The Kings were the final development of the Churchward four-cylinder 4-6-0, stretched to the very limits of the loading gauge. Many people have asked why this, the premier Great Western Railway express passenger class, had not been covered in the ‘Book of’ series when books had been devoted to the humble pannier tanks and the ‘lesser’ 4-6-0 classes. The answer lies partly in the mists of time - in the previous millennium when Irwell Press published Peto’s Register on the Kings in 1995. Although it has stood the test of time quite well, it was thought the material should be dusted down, refurbished and re-invigorated with a generous helping of new pictures to take its rightful place at the head of the GWR ‘Books of’. The Chairman of the Great Western wanted the most powerful express engines in the country, and the successors to the Castle were designed to achieve this. His publicity department, never shy of trumpeting the company to the outside world, took full advantage of its new engines and pressed its claim, both at home and to the world via a trip to the USA. They even produced a book titled The ‘King’ of Railway Locomotives and details taken from several of its chapters have been included as a fascinating contemporary account of the of the building of the engines. As befits their status, the Kings attracted much attention from the enthusiast community from first to last, and many column inches have been devoted to their workings in both contemporary and historical journals and magazines. In particular, the details of pre- and post-war diagrams compiled for the Great Western Railway Journal have been included in the chapter on operations.