Oliver Bulleid’s Pacifics were perhaps the most controversial steam locomotives ever built in Britain. They seem to been loved and loathed in equal measure and the debate over their strengths and weaknesses took on a new dimension when BR decided to modify them in the 1950s. It was argued that they were too costly to operate and maintain, by comparison to other types available. Their time out of service, due to breakdowns, was also increasing to an unacceptable level, and some of Bulleid’s innovations were believed to be more hindrance than help. Rightly or wrongly BR were faced with a costly scrap and build programme or seek to make the engines more reliable. To Ron Jarvis, an engineer of note, fell the job of saving Bulleid’s enigmatic locomotives in a bid to satisfy the demands of the service. And he displayed a master’s touch in the programme that followed, saving the best of Bulleid’s work and adopting other established design principles. What emerged was described by Bert Spencer, Gresley’s talented assistant, as taking ‘a swan and creating a soaring eagle’. This book explores all the elements of the lives of these Pacifics and their two designers. It draws on previously unpublished material to describe their gradual evolution, which didn’t start or finish with the 1950s major rebuilding programme.