LMS 10000 / 10001

LMS 10000 and 10001 were the two prototype diesel-electric main-line locomotives designed by H. G. Ivatt and built at Derby Works in 1947–48, representing the London Midland and Scottish Railway's most ambitious venture into diesel traction and the first serious attempt to produce a main-line diesel locomotive capable of working the LMS's principal express services. The two locomotives established the template for British main-line diesel development that would eventually lead to the BR Type 4 locomotives of the 1960s, and their operation on the West Coast Main Line provided invaluable experience for what would become British Railways' modernisation programme.

Ivatt specified an English Electric 16SVT prime mover producing 1,600 hp — at the time the most powerful diesel engine fitted to a British railway locomotive — driving an electric transmission with four axle-hung traction motors in a 1Co-Co1 wheel arrangement. The Co-Co bogies gave six powered axles for adequate traction on the heavy Anglo-Scottish expresses, while the leading single axles on each bogie gave stability at express speeds. The locomotives were streamlined in a style influenced by American diesel practice and painted in LMS black with chrome trim, a striking modern appearance on a railway still overwhelmingly steam-worked.

Both locomotives passed to British Railways at nationalisation in 1948 and were occasionally paired together in multiple-unit on the West Coast expresses, demonstrating 3,200 hp on trains that had required two steam locomotives. After extensive BR service they were withdrawn in 1963–66. Neither was preserved despite their historic significance as the pioneering British main-line diesel prototypes. The National Railway Museum holds significant documentation on both locomotives.