Charles Benjamin Collett’s Castle 4-6-0 is one of the most powerful and famous locomotive types ever produced by the Great Western Railway, writes Robin Jones.
Collett used Churchward’s Star class four-cylindered 4-6-0 of 1906 as the basis for the new design. It had the basic layout of the Star with an extended frame and a newly designed No. 8 boiler, which was larger, but equally importantly, lighter, to keep within the stipulated axle load limit. It retained the long-travel valves and Belpaire firebox that had become the trademark of GWR express locomotives. There was an increase in tractive effort to 31,625lb, and it was a locomotive that looked attractive and well proportioned.
The first of the initial ordered batch of 10 was No. 4073 Caerphilly Castle, which emerged from Swindon in the summer of 1923, and made its debut at Paddington on August 23 that year. It was the first of a series that remained in production right up to 1950.
Eventually 155 Castles were built new at Swindon; 15 were converted from Stars and Churchward’s one-off Pacific No. 111 The Great Bear became a Castle, Viscount Churchill. After a brief period of running-in service, between April and October 1924, Caerphilly Castle was exhibited at the British Empire Exhibition at Wembley Park alongside Nigel Gresley’s new LNER A1 Pacific No. 4472 Flying Scotsman, with the GWR claiming that the Castle was Britain’s most powerful express locomotive. To add substance to his bold claim, GWR general manager, Sir Felix Pole, proposed to the LNER that an exchange trial of the two types should take place. Accordingly, in April 1925, No. 4079 Pendennis Castle ran on the Great Northern main line and LNER A1 No. 4474 Victor Wild represented the LNER on the GW.
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