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. The Class 37 became a familiar sight on many parts of the British Rail network, in particular forming the main motive power for Inter-City services in East Anglia and within Scotland. They also 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. As part of the large scale dieselisation brought about by the British Rail modernisation plan a need was identified for a number of type 3 locomotives of power output 1,500 hp (1,100 kW) to 1,999 hp (1,491 kW). English Electric had already been successful with orders for type 1 and type 4 diesels, and had produced locomotives of similar power to that which was required for railways in East Africa. A design based on the exported locomotives was put forward and accepted. The design was for a general purpose locomotive and initially found service in British Rail's Eastern Region. There was no prototype.