The British Rail Class 50 is a class of diesel locomotives designed to haul express passenger trains at . Built by English Electric at the Vulcan Foundry in Newton-le-Willows between 1967 and 1968, the Class 50s were initially on a 10-year lease from English Electric Leasing, and were employed hauling express passenger trains on the, then non-electrified, section of the West Coast Main Line between Crewe and Scotland. Initially numbered D400–D449 and known as English Electric Type 4s, the locomotives were purchased outright by British Rail (BR) at the end of the lease and became Class 50 in the TOPS renumbering of 1973. The class gained the nickname "Hoovers" because of the noise made by the clean air plant at the No. 2 end, prior to refurbishment, which was likened to that of a vacuum cleaner, a name believed given to them by the staff at Paddington Station. Once the electrification from Crewe to Glasgow was completed the locomotives were moved to the Great Western Main Line (GWML) out of Paddington to allow the retirement of most of the remaining diesel-hydraulic locomotives then in use. As trains on the GWML steadily moved to High Speed Train operation from 1976, the Class 50s moved to hauling trains between London Waterloo and Exeter St Davids, and also trains from London Paddington to Hereford and Worcester via Oxford until the majority of those trains too were taken over by IC125 operation. The class was steadily retired from service in the late 1980s and early 1990s as their services moved to operation by second-generation Class 159 DMUs. Description Development The origins of the Class 50 lie in an invitation from the British Transport Commission (BTC) to manufacturers to produce a design for a lightweight Type 4 diesel locomotive with a gross power output of at least 2,500 hp. In order to produce a prototype quickly, English Electric based their design on that for their Deltic locomotives which were then in production. Unlike the Deltics, this design was powered by a single engine, the 16CSVT, a development of the 16SVT used in the Class 40 locomotives. Parts related to the contemporary Class 37s were also used. The result was DP2, a 2,700 hp Diesel-electric locomotive weighing 105 tons and with a top speed of 100 mph. However, before the prototype could be completed, English Electric's design was rejected by the BTC, primarily on the grounds