|Total Number of Engines Built||83|
|First Engine Built||1926|
|Last Engine Built||1947|
|First Engine Written Off||1967|
|Last Engine Written Off||1970|
The engines were designed to haul Mail Trains and were the principal engines used on these services until the introduction of the BB18¼ and diesels. Nevertheless, they spent much of their working lives on goods trains and suburban passenger workings. They were generally popular with crews and had free-steaming boilers.
A prototype engine, N°84, was constructed by Ipswich Workshops and ran to Grandchester on 16th July 1926. After successful trails on both the Sydney and Townsville Mail Trains, approval was granted in 1927 to construct a further eight engines at Ipswich and another eight were ordered in 1929. A proposal to fit a Franklin booster to the trailing truck was rejected. These first seventeen engines were constructed with open cabs and C16 style tenders. Six engines built in 1935 were the first to be fitted with sedan cabs but retained old style tenders. Commencing with N°841 in 1936, all engines were built to what was considered the “standard” B18¼ design with sedan cabs, new style tenders and larger 9½” diameter piston valves.
A number of modifications were carried out during their lives. The 1935 engines were fitted with MeLeSco multiple valve regulators mounted on the superheater header. These were later replaced with standard regulators in the boiler dome. N° 843 was fitted with an ACFI feed water heater when it entered service in 1936 but had it removed in 1942. Early engines were fitted with Alligator crossheads. The Laird type was used on those constructed at Ipswich in 1939 commencing with N°870. Minor changes were made to boilers over the years. A few engines acquired BB18¼ boilers during overhaul and later a “standard” boiler was designed for use by both classes. All B18¼ chimneys were cast with capuchions, but several were later ground off due damage in service.
All members of the class were painted green commencing with N°50 & N°911 in 1949; however, several engines that were overhauled in the final years were repainted black. N°895 was the first of the class to have its headlight moved to a bracket in the centre of the smokebox door. Most other members of the class were similarly altered.
The last two engines in service were N°770 at Mackay and N°842 at Ipswich.
N°84 attained the highest mileage of any QR steam engine, travelling 1,472,859 miles during its life of 42¼ years.
~ Some tenders types were exchanged during service
* Engines constructed since 1936 (N°841 onwards)
** Engines constructed since 1939
# Some WH pumps later changed when engines underwent boiler exchanges.
Ipswich – Ipswich Railway Workshops
Walkers – Walkers Ltd, Engineers, Maryborough