GWR Route: Banbury to Wolverhampton

Pre-grouping Locomotives at Leamington: gwrls248

GWR Atlantic 4-4-2 No 102 'La France' seen fitted with a later GWR boiler on an up express. This locomotive, built to a French design, was originally ordered by Churchward in order to compare the performance of this design to his own. A number of steam engine designs had applied the marine principle of re-using exhaust steam that still had considerable energy, in a second, lower-pressure set of cylinders. Churchward bought the De Glehn compound engine No 102 in 1903 and after having been tested in this configuration was subsequently rebuilt as a 4-6-0 (having been designed to accommodate this change). C1922

This engine had two high pressure cylinders between the frames, with pistons linked to the front driving wheels, and two lower pressure cylinders visible on the outside of the frames and wheels, set further back and acting on the second set of wheels; 4 cylinders in all. The French compound had a high boiler pressure when compared with its test rivals, and only when tested alongside 200lb/psi two cylinder engines without compounding (simple engines) was a valid comparison made.

Churchward found no efficiency advantage - but what he did find was that the smoother riding of the 4-cylinder engine encouraged economical use of steam by crews (who had tended to use long cut-offs to dampen rocking in two cylinder engines), and also gave huge scope for more power. The problems of loads on rods and axleboxes was also reduced by the French division of the drive across two sets of wheels. The concept of the GWR 4-cylinder engine was born.

The first of these new engine was No. 40, later named North Star, which emerged from Swindon works in 1906, in Atlantic 4-4-2 wheel configuration. It was as revolutionary to steam express locomotive building as Admiral Fisher's HMS Dreadnought was to battleship building in the same decade, and influenced all express steam engine designs in the UK after it.

The new engines of the 'Star' class, were all built with a 4-6-0 wheel arrangement, and No. 40, North Star was converted to this layout in 1909. 73 engines of this successful class were built, many lasting into the 1950s. One, Lode Star, remains as a static exhibit at the National railway Museum in York. The above courtesy of 6023 King Edward II Project.

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