The British Rail Mark 3 Coach is a type of passenger carriage developed primarily for the High Speed Train (HST) in an effort to combat the growing competition from airlines. Originally conceived for locomotive-hauled stock, the first test coaches were built for the prototype HST in 1972, and since, became the main rolling stock of choice for future HST. The Mk3 coaches were built between 1975 and right through to the early 1990s with most surviving (or deritives of) in to the current railway network in 2020.