from the early 1900s to the 1920s the Great Western's 2-cylinder and 4-cylinder 4-6-0 designs were substantially superior to any class of locomotive of the other British railway companies. On one occasion, the GWR's directors confronted Churchward, and demanded to know why the London and North Western Railway were able to build three 4-6-0 locomotives for the price of two of Churchward's "Stars". Churchward allegedly gave a terse response: "Because one of mine could pull two of their bloody things backwards!" The biggest engineering challenge of the GWR's operations was travelling over the South Devon Banks, a series of steep inclines linking Exeter and Plymouth in Devon, on the GWR's most important route. Although speed was a key competitive driver across the whole GWR route, the South Devon Banks rewarded sure-footed locomotive designs with good adhesion. The largest opportunity to any GWR CME was the resulting large loading gauge legacy of the GWR's conversion from Brunel's broad gauge track to standard gauge, allowing for wider and higher designs than any of the other later Big Four railway companies. Philosophy Churchward's design philosophy followed a number of streams of development, for which he thoroughly researched both competitor UK designs, as well as European and North American locomotives. Following principles based on Belgian inventor Alfred Belpaire, Churchward preferred free steaming boilers. This resulted in his use of a Belpaire-style rectangular firebox, which due to its greater surface area for evaporation was less prone to foaming and carry over of water to the cylinders. Churchward inherited from Dean a series of parallel cylindrical boilers, but by applying mathematical principles to the flow of boiler water, quickly improved the flow of steam by adopting tapered boilers, which give their largest area to the point of highest steam production. Churchward then dispensed with the need for a large dome to collect steam, using instead top-feed of water supply from injectors, which together with top-fitted clack boxes hidden within a brass "bonnet" minimised boiler stress. Churchward experimented with compounding, a principle development for marine engines which was widely adopted in European locomotive design. Although through his experimentation Churchward found little difference in operation in terms of the total power developed in compounding locomotives, the use of European locomotives in his trial led to his adoption of higher pressure boilers, and drive power split between two axles on four cylinder designs. His third stream of philosophy was