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Diesel Electric Multiple Units (DEMUs)

NB The sketches used for illustration are NOT scale drawings - Illustrations, where provided, are sketches not scale drawings and were intended to show the various livery changes, so matters below the solebar tend to get rather impressionistic. I have to admit I have little interest in or information on the DEMUs and I am deeply indebted to the members of the uk.railway and uk.rec.models.rail newsgroups who have provided a great deal of the information and, sadly, many corrections for the text.

Note There is a fore-shortening effect when a locomotive is viewed from the normal 'three quarter view' angle, making it appear rather shorter than it is. The photo below shows this effect. When preparing sketches I have tried to find photographs to work from taken at as flat an angle as I was able however this has not always been possible.

Model of a BR HST 125 locomotive
Model of a BR HST 125 locomotive
Photo of model courtesy Ian and Sandra Franz

Diesel electric multiple units (DEMUs) are fitted with electric traction motors powered by an on board diesel engine driving a generator. There have been a few petrol engined units using the same principle, indeed the two NER petrol electric railcars introduced in 1903 are the oldest examples of the type I have yet identified. Built at York in 1902 and referred to as 'autocars' they operated on several lines in the North East, one got a new engine in 1922 (enabling it to pull a standard passenger coach) but both were withdrawn from service by 1931. One got sold off for use as a shed, No. 3170, and this has now been recovered by carriage restorer Stephen Middleton. He has set up a charitable organisation to restore this historically rather important vehicle, I am trying to avoid links on the main pages of this site (too difficult to maintain) but a search on '1903 Electric Autocar Trust' should turn up information on this project.

NER Petrol Electric Railcar of 1903
Sketch of the NER petrol electric railcar

The Great Central Railway also operated at least one petrol electric railcar although I have not yet traced any details on this unit.

The first diesel powered multiple unit on British lines was a four car DEMU set built in 1927 for the LMS. At that time the transmission systems available were unsuitable for a diesel engined railway vehicle (other than small shunting engines or very lightweight 'railbus' vehicles). This single unit was made up of two two-car EMU sets, built in 1913 for the L & Y Bury to Holcombe branch north of Manchester. This line had been electrified using 3500 Volts DC and an overhead supply but in 1917 the L & Y converted the branch to third rail operation and built new stock to suit. Ten years later the original sets were converted into a single four car unit by English Electric, a 500hp engine and associated generator was fitted to one of the power cars and the set operated between Blackpool and Lytham for about a year (1928-1929). The sketch below is somewhat provisional but I believe it is correct (it is based on one rather poor quality low resolution photo where I believe this unit was in the background).

LMS 4-car DEMU of 1927
Sketch of the LMS DEMU

Between 1931 and 1932 Armstrong Whitworth built three 60 feet long diesel-electric single railcars using their own four stroke engies coupled to GEC electrical gear. The three units were called 'Tyneside Venturer', 'Northumbria' &'Lady Hamilton'. These units saw service on the LNER and LMS lines, the LNER actually purchased 'Tyneside Venturer' and repainted it in their livery (retaining the long A.W. makers plate but painting this over), but I have found no references to them after the mid 1930s.

Armstrong Whitworth DEMU in LNER livery
Sketch of the Armstrong Whitworth DEMU in LNER livery

Mechanical transmission systems are not suitable for the loads imposed by the high speed intercity units so diesel-electric transmission was selected by BR units employed on these duties. The DEMU transmission system was also applied to a small number of units operating from London into Kent and Hampshire (where the staff and workshops were geared up for electric traction motors but electrical supplies had not yet been implemented on all lines).

BR(S) DEMU types
Thanks are due to Colin Wats for pointing out the errors and omissions in this section

All the Southern Region DEMUs were known by enthusiasts as Thumpers due to the noise they made. As far as I am aware all the diesel electric multiple units date from after the nationalisation of the railways.

The Hastings Line
The line to Hastings line had very tight clearances due to the tunnels south of Tonbridge; even tighter south of Tunbridge Wells. Substandard in construction these tunnels had to be fitted with additional brick linings requiring any stock for the line had to be made slightly narrower than for other lines, usually done by modifying the profile of the side and resulting in a rather slab sided appearance on the Hastings units and a narrowing of the Oxted units (which ran only as far as Tunbridge Wells). The latter profile isn't too obvious but my own interest is not DEMUs.
(This was not the only line with such a problem, the old Maryport & Carlisle line also had a restricted gauge and Derby Lightweight DMUs were built in a special narrow bodied version (3 inches smaller than standard) to serve this line).

Class 201 (6S), 202 (6L) & 203 (6B) 'Hastings' Units
These were six-car diesel sets introduced from 1957 for the Hastings services. The original 6S (1001-1007) units were built on 58' underframes having one window seating-bay less that the subsequent 6L units (nos.1011-1019). The 6B units (nos. 1031-1037) incorporated a Buffet car into the 6L design. Besides Hastings to Charing Cross for many years the 6B units operated a Saturdays-only Brighton to Exeter service. Currently one Hastings unit survives in preservation and is possibly the oldest train on the main line network still operating out of its original purpose-built shed at St Leonard's West Marina. The six-car Hastings units were the first to use red headcode blinds instead of carrying tail-lamps. Note the bodysides are vertical and flat, rather than bowed out as on most passenger stock. This was not the only line with such a problem, the old Maryport & Carlisle line also had a restricted gauge and Derby Lightweight DMUs were built in a special narrow bodied version (3 inches smaller than standard) to serve this line.

Sketch of the Hastings Thumper in BR Blue Greylivery

Note the sides are vertical and flat, rather than bowed out as on most passenger stock.

Class 204 3T
Three-car units being 2H units lengthened to three-cars by the insertion of driving trailer coaches from disbanded 3R Tadpole units. The driving compartment was rendered inoperative and the full yellow end of the former cab front repainted blue.

Class 205 2H & 3H Hampshire, Hastings and Berkshire Units
Two and three car units originally used in Hampshire and the Hastings area. 1957 built Hampshire units 1101-1118 were introduced as 2-car sets although subsequently had trailer coaches added. 1958 built Hastings units remained as two-car sets for many years; these originally being intended for use on the Bexhill West and New Romney branches near Hastings. Following closure of these branches the term `Hastings' fell into disuse. 1959 built Hampshire units were built as three-car sets as were the 1962 built Berkshire units (these having only four compartments in the Driving Motor Brake Second as a consequence of a large guard's van area). A kit is available from BH Enterprises

'Hampshire Thumper' 2H set
Sketch of the Hampshire Thumper in original livery

(Note: The unit on the left is incorrectly carrying a 6-car Hastings 6S unit 2-digit headcode - Sadly I do not know a correct code for these usnits)
Point to note is the orange V shape which indicated `NO BRAKE VAN AT THE OTHER END OF THE UNIT' carried on the Driving Motor Brake Second and was originally there to help staff dealing with mail at Winchester quickly identify the correct end of an approaching train. When the small yellow warning panels were introduced in the mid-1960s it was replaced by an inverted black triangle as shown on the right and adopted on all the Southern Region's two and three-car units (i.e. those with a brake van only at one end). When the full yellow ends appeared the black triangle was retained into the privatisation era.

Class 206 3R
These three car units (numbered 1201 to 1206) were known as Tadpoles as they each had a narrow bodied (former `Hastings' 6S /class 201) Driving Motor Brake Second and Trailer Second coupled to a standard bodied ex EMU Driving Trailer from disbanded 2 EPB units. Note the sides are vertical and flat, rather than bowed out as on most passenger stock.

Class 207 3D
1963-built three car East Sussex (later known as Oxted) units and were originally numbered 1301 to 1319. These had a reduced but still curved body profile for operating through the narrow tunnels between Tunbridge Wells and Tonbridge. Towards the end some of these units had their centre cars removed or replaced with Trailer Seconds from former 4 CEP electric units. The 3D units never carried an orange V but were later equipped with inverted black triangles. The sketch below is based on a photograph of an Alpha Graphics N Gauge kit of the type showing early Connex livery. A kit is available from BH Enterprises Two and three car Oxted units. The sketch below is based on a photograph of an Alpha Graphics N Gauge kit of the type showing early Connex livery. A kit is available from BH Enterprises

Class 207 in Connex livery
Sketch ofClass 207 in original Connex livery

High speed inter city diesel multiple units
These units employ electric traction motors powered by a diesel engine, making them a DEMU, although they are never referred to as such they have Class numbers falling into the DEMU series. Curiously the older BR built units (blue Pullman and HST 125) have higher numbers than the more modern Privatisation era units. Thanks are due to Martyn Roberts and John Turner, both denizens of the uk.rec.models.rail newsgroup, who provided a lot of additional information on the modern DEMU sets. John's photo website is well worth a visit to see liveries in everyday use (see listing in Appendix Six - Contributors and Bibliography).

Class 210 Voyager
Class 210 was a prototype DEMU unit based on the Mk 3 passenger coach but they were considered too expensive (in the event the Govt accepted the Class 150 DMUs instead, although they did decide these should be two-car units not the planned three car sets).

Class 220 Voyager
These four coach diesel-electric units were built by Bombardier for by Virgin Cross Country to replace elderly HST sets on their cross country services. They can operate in multiple but the design of the ends means passengers cannot walk from one set to the next. They cannot operate in multiple with the Pendolino as they have different couplers (they can work with the tilting Class 221 Super Voyagers however).

Photo of a Class 220 Voyager

Class 221 Super Voyager
These five coach diesel-electric units were ordered by Virgin to replace elderly HST sets on their cross country services. They have a tilting ability similar to the Pendolino but cannot work in multiple with that class as the couplings are different. They can operate with the Class 220 but the latter do not tilt and hence the maximum speed of the combined unit would be that of the 220.

Photo of a Class 221 Super Voyager

Class 222 'Meridian' and 'Pioneer'
These 200kph four-car sets were built for Midland Mainline in 2004 and are based on the Voyager series but have a different front end design, according to the makers they are 80% different but this is hard to quantify. The Meridian sets were purchased to replace Class 170 Turbostars (which were transferred to another company). Another company based in Hull has acquired some 4-car Class 222 sets, which entered service in May 2005, although they call them 'Pioneer'. The sketch below shows the Midland Mainline blue white and grey livery.

Sketch of a Class 222 Meridian unit in Midland Mainline blue livery

Class 251 and 261 introduced 1960, all withdrawn by 1973
Class 251 and 261 are the Blue Pullman sets introduced in 1960 and operating into the 1970s. The 251 cars are the driving motor trailers, the inner cars are class 261. These units were built by Metropolitan Camel for high speed inter-city work and were delivered as six and eight car units. They used a MAN engine design built under licence by North British Locomotive Works and were the first trains in the UK to be fully air conditioned. Offering a maximum speed of 90mph and very high levels of comfort they were rather let down by their bogies which gave poor riding characteristics at high speed. They broke with tradition in not having curtains on the windows, instead there was a venetian blind sandwiched inside the double glazed windows, operated by a handle under the window. Undoubtedly luxurious by the standards of the day (and pretty impressive by today's standards as well) they failed to meet the needs of the network. Only five sets were built, the two 6-car sets were used on the London Midland line between Manchester and London and the three 8-car units went to the Western Region for trains from South Wales to London and Birmingham.

Blue Pullman (original livery)
Sketch of the Blue Pullman in original livery

All the LMR sets were transferred to Western region 1966 following the electrification of the Manchester to London line. At some point they received full yellow ends, rather spoiling their appearance in my view. The whole fleet were withdrawn by 1973. Sadly none have been preserved.

Class 252
Class 252 was the High Speed Diesel Train, in effect the prototype HST unit, which looked rather like the APT but had a flat-fronted driving cab at the inner end as well as the streamlined front cab. This unit had buffers on the ends and, in 1973, was operated in a rather neat livery (both power cars and coaches) of light grey with a dark grey window band and a band of yellow across the cab front.

Sketch of a Class 252

The sketch is based on a single photograph and may be inaccurate in detail. The lights are mounted behind the lower windscreen. By 1980 the whole of the front was yellow, including the roof, to the line of the drivers door, the remainder of the train was still in the light grey with dark grey band livery.

Class 253 Introduced 1976, still in use in 2005
This was the original designation for the High Speed Train or HST125 (capable of 125 mph on suitable lines). The HST's replaced the loco hauled services that had replaced the Class 251 'Blue Pullman' sets on the London-Bristol to South Wales lines. The coaches used on the initial services were in BR standard blue and grey express passenger livery of the period. These units were iconic with their modernistic styling and improved passenger comfort.

High Speed Train (original livery)
Sketch of the HST 125 in original livery

The HSTs were originally designed as fixed rakes and designated as 'Class 253 diesel multiple units', each set had a power car at each end with eight coaches between, hence if one power unit failed the train could still complete the journey albeit at reduced speed. They were later reclassified as Class 43 locomotives and standard Mk.3 coaches and by the mid 1980s there was a move to running five car sets with a single power car, three coaches and a driving trailer coach. This meant that should the power car fail the train would have to be rescued by another loco, and at the time the reliability of the existing units was a matter of some concern. Mick Bryan on the uk.rec.models.rail newsgroup was able to advise-
Full HST sets with only one power car were capable of nudging the ton unassisted. However, they had to be loco-assisted over the Devon banks if one Power Car was dead.
The HST uses buckeye couplers within the set but there are no buffers on the power cars, although there is a coupling attachment point hidden behind the rectangular panel on the underside of the front and this can be used with a rigid bar coupler. In use the rectangular panel lifts upwards to stand vertically on the nose with the bar projecting from the exposed pocket. I was not sure how this worked in practice so I asked on the uk.rec.models.rail newsgroup and received the following detailed answer.
Been there, done that, dropped the B****Y bar on my foot too.
There are two coupling bars carried in the guards van. A short one for an HST-HST couple, the other longer bar was for a loco-HST couple. The HST nose door lifts up to reveal a couple of very long air brake hoses and a short bar with an eye on the end. The coupling bar has a fork on the end which fits over the eye and is connecting by dropping in a large pin. The large pin is secured with a smaller pin and (IIRC) an "R" clip. The other end of the HST coupling bar has a similar forked end to fit over the eye of the assisting HST. The loco coupling bar has a fixed cross-bar on the end, rather than a pin, which goes over the loco hook. There is a pin but it goes in front of the loco hook jamming the loco hook between cross-bar and pin. The cross bar is big enough to not jump out while propelling.
This is a lot easier said than done, especially in the dark. It requires some quite nifty driving on the part of the assisting loco too - there is a certain amount of slack in the bars (which can be increased by removing a couple more pins) but only about 3" from memory. The Neville Hill shunt drivers we used to practice on were very tolerant of fools, but a request to "ease up 2 inches mate" to the driver of an 08+barrier coach+dead HST power car combo was likely to be met with a raspberry. Good fun though !
Lastly, a quote from a then Area Ops Mgr - "APT might have been unreliable but at least when you opened up the nose it had a proper set of genitalia underneath".
Stuart (ex- Operating Supervisor)
I understand that these coupler bars will not work with buckeye type couplers so GNER HST sets also carry a special adapter to allow them to be rescued by the swing-buckeye equipped Class 66 and Class 67 locomotives used by this company as 'thunderbirds' (rescue engines).

The original HST livery was replaced in the 1980s by the rather more stylish 'executive' livery.

High Speed Train (Executive livery)
Sketch of the HST 125 in Executive livery

The HSTs have continued in use after privatisation, sets being operated in the colours of GNER, GWR (later FGW, these units were fitted for ATP), MML, NR, and Virgin (cross country). They became less common as the new multiple units arrived, by 2005 comparatively few were in service but units are (in 2005) being reconditioned and offered for further use.

In 1989 eight power cars were fitted with buffers and screw-link coupling facilities, at which time they were in Intercity Executive livery as shown above. This was done so the first 10 examples of the Class 91 locomotives could be tested for their intended push-pull role. At the time there were no Mk 4 coaches available so the Mk 3 coaches of the HST sets were modified to carry the Time Division Multiplex control system (operating via the lighting circuits on Mk 4 coaches)to test the loco remote control system. The second HST power car had to be used as the driving trailer as the HST uses a non standard 3-phase 415v heating and lighting circuit which the Class 91 could not supply. The plan was for the Class 91 to provide traction with the HST power car providing ETH (Electric Train Heating) supply but in practice this car was also used for traction, providing quite remarkable acceleration. At some point two of the buffer-fitted HST power cars were coupled together to produce a double ended locomotive which was then used during trials of the new Mk 4 coaches. This set was in use in 1991 and there is a photograph on John Turner's website (see Appendix Six). After these trials all the modified HST units were returned to normal service but retained the buffers and couplings.

High Speed Train with buffers (Intercity 'Swallow' livery)
Sketch of the HST 125 in  Swallow livery

After a time on the ECML the remote control gear was removed but the buffers remained and the cars became part of the Virgin cross country fleet, I gather at least one pair of these ended up in GNER colours. HST sets without buffers could be rescued by conventional locomotives employing the HSTs coupling bar, also if the lights on the front of the HST failed the rules required a locomotive with working lights to act as 'pilot' running at the front of the train.

One final variant is the Network Rail New Measurement Train, based on a pair of HST power cars equipped with buffers at either end of a rake of four coaches and introduced in July 2003. This unit serves the same purpose as the Wickham railcar illustrated above but whereas the Wickham beetled about at 30 mph this set runs as 125 mph.

HST Network Rail 'New Measurement Train'
Sketch of the HST 125 in original livery

As well as having buffers the rearmost window behind the guards door has been plated over and some sort of gizmo is mounted below the drivers window. This box has a glass covered window in the lower front part which I understand houses a video camera. The rake consists of two power cars, 43014 and 43062 with a Mk 2F coach (975984) and at least three Mk 3 coaches (977974,999550 and 975814) and provides not only measurement readings of the track and between-track six foot way but even has a conference room (able to take 12 delegates). The train has a fortnightly schedule covering all the countries main lines (although not on Southern Region) and its high speed allows it to operate slotted in between other services on the line.

Class 254
The class 254 was used on the ECML, and was the same as a 253 but had an extra coach either a TSO or a second buffet car. Oddly the two buffet cars were often not marshalled together but were positioned separately in the rake.

Class 255
Refurbished HST sets likely to be used on a London Birmingham service.

Class 261
Inner cars from the Blue Pullman sets, see Class 251 above.


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