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Rail Data > Articles > Articles list > Article 4: Stock Numbering - Multiple Units
Title:Stock Numbering - Multiple Units
Summary:Details of the numbering of multiple units from 1948 to the present
Added:31st Dec 2019

This article is about the numbering of multiple units sets. For information about the numbering of individual coaches within multiple units ('side numbers'), see the article on coach numbering.
The use of Diesel Multiple Units (DMUs) on Britain's railways before the 1950s was limited to a handful of experimental types. From the mid-1950s onwards, BR ordered large quantities of DMUs for use on all regions except the Southern. As these were not kept in fixed formations, they were referred to by their side numbers alone. The Southen region opted for electric rather than mechanical or hydraulic transmission and several batches of DEMUs were built in the same period. These were kept in formations and they were assigned set numbers in the 1xxx block of the existing Southern numbering scheme (q.v).
Prior to Nationalisation in 1948, the Southern Railway was the only company to have made extensive use of electric multiple units (EMUs). EMUs were operated by the LMS and LNER but these were generally on isolated networks (such as at Merseyside and Tyneside) and the units were referenced only by their side numbers. The Southern Railway adopted 3rd-rail electrification as standard in 1926 and built large quantities of EMUs that were given set numbers in a simple numerical system. Numbers were usually 4-digits, and blocks were allocated numbers sequentially, regardless of type. A renumbering exercise in 1936 attempted to seperate out specific groups (such as express stock) [1] and this system, with some modifications, remained in use for over forty years.
Under British Railways, electrification started slowly with a couple of DC schemes that had been started by the LNER (Liverpool Street to Shenfield, and Manchester to Sheffield). The Shenfield route started in 1949 using multiple units numbered 01 to 92. The Manchester route received just 8 similar units for use as far as Glossop (longer distance services were loco-hauled). When the wiring was extended from Shenfield to Chelmsford and Southend in 1956, new units were delivered numbered 01s to 32s, the s suffix allowing them to be distinguished from the earlier Shenfield units. In 1956 it was decided to use AC electrification for future schemes (other than on the Southern Region) and also to convert the two Liverpool Street routes. It also seems to have been decided that multiple units should have unique set numbers, at least within a given network or region. The Shenfield and Southend units were rebuilt and renumbered as 001-092 and 101-132 respectively.
Several further routes gained AC overhead wiring in the early 1960s, including more lines from Liverpool Street and Fenchurch Street, the West Coast Main Line (WCML) from Euston to Crewe, Liverpool and Manchester and a suburban network in Glasgow. New multiple units were built for each of these, those on the Eastern region using numbers in the blocks 133-165, 201-321, 401-455, 501-519 with express units in the 6xx series. Units for the WCML were 001-045 for the early sections (as far south as Rugby), followed later by 046-095 when the wires reached London. The Glasgow network received units numbered 001-110. As can be seen, the policy of having unique numbers within a region was adhered to. There were (for example) three units numbered 001, but as the Liverpool Street, Manchester and Glasgow networks were not (yet) connected by electrified tracks, there was little chance of confusion.
What became unit 303014 was known as just 014 when seen in Glasgow in 1963. Other units numbered 014 worked from Liverpool Street and on the Birmingham/Manchester network.
The computerised system known as TOPS (Total Operations Processing System) was introduced by BR in the early 1970s and this led to new classifications and numbering for locos and multiple units. As detailed in the article on Unit Classification, EMUs were given class numbers in the 3xx (AC overhead units), 4xx (DC third-rail units on the Southern) and 5xx (DC overhead or third-rail units elsewhere) ranges. DMUs were allocated class numbers in the 1xx (Diesel-Mechanical and Diesel-Hydraulic) or 2xx (Diesel-Electric) ranges.
The intention was that unit numbers would (as with locos unders TOPS) include the class number as well as the serial number. Thus, for example, Southend unit 101 was now in class 307, so its new number would be 307101. In the event, it was to be some time before 6-digit set numbers appeared on existing stock. Hugh Longworth's amazingly detailed book on BR EMUs [1] gives the actual dates of each renumbering. The Glasgow units were done first (in 1979/1980), while the Liverpool Street and Euston/Birmingham/Manchester sets were dealt with between 1980 and 1983 (apart from the class 306 'Shenfield' units, which were due for withdrawal and retained their 001-092 numbers). Although Southern region EMUs were allocated new class codes in the 4xx range, there was no plan to change the existing 3/4-digit set numbers at this stage.
In the event, it was to be some time before 6-digit set numbers appeared on existing stock. Hugh Longworth's amazingly detailed book on BR EMUs [1] gives the actual dates of each renumbering. The Glasgow units were done first (in 1979/1980), while the Liverpool Street and Euston/Birmingham/Manchester sets were dealt with between 1980 and 1983 (apart from the class 306 'Shenfield' units, which were due for withdrawal and retained their 001-092 numbers).
Class 309 unit 607 was seen passing Stratford in about 1981, after it was reduced to 3-cars but before it was renumbered to 309607. Note that the set number is repeated on the ends of the intermediate coaches, a practice which seems to be unique to the Liverpool Street routes (and which can still be seen on class 321 units).
The first AC units built after the introduction of TOPS were class 312 and 313 units ordered mainly for the Great Northern electrification scheme and delivered in 1975-1977. These carried 6-digit numbers from new. As this meant there was no need to have unique serial numbers, the units were numbered 312001 upwards and 313001 upwards. Further class 312 units were ordered for the Liverpool Street lines and for Birmingham. As these were classified as 312/1 and 312/2 respectively, the units were numbered from 312101 and 312201. However, it seems that some staff and operating departments still refered to units by their 3-digit serial numbers, and this could now lead to confusion. For example, there were two units on the Kings Cross lines 'numbered' 001, and two working out of Liverpool Street 'numbered' 101. The solution was to amend the serial numbers of the new units, this being done in 1978/1979. The 312/2s and 313s were left as they were but the 312/0s had numbers 001-026 changed to 701-726 while the 312/1s were changed from 101-119 to 781-799.
Further builds of EMUs in the 1970s and 1980s continued the policy of avoiding duplication of serial numbers within a region. The Merseyside network got 507001-507033 (the older sets did not have set numbers), Glasgow got 314201-314216 (to avoid class 303 and 311 units) and the Shenfield line's class 306 units were replaced by 315801-315861. The first EMUs based on the Mk3 coach bodyshell were the class 317s for the Bedford to St Pancras ('Bedpan') route. Although there were no EMUs on the London Midland Region with unit numbers in the 1xx series, the 317s were numbered 317301-317348, to follow on from 312201-312204. A seeming anomaly was the class 508 units for the Southern Region. All previous Southern units had been given class numbers in the 4xx range and had carried 4-digit set numbers. The new units were numbered as 508001-508043. This seems to have been a policy decision that was later reversed, as the next new units for the Southern were originally intended to be class 510s numbered 510001-510074 but actually emerged as class 455s 5801-5874.
Most of the large fleet of DMUs built in the 1950s and early 1960s were still not kept in fixed formations and so did not have set numbers and were therefore not affected by the introduction of TOPS. However, set numbers had started to be applied to units operated by the Western Region (date unknown but before 1976) and the Scottish Region (1981). The Western units gained three-digit set numbers (grouped by class) with a letter prefix to indicate the area to which they were allocated. The set numbers were not tied to the car side numbers but the initial set numbering was generally done in the order of the side number of (at least one of) the driving cars. To illustrate, cars 50856 and 50858 were allocated to Cardiff and Laira (Plymouth) respectively. 50857 was allocated to the London Midland Region. 50856 became part of set number C316 while 50857 was in P317. The Scottish approach was a combination of the EMU 6-digit numbers and the Westen 3-digit numbers. Each set was assigned a unique 3-digit number, which was prefixed by the 3-digit classification. Examples included 101301 and 116385.
It should be mentioned that several depots on other regions also applied set numbers to first-generation DMUs, notably Buxton, Chester, Norwich Crown Point and Tyseley. These set numbers were either painted on the unit ends or displayed on boards in the driving cab windows.
BR's 'second generation' DMUs were all coupled in fixed sets and they were all given TOPS-style 6-digit set numbers. These started with the prototypes of class 140 (railbus) and 210 (DEMU) in 1981, numbered 140001, 210001 and 210002, followed by prototype Sprinters DMMUs 150001/002 and 151001/002 in 1984/1985. Production examples of the 4-wheeled railbus types were delivered from 1983 onwards and all were numbered from 001 upwards (ie 141001, 142001, 143001 and 144001). Interestingly, there was a plan in late 1988 to amend the set numbers, partly to avoid duplications but also to allow easier identification of units which had gained replacement gearboxes. The class 141 had already started being renumbered into the 1411xx series in connection with a refurbishment programme, 141001-141120 being renumbered to 141102-120/101, the curious pattern being to enable the coach side numbers to relate to the set numbers (141001 was formed of 55502+55522 and became 141102). The new plan was for the types to be renumbered as follows:
141101-141120 to remain the same or to become 141801-141820 if fitted with Voith transmission
142001-142096 to become 142201-142296 or 142501-142596 if fitted with Voith transmission
143001-143025 to become 143301-143325 or 143601-143625 if fitted with Voith transmission
144001-144023 to become 144401-144423 or 144701-144723 if fitted with Voith transmission
The Heaton (Newcastle) class 143 units were all renumbered according to this plan, and a handful of Heaton 142s were given new numbers in the 1425xx series. Although the 143s retained their new numbers, the 142s soon reverted to their original numbers and the overall plan seems to have been abandoned.
More Sprinter types arrived in large quantities from 1985 and were given numbers with unique serials. Class 150/1s 150101-150150 were followed by 150/2s 150201-150285, 155s 155301-155335, 156s 156401-156514 and 158s 158701-158872. The 155s were interesting because in 1990 it was decided to convert them from 2-car units into single units by fitting new cabs to the inner end of each coach. New class number 153 was allocated and the units were numbered 153301-335 and 153351-385. The coaches from 2-car 155301 were now 153301 (coach 52301) and 153351 (57301) and so on. Although the unit numbers of the higher numbered 153 did relate to their side numbers, it was later decided to change the side numbers to match the unit numbers. Thus, coaches 57301-57335 were renumbered as 57351-57385 in about 1994, this perhaps being the only case of side numbers being changed to match unit numbers rather than vice versa.
Coverage of the 1990s to current period will be added shortly

[1] British Railways Electric Multiple Units to 1975 (Longworth, 2015), Page 4

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