The C17 class was introduced as an improved version of the C16 class. Per Queensland Railway's classification system they were designated the C16 class, C representing they had four driving axles, and 17 representing the cylinderdiameter in inches. The design was so successful that 227 locomotives were built from 1920 when the first engine Nº 15 entering service through until 1953 when Nº 1000 was delivered. The Commonwealth Railways NM class were of the same design. They were used to haul Mail trains on lines could not accommodate heavier B18¼ class, also suburban passenger, mixed, goods and branch line trains. Until 1948 they were the heaviest engines that could work north of Mackay. Prior to the introduction of diesel electric locomotives, they were responsible for hauling the air-conditioned Inlander, Midlander and Westlander trains for parts of their respective journeys. First engines had large steam domes, open cabs and C16 style tenders. Those built from 1938 onwards, commencing with N°858, had small steam domes, sedan cabs with welded tenders and also larger diameter piston valves. The two types of boilers were occasionally interchanged at overhauls and by later years most of the old style ones had been replaced. The last 40 engines, Nº961 to Nº1000, were fitted with Timkenroller bearings and painted brown. They acquired the nickname of Brown Bombers after American boxerJoe Louis. Those overhauled in the last years of steam operations were repainted black. A number of modifications were carried out over their life including the fitting of large mushroom air snifting valves. Several had additional sandboxes and/or rear headlights fitted at various times for working lines where no turning facilities were available. On 5 May 1947, C17 class locomotive 824 left the rails near Camp Mountain on the Dayboro line claiming the lives of 16 people and 38 injured. The Commonwealth Department of Trade & Customs Recreation and Social Club had chartered the train for a picnic at Closeburn. Negotiating a sharp curve at excessive speed caused the tragedy. The locomotive was repaired and continued in service until May 1967 when it was transferred to Injune along the recently closed line.
