better run across the Blue Mountains to Eskbank,with the Baldwin locomotive judged superior. They were also intended to haul passenger service on the steeply graded Sydney to Newcastle and Kiama lines.
They proved unpopular with both locomotive crews because of rough riding and track maintenance staff because of their high axle load and were displaced from mainline working and relegated to branch line work following the arrival of the P6 class. In 1905/06, new boilers with Belpaire fireboxes were fitted, the smokeboxes shortened and the cylinder diameter reduced. In 1924 the class was renumbered becoming the Z17 class.