Built at Crewe Works in 1973 – 75 for the extension of the 25kV overhead wiring to Glasgow, these locomotives have been the mainstay of this demanding route until the arrival of the “Pendolino” trains. The locomotives feature four GEC G412AZ frame mounted traction motors, delivering a continuous rating of 3730 kW, (5,000 hp). TDM multiple working is provided, enabling push-pull operation with driving van trailers and coaching stock using the standard RCH jumper. The locomotives are a development from Class 86 locomotives and use camshaft control, avoiding the complications of electronic drives. Their high power rating enables their use on all types of train from express passenger to freight.