For as long as we could remember steam traction had been king on our railways. The resounding beat of exhaust from classic designs by Gresley, Stanier, Collett, Bulleid and many others had thrilled us all, while less prestigious ‘work-horses’ had kept commuters and freight moving throughout a vast network of major and minor routes. Mighty diesels had replaced them, notably the iconic Class 55 ‘Deltics’, setting new standards for speed and efficiency on the East Coast Main Line. Electrification became the ‘buzz-word’ as the need for speed increased and drove railway planning to a new level. The West Coast Main Line saw the wires go up by the mid-1970s and though other express routes would eventually follow the stage was set for the development and introduction of an alternative mode of traction for main lines not yet electrified, based on the concept of a powerful diesel locomotive at each end of a rake of newly designed carriages. The High Speed Diesel Train was thus conceived. Sleek and elegant. A modern design for a new age of rail travel. Capable of running at speeds of up to 125mph (201km/h) it was an immediate success and is still giving stalwart service some forty years later. A testament to its resilience. This is the story of the archetypal express diesel train – the Inter City 125.