The British Rail Class 15 diesel locomotives, also known as the BTH Type 1, were designed by British Thomson-Houston, and built by the Yorkshire Engine Company and the Clayton Equipment Company, between 1957 and 1961. They were numbered D8200-D8243.

The Class 15 was ordered by British Railways (BR) shortly after the announcement of the 1955 Modernisation Plan, which led to the procurement of a diverse number of diesel locomotives under the 'pilot scheme'. Shortly following the completion of the first locomotive during 1957, its performance was sufficient to justify multiple follow-on orders, leading to a total fleet of 44 locomotives. In service, the type was relatively unreliable, much of this been traceable to its Paxman 16YHXL power unit. Its fortunes were further impacted by inconsistent policy making.

During the late 1960s, it was decided to withdraw the Class 15 in favour of the more numerous and successful British Rail Class 20 locomotive, both types having been developed to satisfy the same Type 1 specification. Their final use was as departmental vehicles, coming to an end in the late 1980s. One example has survived into preservation.