BR Class 55

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The British Rail Class 55, also known as a Deltic, or English Electric Type 5, is a class of diesel locomotive built in 1961 and 1962 by English Electric for British Railways. Twenty-two locomotives were built, designed for the high-speed express passenger services on the East Coast Main Line (ECML) between Edinburgh and London King's Cross. They gained the name "Deltic" from the prototype locomotive, DP1 Deltic (the running number DP1 was never carried), which in turn was named after its Napier Deltic power units. At the time of their introduction into service in 1961, the Class 55s were the most powerful single-unit diesel locomotives in the world, with a power output of 3,300 hp (2,500 kW). They had an official service speed of 100 miles per hour (160 km/h), and introduced the first regular 100 mph diesel passenger service to Britain. They were capable of higher speeds than this, and often exceeded their official maximum in service, especially in their later years, with speeds of up to 117 miles per hour (188 km/h) being recorded on level gradients, and up to 125 miles per hour (201 km/h) whilst descending Stoke Bank. Despite their successes, the Deltics had a relatively short commercial service life of 20 years. From 1978, they were displaced by the next generation of high speed diesels, the "InterCity 125" High Speed Trains (HSTs). Deltics were subsequently relegated mostly to secondary services on the Kings Cross to York, Edinburgh and Hull routes, although they continued to operate some top-link trains, such as the Hull Executive, until 1981. As a small, non-standard fleet, with high running costs, no viable alternative use could be found for the Deltics, and all were withdrawn from service between January 1980 and December 1981. Six of the locomotives were saved for preservation.