The Class 37, as it became, was an English Electric mixed traffic design, which entered service in 1960. It became the largest of all the Type 3 classes with 309 built. Construction took place between 1957 and 1962, but, over the following years, modifications and refurbishments created six subclasses, four of which have been modelled by Bachmann. Their original allocation was to the Western, Eastern and Scottish Regions but they were eventually to be found anywhere in mainland Britain.

In 1984, refurbishment was seen as an alternative to locomotive replacement, as it would give the British Railways Board more up to date machines within the budget available. 31 of the class underwent refurbishment at Crewe to become  the subclass 37/4 that were modified for passenger work by the addition of an electric train supply (ETS) for heating the carriages.