In 1921, the increase in holiday traffic from London to Devon and Cornwall was demanding heavier trains and the GWR management required a more powerful locomotive to haul them. The solution was to take the basic 4-6-0 layout of the existing Star Class and add a newly designed No.8 boiler, which was both larger and lighter. The result was the GWR Class 4073, or ‘Castle’ Class, which could both supplement the Stars and replace them on the heaviest expresses, including the Bristolian and the Cheltenham Flyer.
Between August 1923 and August 1950, 155 Castle Class locomotives were built new at Swindon Works, in ten lots for the GWR and two lots for British Railways’ Western Region, with a further sixteen converted from other classes. The fitting of double chimneys to selected engines, combined with larger superheaters, further enhanced their capacity for sustained high-speed performance, but by December 1965, the last of the class were withdrawn from traffic.
Locomotive No. 5050 Earl of St. Germans was built at Swindon in May 1936, originally being named Devizes Castle, and entered traffic at Worcester. Operating right across the GWR’s territory, from Laira to Shrewsbury, Earl of St. Germans was withdrawn from traffic on September 9, 1963, from St. Philip Marsh.