Without doubt the most successful diesel design of the BR era and a strong contender to be called the greatest locomotive in British railway history, the definitive model of the English Electric Type 3 / Class 37 has been a long time coming. 309 examples of this mixed-traffic 1,750hp Co-Co class were built by English Electric and Robert Stephenson & Hawthorn between 1960 and 1965 to two basic designs, split and centre headcode. They could be found systemwide leading all kinds of freight and passenger services. 135 were rebuilt in the mid 1980s giving the class a further lease of life, while further major rebuilds have taken place since privatisation. Many are still hard at work today painted in the colours of a wide range of different operators including Network Rail and a plethora of private freight and passenger companies, such as Colas Rail, Direct Rail Services, Europhoenix, HN Rail and WCRC.