The British Rail Class 37 is a diesel-electric locomotive. Also known as the English Electric Type 3, the class was ordered as part of the British Rail modernisation plan.
They were numbered in two series, D6600–D6608 and D6700–D6999.The Class 37 became a familiar sight on many parts of the British Rail network, in particular forming the main motive power for InterCity services in East Anglia and within Scotland. All locomotives would be renumbered from 1973 under the TOPS renumbering system, sometimes multiple times as the exact specification for single locomotives could be changed.
They performed well on secondary and inter-regional services for many years. The Class 37s are known to some railway enthusiasts as 'tractors', a nickname due to the agricultural sound of the diesel engine of the locomotive. A total of 309 of the class would be built with 35 preserved and 66 still in service as of 2023.