The 48-Class, The Backbone of the Railways. In the mid 1950s, the New South Wales railways were suffering cost pressures due to the ageing and inefficient steam locomotive fleet. This was particularly so in country areas where steam locomotives were poorly suited to the longer distances between servicing points on the multitude of branch lines. The successful introduction of diesel-electric locomotives into main line work during the 1950s, led to the view that the answer for branch lines might lie with this new form of motive power because of its greater operating range.