the british rail class 55 is a class of diesel locomotive built between 1961 and 1962 by english electric. they were designed for the high-speed express passenger services on the east coast main line between london king's cross and edinburgh. they gained the name "deltic" from the prototype locomotive, dp1 "deltic", which in turn was named for its napier deltic power units. 22 locomotives were built, and they dominated services on the line until their withdrawal at the end of 1981. six locomotives were preserved and are still running today.