The BR standard 3MT 2-6-2 tank locomotives were designed to fill the slot between the smaller class 2 tank engines and larger tender engines, many of which were older designs of Victorian heritage. These modern tank engines offered similar power, utility, economy and crew comfort as the GWRs' earlier 45xx design, with which they shared many duties on the Western region.

Sadly like many of the BR standard classes the 3MTs had a short life. Diesel multiple units took over branch, local and suburban services and much local goods business was lost to road transport.