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 rest is history!