British railcars and diesel multiple units

The railways were placed under Government control two days before war was declared on 3 September 1939.[16] After the war, the railways were in a poor financial state, with a maintenance backlog.[17] Government control was relinquished when the Transport Act 1947 nationalised most of the railways in the United Kingdom and control passed to the Railway Executive of the British Transport Commission,[18] who inherited 37 diesel railcars.[19] A 1952 report recommended lightweight diesel multiple unit trials, and a memo to the Board suggested diesel railcars could replace push-pull steam trains on 168 routes. After fuel rationing ended, the first order was placed in November 1952 for 21 x 2-car sets built at Derby Works, which became known as Derby lightweights.[20] More were to follow until this class numbered 66 motor cars and 55 trailers.[21] In 1952, British United Traction made numerous 4-wheeled single car railbuses.[22]

A Diesel Multiple Unit in 1983

As part of the 1955 Modernisation Plan of British Railways, plans were made for up to 4,600 diesel railcars.[21] The British Railway workshops at Derby and Swindon did not have the necessary capacity, so private carriage builders such as Metropolitan-Cammell, Gloucester, Birmingham and Cravens received orders.[23] Not all units could work in multiple with each other, but the blue square coupling code covered 84 percent of the cars built, using a four-speed gearbox with gear selection controlled pneumatically.[24] Engines could vary in power output from 150 to 230 hp (110 to 170 kW) and vacuum brakes were used.[25] Internally the units could be classified as suburban with doors for each seating bay and 3+2 seating in second class, such as Class 118, low density with two doors per vehicle side, 3+2 bus style seating in second class, such as Class 114 and Intercity with interiors to the same standard as locomotive hauled stock, such as Class 124.[26]

In 1963, Richard Beeching's The Reshaping of British Railways report recommending the closure of 5,000 miles (8,000 km) of mostly rural branch railways,[27] led to the Beeching cuts and halted the manufacture of new vehicles.[28]

As of 2012, about 250 vehicles survive in preservation,[29] and various vehicles (mainly 101s and 121/122s) survive in departmental use.

Diesel electric multiple units were introduced on the Southern Region, where there was experience of DC electric multiple units. The Hastings line had special restrictions due to tunnels on the line and special narrow stock was needed. The six car sets had two power cars, each having 500 horsepower (370 kW) diesel generator driving two standard Southern Region 250 horsepower (190 kW) traction motors.[30] Introduction had been planned for June 1957, but special services were run early following a fire at Cannon Street in London. When the full timetable started 12-car trains divided en route into non-stop and stopping portions.[31] Elsewhere the standard loading gauge could be used and the trailer vehicles were similar to contemporary Southern Region electric multiple units.[32] Two car sets were built for local services on unelectrified lines in Hampshire, followed by three car sets, for which the generator was uprated to 600 horsepower (450 kW).[31]

A Midland Pullman in 1960

The Blue Pullman was a class of high-speed luxury diesel-electric multiple units introduced in 1960. Six coach sets were used on the London Midland Region, all first class with at seat service served from two kitchen cars. The two power cars had diesel engines connected to a 870 hp (650 kW) generators, both supplying four 199 hp (148 kW) traction motors. The Western Region units had two additional second class coaches. All cars were double glazed and air-conditioned, the first on British Railways.[33]

There was a desire in British Railways for faster trains, but none of the main-line diesel locomotives could achieve anything faster than 100 mph (160 km/h). It had been calculated that 4,000 hp (3,000 kW) was needed, and after the Paxman Valenta engine with an output of 2,250 hp (1,680 kW) became available, a prototype train with two Class 41 power cars and standard Mark 3 coaches was built.[34] In 1973 this prototype achieved 143 mph (230 km/h), and production InterCity 125 trains entered service in October 1976, becoming the first 125 mph (201 km/h) diesel train service in the world. Initially the rolling stock was considered to be diesel-electric multiple units, with coaches sandwiched between two power cars.[35]

Two prototype Class 210 DMUs were introduced in 1981, based on the Mark 3 coach bodyshell with a diesel engine mounted at the end of one of the driving cars. It was not a success due to complexity and cost.[36]

The Pacer series grew out of a single car prototype developed for export that used a body designed by Leyland Motors with bus components mounted on a 4-wheeled high-speed freight underframe.[37] Two car production units were introduced into Britain from 1981[38] to 1987.[39]

A 1980s Northern Rail Class 150 Sprinter at Knutsford

A prototype Sprinter was built in 1983, based on the Mark 3 bodyshell design. The British Rail Engineering Limited Class 150 with a high density layout, followed by the 150/2 that had gangways between units.[39] The Leyland Class 155 and Metro-Cammell Class 156 were built in 1987–89[40] and most Class 155 units were split into two single car units in 1991–92, (becoming Class 153), a new compact cab being fitted to the inner ends by Hunslet.[41] The Class 158 was built for long distance routes with air conditioning and a quiet interior. Upgraded versions of the Class 158, the Class 159 were built for Network SouthEast for use on the West of England Main Line between Exeter and London Waterloo.[42]

The Networker Turbo was built for Network SouthEast in the early 1990s. The Class 165 is a two or three coach unit used on local services on Chiltern and Thames routes out of London and was followed by the 90 mph (140 km/h) Class 166 for long distance services.[43][44]

A First Great Western Class 180

Train manufacturer British Rail Engineering Limited was privatised in 1989,[45] and between 1994 and 1997 the rest of British Rail was privatised.[46] Ownership of the track and infrastructure passed to Railtrack on 1 April 1994; afterwards passenger operations were franchised to individual private-sector operators and the freight services sold outright.[47] Rolling stock is owned by ROSCOs and leased to the train operators; competitive tenders are invited from manufacturers for new trains. During the privatisation process, there was a gap of nearly three years during which no new rolling stock orders were placed. The first new order placed was in June 1996 for four Class 168 Clubman DMUs for Chiltern Railways. These were a development of the Networker Turbo design already in use by Chiltern and other operators.[48]

The Bombardier Turbostar was an evolution of the Class 168 and purchased by Anglia Railways, Central Trains, Chiltern Railways, Hull Trains, London Midland, London Overground Rail Operations, ScotRail, South West Trains and Southern. As at September 2020, they are operated by Abellio ScotRail, CrossCountry, Govia Thameslink Railway, Northern Trains, Transport for Wales Rail and West Midlands Trains.

Alstom Coradia units were built in between 1999–2001. The family consists of the 100 mph (160 km/h) Class 175 (27 units), built for First North Western and currently operating for Transport for Wales Rail and Class 180 Adelante, (14 units), a 125 mph (201 km/h) high-speed unit built for First Great Western and as at September 2020, operated by East Midlands Railway and Grand Central.[49]

The Siemens Desiro Class 185 is in service on TransPennine Express services. The 51 strong fleet was built between 2005–2006 for First TransPennine Express.[50]

The Bombardier Voyager family is a series of high speed DEMUs. Virgin CrossCountry were looking to replace a mixture of life expired loco-hauled trains and mid-life HSTs and have tilt for use on the West Coast Main Line. The result was the non-tilt Class 220 Voyager and tilting Class 221 Super Voyager. As at September 2020, they are operated by Avanti West Coast and CrossCountry. Midland Mainline and Hull Trains ordered the Class 222 Meridian non-tilt version. As at September 2020, all are operated by East Midlands Railway.

As part of the Intercity Express Programme bi-mode Class 800 and 802s entered service on the Great Western Main Line in 2017 and on the East Coast Main Line in 2019.[51]

Diesel CAF Civity DMUs have been ordered by Northern (Class 195), West Midlands Trains (Class 196) and Transport for Wales Rail.[52][53] Abellio Greater Anglia have ordered bi-mode Stadler Flirts.[54]

Bi-mode Class 769s are being converted from Class 319s for Great Western Railway, Northern and Transport for Wales Rail.[55] Diesel-electric and diesel-battery-electric Class 230s are being converted from London Underground D78 Stock for Transport for Wales Rail and West Midlands Trains.[56]

Train manufacturer in the UK and other rail reliant countries that use DMU rail cars must be refuelled at depot stops with diesel. The refuelling process is usually carried out by a qualified operator with knowledge of rail refuelling. The train driver would usually level the train up to the platform to meet the refuelling pipes assigned at measured distances according to the length of the DMU and the refill nozzles. A Rail Refuelling Flyte Coupler[57] is used to connect the DMU to the fuel line. It is a screw in connection with a safety dry break mechanism to stop accidental leaks. The flow of fuel needs to high volume but low pressure to ensure the fuel does not overfill. Usually there is a float arm similar to a toilet cistern that cuts off the refuelling once a predefined level is reached, however if the pressure is too high, this can cause the train tank to overfill and leak fuel.