|Total Number of Engines Built||21|
|First Engine Built||1911|
|Last Engine Built||1914|
|First Engine Written Off||1950|
|Last Engine Written Off||1960|
These were the largest non superheated six coupled engines to operate in the state. The class was introduced when it was proposed to increase the size of the Sydney Mail (via Wallangarra). They were originally used for this train and mail trains between Brisbane and Rockhampton. By 1930s, with the availability of superheated engines they were relegated to lesser duties. Four engines were attached to the Central Division during World War 2 and they worked as far north as Bowen. Upsurge of traffic during those hostilities caused them to again be pressed into heavy main line passenger work. In their final years they were restricted to slow goods and shunting trains. Like many saturated engines, they were heavy on coal and water. They were generally unpopular with crews particularly with poorer coals and heavy loads. Superheating was trialled on two engines, N°678 and N°610, in 1917 but proved unsuccessful, apparently due to problems lubricating the slide valves. Superheaters were removed when the engines were reboilered between 1929 and 1931. The class contained a number of unusual features. The safety valves were contained in a small dome mounted behind the large regulator dome. There was a large gap between the second and third sets of coupled wheels. One standard Sellers injector was fitted on the fireman’s side whilst the other was a Davies and Metcalfe combined injector and clack valve mounted on the boiler back plate. They were the first engines to be fitted with what became the standard QR whistle for the next 35 years. Scrapping of the class commenced in 1950 and the last two engines in service, N°689 and N°690, were written off in November 1960.