Developed in response to growing levels of passenger comfort on airlines and the increase in car usage during the 1960s, the first Mk3 coaches were built for the prototype High Speed Train in 1972 and in 2016 have come to be widely recognised as a safe and reliable design of passenger rolling stock.
The original Trailer First (TF), Trailer Second (TS) and Trailer Buffet Second (TRSB) coaches were delivered in HST sets for the Western Region from 1976, with Trailer Guard Second (TGS) coaches following in 1980. Following complaints from Guards, regarding engine noise in the Power Car Guards' compartments, these replaced the last TS, in all sets, from 1980 onwards.
TRUB cars (Trailer Restaurant Unclassified Buffet) were built from 1978 onwards and were reclassified as TRFB (Trailer Restaurant First Buffet) from 1989/90 on the Western Region.