The design was based on the earlier Stanier LMS Stanier 2-6-4T, which was derived from Henry Fowler's LMS Fowler 2-6-4T engine. Fairburn modified the design to have a shorter wheelbase, reduced from 16 ft 6 in (5.03 m) to 15 ft 4 in (4.67 m) allowing curves of 5 chains to be negotiated; to reduce the locomotives mass per unit length the overall weight was reduced by 3 long tons 8 cwt (7,600 lb or 3.5 t). It was also the basis for the later British Rail Standard Class 4 tank.