In the fifties, British Railways searched for a way to replace the fastest steam-hauled express services on the East Coast Main Line between King's Cross and Edinburgh. Since electrification of the complete ECML was not foreseeable in the near future, this had to be a diesel locomotive that could reach a higher average speed than the streamlined A4 Pacific. The answer was the DP1 prototype completed by English Electric in 1955. It was the most powerful single-unit diesel locomotive in the world at the time of its introduction into service.