 To keep the axle load to 19.5 tons, the design by 1944 had changed from a 4-6-2 'Pacific' to a 4-6-4 'Hudson' wheel arrangement.The R class reflected an ongoing evolution of VR locomotive design and a response to the changing operational environment of the VR in the postwar era.The R class adopted the bar frame construction of the H and S class express passenger locomotives, which had proven to be far more robust in coping with the VR's varying track quality than the fracture-prone plate frames of the A2.