They were built to assist conventional locomotives up and down a steeply graded rack railway section of the Central Western line at Mount Morgan. In 1906 a further pair were built by the North British Locomotive Company with a further two delivered in 1915. One of the original pair was condemned in 1926, with the remaining five withdrawn when the steeply graded section was bypassed in 1952. The only time the locomotives strayed from Mount Morgan was when sent to Rockhampton for overhaul.[1][2]