The single largest class of new locomotive to be constructed after the nationalisation of Britains railways in 1948, the 251 representatives of the Riddles-designed Class 9F 2-10-0, were amongst the most powerful steam locomotives ever constructed in the United Kingdom. First introduced in 1954, these impressive locomotives were destined never to fulfil their true potential as, in 1955, the Modernisation Plan foreshadowed the complete elimination of steam traction from Britains railways. Construction of the class continued until 1960, when No 92220 Evening Star became the last main line steam locomotive to be constructed for use by BR. By this date, however, it was clear that the class was destined to have a relatively short life and, by the end of main line steam in August 1968, most of the class had already been withdrawn, many after less than a decade in service. Though designed primarily for heavy freight traffic, they performed superbly on services such as the iron trains from Tyne Dock to Consett, the 9Fs were equally at home on passenger turns. Amongst the routes that saw the class regularly hauling passenger trains was the Somerset & Dorset line between Bournemouth and Bath. In his latest contribution to our now well-established Locomotives in Detail series, David Clarke examines the development, history and operational career of the 9Fs. With a superb selection of both colour and mono illustrations, line drawings and a detailed narrative, the author explores how, despite its relatively short career, the class was to see significant modification. Apart from the ill-fated experiment to construct 10 members of the class with Franco-Crosti boilers, there were also considerable variations in terms of the tenders utilised and the liveries carried. Though perhaps representing the ultimate in BR steam locomotive design, the tragedy was that the 9F class emerged too late to affect the course of traction history. By the time that they were built, steam was already being consigned to the history books. The 9F, however, remains a pivotal and popular design and this addition to the successful Locomotives in Detail series is certain to be required reading for all those interested in the development of BR main line steam after Nationalisation and all those involved either in preservation or railway modelling the period between 1954 and 1960.