As a development of the C16, C.F. Pemberton developed the class C17. While the letter C stood for four coupled axles, the 17 indicated the cylinder diameter in inches. Production took place on a large scale in QR's own workshops and at other manufacturers, and the Commonwealth Railways also ordered 22 identical units as the NM class.
The locomotives initially had open cabs, large steam domes and a Robinson type superheater. The engines that were completed after 1938 had closed cabs, smaller domes, new tenders and larger slide valves. The last 40 examples used Timken roller bearings, which in connection with the brown color scheme led to the nickname “Brown Bombers”, after the boxer Joe Louis.
The C17 quickly gained a reputation as a versatile and powerful locomotive. It was used with all train types from passenger over suburban to freight trains. Thanks to the low axle load, they could also be used in front of mail trains where the axle load of the Pacific class B18¼ was too high. The production of a total of 227 units ran over a long period from 1920 to 1953. Just one year after the end of production, the older engines were taken out of service, and the last survived into the late 1960s.