English engineer Charles Benjamin Collett was born 10 September 1871. He was chief mechanical engineer of the Great Western Railway from 1922 to 1941 and designed (amongst others) the GWR’s 4-6-0 Castle and King Class express passenger locomotives. Collett’s predecessor, George Jackson Churchward had delivered to the GWR from Swindon a series of class leading and innovative locomotives, and arguably by the early 1920s the Great Western‘s 2-cylinder and 4-cylinder 4-6-0 designs were substantially superior to the locomotives of the other railway groupings.
In 1922 Churchward retired, and Charles Benjamin Collett inherited a legacy of excellent standardised designs. But, with costs rising and revenues falling, there was a need to rationalise the number of pre-grouping designs and to develop more powerful locomotives. Collett was a practical development engineer and he took Churchward’s designs and developed them – the Hall from the Saint class, and the Castle from the Star. He was also responsible for more humble locomotives, such as many of the pannier tank classes. He has received criticism by contemporary engineers and later railway historians for undertaking very little innovation in his designs, instead sticking with Churchward’s style in every case. Arguably this meant that by the time Collett retired the superiority of Great Western locomotives was lost to more modern designs, particularly those of William Stanier, who worked at Swindon before moving to the LMS in 1932, and took Churchward’s style with him but developed it in line with the progression in steam technology.
In 1926, something bigger than the Castle class was required to haul heavy expresses at an average speed of 60 mph. Great Western’s General Manager Sir Felix Pole told Collett to proceed with the design and construction of a “Super-Castle”. The result was the King class 4-6-0 design which emerged from Swindon works in June 1927. This had dimensions never previously seen, and represented the ultimate development of Churchward’s four cylinder concept. It was the heaviest (136 tons), and had the highest tractive effort (40,300 lbs.) of any 4-6-0 locomotive ever to run in the United Kingdom. Because of its weight, the King class was restricted to a limited number of the major GWR routes.