The Class 37 was ordered as part of the British Rail Modernisation Programme which began in the early 1960s. Introduced between 1962 and 1966, the Class has been able to reach all corners of the UK railway network over the following 45 years.

Construction of the 309 machines was split between English Electric's Vulcan Foundry in Newton-le-Willows, and Robert Stephenson & Hawthorns' of Darlington. The machines initially were numbered D6700-D6999 and D6600-6608 respectively.

They became the mainstay of locomotive power for InterCity services in East Anglia and around Scotland, while also working secondary and inter-regional routes for many years.

Designed for both freight and passenger services, the class was as much at home hauling a heavy goods train as it was pulling passenger coaches. The Western Region even made attempts to convert several examples for 100Mph operations.

Type 3 locomotives were originally fitted with boilers for steam heating, but with the withdrawal of non-standard Type 2 and 3 locomotives these were removed.

Heavy overhauls of the class took place throughout the 1980s with the intention of prolonging the life of many examples well into the 1990s and beyond. At this point the refurbished Class 37/4 was introduced. They were rewired, had CP7 bogies installed with a slower top speed of 80Mph and a Brush alternator and electric train supply (ETS) fitted.