Per Queensland Railway's classification system they were designated the PB15 class engine, P representing they were a passenger locomotive, the B that they had three driving axles and the 15 the cylinder diameter in inches.

By 1912, a total of 202 engines had been built by Walkers (122), Evans, Anderson, Phelan & Co (70), Kitson & Co (20) and Toowoomba Foundry (20).

[2][4] In 1924 one example of the engine was built by North Ipswich Railway Workshops for the Aramac Shire Tramway.

These engines of these wheel arrangement were fitted with larger tenders and Walschaerts valve gear.

[2][4] In 1932, a number of PB15 class locomotives attached to Ipswich depot were fitted with a second sandbox for rear sanding to assist with shunting work on the colliery branches.