The BR modernisation plan of 1955 envisaged the replacement of steam traction with diesel and electric locos by around 1975. Chief among the requirements was a loco more powerful than the 2,000-hp locos that had been produced before then. The Sulzer Company in Switzerland were able to provide an engine of 2,300 hp, which was used in the Class 44. An updated 2,500-hp version was used in classes 45 and 46. There were 127 of these locos built at Crewe...