British Rail locomotive and multiple unit numbering and classification
A number of different numbering and classification schemes were used for locomotives and multiple units operated by British Railways (BR), and this page explains the principal systems. This section also covers the post-privatisation period, as the broad numbering and classification arrangements have not altered since the break-up of BR. Locomotives and multiple units (the majority being self-propelled) have frequently had similar arrangements for classification and numbering, so are considered together here. There are also links to other pages that deal in greater depth with the particulars of individual  types. Constituent companies. In 1948, BR inherited a variety of locomotives and multiple units from the Big Four railway companies and some smaller concerns. Details of the numbering and classification systems used by the Big Four companies are covered in the following pages: In the main, new locomotives and multiple units built by BR to pre-nationalisation designs were numbered and classified according to the principles applied by the relevant Big Four company. 1948 numbering and classification. Immediately after nationalisation, BR had to decide how to number and classify the stock it had inherited from the Big Four companies, and  how newly built stock would be included. In the main, it decided to simply adapt what was already there. Locomotives. The classification systems of the Big Four were left unchanged for the inherited locomotives. However, BR decided to adopt the LMS power classification system as its preferred model and all inherited locomotives received a classification in this series as well as their traditional classification. In order to remove the duplications of locomotive numbers, all locomotives were placed into a new number series as follows: "Note:" *Isle of Wight locomotives retained their existing numbers in a separate series commencing at W1 , and locomotives transferred to the island by BR were renumbered into that series - and vice versa for those returned to the mainland. This approach meant that the numbering arrangements adopted by the pre-Nationalisation companies were retained in the new system, and new locomotives built to the designs of the old companies were numbered appropriately in their series. Locomotives inherited from smaller concerns were numbered in the most appropriate regional list, e.g. ex-East Kent Railway stock utilised blank numbers in the 3xxxx ex-SR series. The new series for diesel, petrol, gas and electric locomotives were arranged as follows : Note: * Number 13000 was initially allocated to a 250 hp (186 kW) ex-LMS shunter, but this locomotive was withdrawn before being renumbered. Modern traction. Numbering of electric multiple units was undertaken on a regional basis, with each region having its own series commencing from 001. Most diesel multiple units were not allocated unit numbers, though in later years numbers were allocated on a regional basis in the Scottish and Western regions, and by individual depots elsewhere. For more details on these series, see British Rail Regional Multiple Unit Numbering. To classify electric stock, a two-letter prefix was used  to indicate what type it was, followed by a number issued sequentially from 1. This was a system adapted from that used by the LNER for its electric stock (e.g. EM1, see here). The additional prefixes used were: The Eastern and North Eastern regions used a series of different classifications for diesel locomotives. The first method was also adapted from the old LNER system, and applied only to diesel shunters operating on those regions. It comprised a prefix, indicating the transmission type and wheel arrangement, followed by a number allocated sequentially from 1. The prefixes used were: The second classification  system was developed in 1955 and applied to all types then in existence on British Rail. It was based on the format Dx/y, where x was the power of the locomotive in hundreds of horsepower and y was a number allocated sequentially to specific types (e.g. D1/1 would be a shunter with a 100 to 199 hp (75 to 148 kW) rating, D33/1 would be a Type 5 locomotive). The series was extensively re-arranged in 1962 in a somewhat confusing way, but following the same basic principles. The Southern Region followed existing numbering (for its multiple units) and  classification systems (for both multiple units and locomotives) inherited from the SR. The EMU classification system (e.g. 4SUB, see here) system was also extended to include their diesel-electric multiple units, but with a single letter. Locomotives were given a two-letter code, with the second letter indicating detail differences within the main type. For instance, what were to become Class 33 locomotives from 1973, were Class KA or KB depending on whether they were the standard design or that fitted for push-pull working with 4TC units. 1957 numbering and classification. In the early period of British Railways, steam  locomotion had continued to be of prime importance. Apart from a growing selection of diesel shunters, there had been almost no development of mainline diesel or electric traction beyond the few locomotives ordered by the Big Four companies. The 1955 Modernisation Plan heralded big changes in this situation, and from 1957 a new numbering system was used for diesel and electric locomotives ordered by British Railways, including those shunters ordered before 1957, which were renumbered into the new system. All steam and gas-turbine locomotives, and diesel and electric locomotives built to pre-nationalisation orders retained their existing numbers under  the 1948 arrangements, though some had a 'D' or 'E' prefix added to their number in error. Diesel locomotives. The numbering system matched up the new 'Type' classification that had been adopted for diesel traction, and which was based on the power of the locomotive. The broad categories were as follows: Of the shunters that were renumbered, the only transparent renumbering was for those that had been numbered in the 13xxx series, for which the '1' was simply replaced with a 'D'. All the others were completely renumbered to separate out the different classes. As always, there were some oddities . The 650 hp diesel hydraulic locomotives later Class 14 were numbered from D9500 upwards. When the Type 2 series got too crowded later on, new Sulzer Type 2 locomotives (later class 25) were numbered from D7500 upwards. Some experimental locomotives carried D0xxx numbers. When the last mainline steam locomotive was withdrawn in August 1968 (leaving only three on the self-contained narrow gauge Vale of Rheidol Railway), the 'D' prefix was dropped. Electric locomotives. The numbering system was divided into two series, one for AC locomotives and one for DC locomotives. DC locomotives were numbered from E5000 upwards, and DC  electro-diesel locomotives, with a diesel generator for working off electrified lines, were numbered from E6000 upwards. For AC locomotives, the first number was to be an indication of power. For example, if the power was in the range 2000 to 2999 hp, it would be numbered between E2000-E2999, and so on. In fact, apart from E2001 (the prototype AC locomotive, converted from a gas turbine locomotive, later Class 80), all AC locomotives were numbered from E3001 upwards. When new 5000 hp locomotives were under construction (later Class 87), these were allocated numbers from E3201 upwards, though they never  carried these numbers as the 1973 arrangements were already in place by the time the first one was built. 1973 numbering and classification - TOPS. At the end of the 1960s, British Rail adopted the Total Operations Processing System (TOPS), a computerised system developed by IBM, the Southern Pacific Transportation Company and Stanford University in the United States. All types of locomotive received a TOPS classification, and multiple units were later included according to this broad division: From late 1970, British Rail started to apply new numbers to locomotives and multiple units based on the TOPS classification system, the first classes  to be dealt with being the LNER-design EM1 type (TOPS class 76) and the AL3 and AL4 types of AC electric locomotives (TOPS classes 83 and 84). The format of these numbers is xxxyyy, where xxx is the class number and yyy the unique identifier for that locomotive or unit. All locomotive classes have unique identifiers that commence at xx001, except classes 43 (High Speed Train power cars, originally classified as multiple-unit vehicles), 97 and 98 (departmental and steam locomotives). Multiple unit classes are treated differently, because an attempt has been made to give units working within the  same region or sector unique identifiers (for more information see British Rail Regional Multiple Unit Numbering). In recent years, unit numbers have also been tied in with the numbers of the carriages within a unit (e.g. 150201 is formed of carriages 52201 and 57201). As a result, very few multiple unit classes commence from xxx001. Where there are variations within a class, subclasses are used in the format xxx/y. When the main renumbering scheme was published in 1973, many sub-classes were redesignated to better align the locomotives to be numbered in that sub-class with the sub-class  number. Thus, class 47 was originally divided into sub-classes 47/1 (locomotives fitted with steam-heating equipment), 47/2 (not fitted with train-heating equipment) and 47/3 (fitted with electric train-heating equipment), but in 1973 these sub-classes were redesignated 47/0, 47/3 and 47/4. Usually, the subclass is connected to the first digit of the unique identifier, so that the first locomotive in subclass 47/3 was 47301. However, some caution is required on this point for the following reasons: So far as renumbering from the 1957 arrangements was concerned, most locomotives retained the last two digits of their number, though  some classes were renumbered without reference to their previous numbers. This was usually where sub-classes had already been or were in the process of being created (for example classes 45 and 47, in which some members were being fitted with electric train heating equipment, and 86, subject to various modifications, mainly to the suspension). The other exception was if the first locomotive of a class had carried a number ending in "00" under the 1957 arrangements, because TOPS could not handle numbers ending in "00". These were either renumbered at the end of the class (e.g. the prototype class  50 D400 became 50050), or took a vacant number of another class member that had already been withdrawn (e.g. prototype class 24 D5000 became 24005, D5005 having been withdrawn in 1969), or were renumbered at the end of a sub-group within the class. Class 20 was particularly complicated in this respect. The class had been built in batches between 1957 and 1967 and all 228 members were still in service when the TOPS renumbering scheme was drawn up, but instead of class prototype D8000 being renumbered 20228 at the end of the class (which was not divided into sub -classes) it became 20050, displaced D8050 became 20128, and D8128 in turn became 20228. The situation was different for multiple units. Where unit numbers were carried, they were usually three-digit already. TOPS simply prefixed these existing unit numbers with the newly allocated TOPS class number. The process was more complicated on the Southern Region, which used four-digit unit numbers and where a more general unit renumbering was required so that the first number of the unit coincided with the last digit of the class number. Many diesel multiple units were not kept in regular formations, so did not  have existing unit numbers, and this situation was not changed under TOPS (except following refurbishment). The TOPS system has been perpetuated by the privatisation of British Rail, though the allocation of classes and numbers appears to have become more random and less governed by the rules followed by British Rail (but even they made exceptions). See British Carriage and Wagon Numbering and Classification for an explanation of how TOPS applied also to carriages and wagons. Please Note: This section explains the successful application of TOPS to multiple unit stock, the arrangement that persists today. However, there was an earlier attempt  to apply TOPS that differed from the arrangement set out below. More details about the first arrangement may be found here. Locomotives. The series of locomotive classes were allocated according to the following pattern: The following table shows in more detail how the classification of diesel locomotives was overlaid on the 1957 classification by Type: AC electric locomotive classes AL1 to AL6 became 81-86 in order. Class 01 was subsequently reused to register any ex-industrial/Ministry of Defence shunters used on the national network regardless of horsepower. Multiple units. The multiple unit series were divided up as follows : AC electric multiple units AM1-AM11 became 301-311 in order (in fact the AM1 units had already been withdrawn, so Class 301 was never actually used). The 1xx and 2xx series were originally arranged so that driving motors, driving trailers and trailer cars all had their own individual class numbers (presumably because these units were more prone to being reformed), but this was subsequently revised so that each type of unit had a single class number, as allocated to the driving motor car. Whereas within most ranges class numbers were allocated sequentially as new types were constructed, the Southern  Region adopted a more complicated system for their electric multiple units, with the second and third digits indicating in more detail the type of unit. Second digits were allocated as follows: Third digits were allocated as follows: Of course, many exceptions arose over time. One major change was to change the classification of unpowered trailer units from 49x numbers to 4x8 numbers (which involved reclassifying Class 491 to Class 438). When Southern Region unit numbers were changed to fit with the TOPS classification system, former 4x0 classes were all reclassified to 4x2. This was necessary because Southern Region units only  displayed the last four digits of their six-digit TOPS number, and it was decided that no painted unit number should commence with a '0'. It is worth noting that despite only showing the last four digits, the actual number of the unit was still the six-digit TOPS number. This often causes confusion both to enthusiasts and those outside the field alike. 2011 numbering and classification alterations and extensions - TOPS. In September 2011, the UK Rail Safety and Standards Board issued Railway Group Standard GM/RT2453,<ref name="RGS GM/RT2453"></ref> which made some alterations to the TOPS classes allocated  to various types of locomotive and multiple unit - primarily extending the number ranges for certain types of locomotives and multiple units where the previous allocation ranges were becoming exhausted. The standard also provided for the allocation of European Vehicle Numbers to most mainline rail vehicles in Britain, as part of the implementation of EC Directive 2008/57/EC (the Railway Interoperability Directive). Railway Group Standard GM/RT2453 was replaced in December 2017 by Rail Industry Standard RIS-2453-RST, which introduced the requirement for all new rail vehicles receiving authorisation to enter service in Britain after 1 January 2018 to display their  full 12-digit European Vehicle Number regardless of whether or not the vehicle is intended for use only on domestic services. Following the introduction of Standard RIS-2453-RST the allocation ranges have been as follows: Locomotives. Multiple units and fixed formation sets. Allocations made prior to the introduction of the GM/RT2453 standard were not changed. See also. For further information on individual classes of locomotive or multiple unit, see these pages: Related pages on BR numbering and classification include: