The Great Western Railway (GWR) 6400 Class is a class of 0-6-0 pannier tank steam locomotive introduced by Charles Collett in 1932. All 40 examples were 'auto-fitted' – equipped with the remote-control equipment needed for working autotrains. The 1936 GWR 7400 Class was a similar class, without the autotrain apparatus, but with a higher boiler pressure of 180 psi, providing a small but useful increase in power. An initial build of 30 in 1936-1937 was added to by British Railways in two batches each of ten locos in 1948 and 1950. These were destined for a short life, the briefest being only nine years. A minor visual difference between the 5400 and earlier 6400, and the later series of 6400, with the 7400 classes was at the join between cab and bunker. The 5400 and early 6400 had an arc whereas the later 6400 and the 7400 class was straight. The early locos also had a lip at the leading edge of the cab roof, whereas the later locos had a plain corner edge. Both classes were closely related to the 1930 GWR 5400 Class, which was in turn an evolution of both the Armstrong 1874 GWR 850 Class and the Dean 1891 GWR 2021 Class. Thus the basic design was almost sixty years old when new, the 4 ft driving wheels being the main distinguishing factor, apart from the more modern profile. There were also superficial similarities with the GWR 645 Class as extant in the 1930s, that also had 4 ft wheels and 24 in stroke cylinders (and by then pannier tanks and full cabs).

Operations

The smaller wheels of the 6400's permitted operation in hillier locations than the 5400 Class and allocations were initially to the South Wales valleys. Engines of class 6400 worked on many of the ex-GWR branch lines in Devon and around Plymouth until the early 1960s, when the lines closed or diesel multiple units took over services. No. 6430 was a regular engine on the old Tavistock South branch line and would often run with two autocoaches. No. 6412 was allocated at Gloucester Horton Rd loco shed (85B) and operated one of the last 'Chalford Railcar' autotrain services between Gloucester and Chalford on 31 October 1964. Being allocated to Plymouth Laira the type was trialled on the former Lostwithiel and Fowey Railway, although a 1400 Class 0-4-2 engine was normally used.

Withdrawal

The below list shows when all of the original 6400's and later 7400's were withdrawn from service. The members of the GWR 6400 Class and the GWR 7400 Class were No. 6419 and No. 7439 respectively.

Preservation

Three of the 6400 Class have survived to preservation: