 Bulleid proposed an initial design based on his SR Q1 class locomotive, which had proved easy to maintain in service.As the proposal progressed, Bulleid saw that certain tasks required with conventional steam locomotives could be eliminated by adopting some of the features of the contemporary Southern electric locomotives.However, one of the subsequent designs of a 0-4-4-0 wheel arrangement had an unacceptably high axle-loading of , which increased the risk of damaging the Southern Railway's track.