The British Rail Class 40 is a type of British railway diesel electric locomotive. A total of 200 were built by English Electric between 1958 and 1962. They were numbered D200-D399. They were, for a time, the pride of British Rail's early diesel fleet. However, despite their initial success, by the time the last examples were entering service they were already being replaced on some top-level duties by more powerful locomotives. As they were slowly relegated from express passenger uses, the type found work on secondary passenger and freight services where they worked for many years. The final locomotives ended regular service in 1985. The locomotives were commonly known as "Whistlers" because of the distinctive noise made by their turbochargers. Origins The origins of the Class 40 fleet lay in the prototype diesel locomotives (LMS No. 10000 and 10001 ordered by the London, Midland and Scottish Railway and British Railways and D16/2 ordered by British Railways between 1947 and 1954) and most notably with the Southern Region locomotive No. 10203, which was powered by English Electric's 16SVT MkII engine developing 2,000 bhp (1,460 kW). The bogie design and power train of 10203 was used almost unchanged on the first ten production Class 40s. Prototypes British Railways originally ordered ten Class 40s, then known as "English Electric Type 4s", as evaluation prototypes. They were built at the Vulcan Foundry in Newton-le-Willows, Lancashire. The first locomotive, D200, was delivered to Stratford on 14 March 1958. Following fitter and crew training, D200 made its passenger début on an express train from London Liverpool Street to on 18 April 1958. Five of the prototypes, Nos. D200, D202-D205, were trialled on similar services on the former Great Eastern routes, whilst the remaining five, Nos. D201, D206-D209, worked on Great Northern services on the East Coast Main Line. Sir Brian Robertson, then chairman of the British Transport Commission, was less than impressed, believing that the locomotives lacked the power to maintain heavy trains at high speed and were too expensive to run in multiple – opinions that were later proved to be correct. Airing his views at the regional boards prompted others to break cover and it was agreed that later orders would be uprated to 2,500 hp (a change that was never applied). Direct comparisons on the Great Eastern Main Line showed they offered little advantage over the "Britannia" class steam locomotives when driven well,