The versatile and reliable Class 37s quickly established themselves as a firm favourite with engine men and enthusiasts alike. Equally at home in charge of Class 1 passenger or heavy freight trains they would prove their worth over lines the length and breadth of the network, operating from their initial delivery in 1960 through the demise of steam traction and even into the modern era. This book explains their origin, development and operation, with information on every one of the 309 examples introduced. Over time numerous modifications were made resulting in a number of sub-classes. Many are described in detail, including black and white and colour photographs depicting their transformations through the decades. Soon becoming the traction of choice to head rail-tours they were, and still are, in great demand by the preservation movement. They continue to attract enthusiasts of classic traction and several are key members of the locomotive pools of heritage railways throughout the land. David Mather describes the long and successful career of this iconic class and explains the origin and demise of those which succumbed to the cutter’s torch, together with details and up to date photographs of many in preservation, where they continue to operate to the delight of railway enthusiasts of all ages.