British Rail introduced the production version of the Mk3 coach in 1975 with improved standards of comfort in response to competition from airlines and increased use of private motor cars.

Designed and built by BREL, initially they were intended as locomotive-hauled stock, but with the development of the High Speed Train (HST), were soon adapted for use at speeds of up to 125mph (220km/h). The first version of the Mk3 coach had actually been built in 1972, with ten coaches produced for the prototype HST.

Mk3 coaches continued to be built until 1988, but multiple units based on the Mk3 body shell were built until the early 1990s. The standard length of a Mk3 coach is 75ft (23m), which is ten feet longer than its predecessor, the Mk2, and is of monocoque construction with an all-welded mild steel stressed skin.

GWR-liveried Mk3 coaches were formed into full-length HST sets and from 2019, in sets of four, to operate as GWR ‘Castle’ sets, which ran as such until May 2024.

This RailRoad coach model represents a Trailer Guard Standard coach in GWR livery.