English Electric DP1, commonly known as Deltic, was a prototype 3,300 hp (2,500 kW) demonstrator locomotive employing two Napier Deltic engines, built by English Electric in 1955. The high power of the locomotive at an acceptably low axleload resulted in 22 similar locomotives being ordered by British Railways for use on East Coast Main Line express passenger services; the serial production of which became the British Rail Class 55.