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 locomotives were commonly known as "Whistlers" because of the distinctive noise made by their turbochargers. The final locomotives ended regular service in 1985, although several examples are preserved.