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LMS locomotive numbering and classification
LMS locomotive numbering and classification
LMS locomotive numbering and classification
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A number of different numbering and classification schemes were used for the locomotives owned by the London, Midland and Scottish Railway (LMS) and its constituent companies.

The LMS, formed on 1 January 1923 from many smaller companies included the Caledonian Railway (CR), Furness Railway (FR), Glasgow and South Western Railway (GSWR), Highland Railway (HR), Lancashire and Yorkshire Railway (LYR), London and North Western Railway (LNWR), Maryport and Carlisle Railway (MCR), Midland Railway (MR), North London Railway (NLR) and North Staffordshire Railway (NSR) as well as the minor Cleator and Workington Junction Railway (C&WJR), Glasgow and Paisley Joint Railway (G&PJR), Knott End Railway (KER), Stratford-upon-Avon and Midland Junction Railway (S&MJR), and Wirral Railway (WR) and from October 1936 the Somerset and Dorset Joint Railway (S&DJR)

For information about individual classes and locomotives, see Locomotives of the London, Midland and Scottish Railway.

Preceding schemes

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London and North Western Railway

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The LNWR inherited its numbering system from one of its constituents, the Grand Junction Railway. Locomotives were numbered in a series commencing at 1. No gaps were allowed in the series, so a new locomotive would either be numbered at the end of the series or would reuse the number of an older locomotive.

Older locomotives would then be either withdrawn or renumbered into the 'duplicate list' series used for those no longer in capital stock but which not yet completely life expired. These engines were numbered in various series over time: initially they took an 'A' suffix to the original number, then from 1862 they were renumbered above 1100, from 1870 above 1800, and from 1886 in the 3xxx series.

The GJR and LNWR also named their passenger tender locomotives (all locomotives were named until 1858), and often the same name and number combinations would be applied to new locomotives as they replaced older ones. The removal of names attached to freight engines after 1863 allowed them to be re-applied to the increasing stock of passenger engines, including those running on the former London and Birmingham Railway area of the LNWR, where locomotives had not been named.

Midland Railway

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The MR undertook a wholesale renumbering of its locomotive stock in 1907 based on usage, wheel arrangement, power classification (see classification section below), and age, with locomotives of the same class numbered together. The least powerful and oldest classes took the lowest numbers and locomotives were renumbered in order of age.

When the London, Tilbury and Southend Railway (LTSR) was absorbed by the MR in 1912, its locomotives were renumbered into this scheme. It had only two tender engines, both 0-6-0 types, and these became 2898 and 2899. The rest were tank locomotives of varying wheel arrangements, which required the adoption of new number ranges at the end of the tank engine series. In all, the number ranges used by the MR were as follows:

Number range Wheel arrangement Power classification
1–1197 Passenger tender engines
1–299 2-4-0 1
300–599 4-4-0 1 and 2
600–699 4-2-2 1 and 2
700–779 4-4-0 3
990–1197 4-4-0 4
1198–2199 Tank engines
1198–1199 4-4-0 (Passenger) Not classified
1200–1499 0-4-4T (Passenger) 1
1500–1599 0-4-0 (Freight) 0
1600–1999 0-6-0 (Freight) 1 and 3
2000–2099 0-6-4 (Passenger) 3
2100–2109 4-6-4 (Passenger) Ex-LTSR
2110–2179 4-4-2 (Passenger) Ex-LTSR
2180–2199 0-6-2 (Freight) Ex-LTSR
2200 onwards Freight tender engines
2200–2239 2-6-0 2
2290 0-10-0 Not classified
2300–2899 0-6-0 (Double framed) 1 and 2
2900 onwards 0-6-0 (Single framed) 1 to 4

While the majority of ex-MR locomotives were left unrenumbered by the LMS at Grouping in 1923, the ex-LTSR locomotives were subject to several renumberings to clear space for new stock, which changed the number ranges set out above.

Post-grouping numbering

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Shortly after the LMS was formed in 1923, it developed a new numbering scheme for all the locomotives that it had inherited. The scheme dealt with two key problems faced by the new company:

  • There were many locomotives with the same number, as each of the constituent companies had used a series starting at number 1
  • Many of the constituent companies had numbered their locomotives in a somewhat random way, and the renumbering allowed for all locomotives in the same class to be given consecutive numbers and similar classes to be numbered in blocks

These advantages more than overcame the disadvantage of the effort involved in renumbering almost every locomotive and giving them a number that usually bore no relation to its pre-Grouping identity, except for the Midland Railway locomotives that had been renumbered along similar lines in 1907 and mostly retained their numbers.

The system comprised four groups of numbers into which locomotives from a set of railways were numbered:

Number range Original owning company
1–4999 Midland Railway (including the London, Tilbury and Southend Railway, absorbed in 1912), North Staffordshire Railway and Stratford-upon-Avon and Midland Junction Railway
5000–9999 London and North Western Railway (including the North London Railway) and Wirral Railway
10000–12999 Lancashire and Yorkshire Railway, Furness Railway, Maryport and Carlisle Railway, Cleator and Workington Junction Railway and Knott End Railway
14000–17999 Caledonian Railway, Glasgow and South Western Railway, Highland Railway and Glasgow and Paisley Joint Railway

Within each group, locomotives were numbered in blocks which ran (low to high numbers) as set out below. Within each block, the least powerful locomotives took the lowest numbers.

Block description MR etc. numbers LNWR etc. numbers LYR etc. numbers Scottish numbers
Passenger tender locomotives 1–1199 5000–6399 10000–10599 14xxx
Passenger tank locomotives 1200–1499 / 2000–2219 6400–6999 10600–11199 15xxx
Freight tank locomotives 1500–1999 / 2220–2289 7xxx 11200–11999 16xxx
Freight tender locomotives 2290–4999 8xxx-9xxx 12xxx 17xxx

When the Somerset and Dorset Joint Railway locomotives were absorbed in 1930, they were mostly allocated numbers in the Midland Railway series (appropriate, since the SDJR had been jointly owned by the Midland Railway and many MR designs had been used on the SDJR), though some took numbers in the former LNWR series.

New-build LMS locomotives were not allocated any particular numbers, but were fitted into the most appropriate division. The unallocated 13xxx series of numbers were also used for new build LMS types.

1932 renumbering

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In 1932, as older locomotives had been withdrawn and new standard LMS designs were becoming more common, it was decided that modifications should be made to the numbering system. In short, all LMS-built locomotives were to have numbers in the 1–9999 series, with pre-Grouping locomotives being renumbered out of that series as required to accommodate them.

The introduction of this scheme involved renumbering both new and old locomotives to put them in the appropriate sequences. During the remainder of the 1930s, numbers were cleared for new locomotives by simply adding 20000 to the numbers of old locomotives.

Diesel shunters, which started to appear from the early 1930s onwards, were numbered in the same series as steam locomotives. Originally a series commencing at 7400 was planned, but it was soon evident that this would not provide sufficient space and it was replaced by a series commencing at 7050. The prototype mainline diesel locomotives, the first of which was introduced at the end of 1947 just prior to Nationalisation were given the 'significant numbers' 10000 and 10001.

Application by British Railways

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New engines built by British Railways to ex-LMS designs after Nationalisation in 1948 continued to use this numbering system, albeit with 40000 added to the numbers to avoid number conflicts with other absorbed engines (see BR locomotive and multiple unit numbering and classification). There were some minor amendments made by BR, however:

  • Former LMS diesel locomotives were numbered in the 10xxx series (mainline locomotives) and 12xxx series (shunters).
  • Locomotives numbered above 20000 by the LMS were renumbered into the 58xxx series, in order to avoid number conflicts with ex-LNER locomotives.

Classification

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LMS system

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The Midland Railway introduced a system of locomotive classification based on the power output represented by a locomotive's tractive effort at 50 mph (passenger locomotives) or 25 mph (goods locomotives). This is the continuous tractive effort and is much lower than the starting tractive effort which is the figure usually quoted in technical publications.

This system was adopted by the LMS and also, from 1948 the nationalised British Railways. The classification was made up of a number (representing the power output - 0 being low power and 9 high power) and a letter (representing the type of work the locomotive was intended for), e.g. 4F. Over the years there were some modifications to the system, but the basics remained the same.

The principal downside with this method of classification was that it did not distinguish between particular classes of locomotive, so many very different types would have been classified '4F' for instance.

Power class Minimum and maximum tractive effort (lbf)
Passenger locos at 50 mph Freight locos at 25 mph
0 Under 3,360 (used from 1928) Under 6,385 (used from 1928)
1 3,360–4,479 6,385–8,064
2 4,480–5,599 8,065–9,744
3 5,600–6,719 9,745–11,424
4 6,720–7,839 11,425–13,104
5 7,840–8,959 13,105–14,784
6 8,960–10,079 14,785–16,464
7 10,080–11,199 16,465–18,144
8 11,200 and over 18,145 and over (used from 1937)
9 Not allocated Used by British Railways from 1954
F
Freight (from 1928)
G
Goods (until 1928)
MT
Mixed traffic (freight and passenger)
P
Passenger
XP
Enhanced passenger (higher end of power range)

A single number without a suffix letter was originally used by the LMS on locomotives that were not of Midland Railway origin until 1928. Thereafter, it was used to indicate a mixed traffic locomotive. Where a mixed traffic locomotive fell into different power ranges, dual classification was used, e.g. 5P4F. From 1953 until 1957 (but remaining painted on locomotives until much later), the suffixes 'FA' and 'FB' were sometimes used to distinguish between freight locos with different load limits due to their braking characteristics on unfitted goods trains.

Notes

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

LMS locomotive numbering and classification

View on Grokipedia
from Grokipedia
The London, Midland and Scottish Railway (LMS), established on 1 January 1923 through the amalgamation of several pre-existing companies including the London and North Western Railway, , and , inherited approximately 10,316 steam locomotives across 393 distinct types, necessitating a unified numbering and classification system to standardize . This system initially allocated blocks of numbers to locomotives based on their originating companies, with renumbering efforts commencing in 1924 and completing by 1928 to integrate the diverse inherited stock into a cohesive scheme. Complementing the numbering, the LMS introduced a power classification scheme around 1924, dividing locomotives into eight classes (1 through 8) primarily based on tractive effort calculations—typically at 50 mph for passenger engines and 25 mph for freight types—along with boiler capacity and intended duties, denoted by suffixes such as P for passenger, F for freight, and M for mixed traffic. For instance, express passenger locomotives like the Class 6 Royal Scots were assigned higher classifications reflecting their superior power output, while goods engines such as the Class 7 0-8-0s were tailored for heavy freight hauling. Over the LMS era (1923–1948), the system evolved to support , reducing the number of locomotive classes from 393 to 230 by and focusing new construction on just 14 principal types under chief mechanical engineers like Henry Fowler and . A significant renumbering further rationalized the fleet by reallocating numbers to prioritize newer designs and withdraw obsolete ones, ensuring efficient allocation across the network. This framework not only facilitated operations but also influenced post-nationalization British Railways practices, where the LMS classification was largely adopted for .

Pre-Grouping Numbering Schemes

London and North Western Railway

The (LNWR), the largest constituent of the London, Midland and Scottish Railway (LMS), inherited a sequential numbering system from the Grand Junction Railway, commencing at No. 1 with no initial gaps in allocation. This approach originated in the , with early such as the Bury-designed 2-2-0s (Nos. 1–36 and 49–52) and 0-4-0s (Nos. 61–90) built between 1837 and 1841, emphasizing a straightforward, gap-free progression for identification across the growing fleet. By the mid-19th century, the system supported the LNWR's expansion, with examples including the first Wolverton-built as No. 92 in 1845–1846 and early passenger engines spanning Nos. 1–256. The absorption of smaller lines in 1846, such as the Trent Valley Railway (adding Nos. 147–171 in 1846–1847), introduced the first duplicates, necessitating suffixes like "A" for older locomotives to distinguish them from new builds. This evolved in the with a dedicated duplicate series of 1100–1799 for reassigned older stock, followed by the 1800–2599 series in the 1870s to accommodate further growth and avoid conflicts during rebuilds and transfers, such as Southern Division extensions (Nos. 320–344). A major reorganization in allocated the 3000 series for new constructions, while older locomotives were renumbered into the 2000–2999 range or higher to eliminate overlaps, reflecting the fleet's scale amid ongoing expansions.[](Baxter, David (ed.). British Locomotive Catalogue 1825–1923, Volume 2A: London and North Western Railway and its constituent companies (1980). Moorland Publishing.) Naming practices complemented numbering until the late 19th century, with all passenger locomotives bearing names until 1858, such as "Sefton" (No. 320) and those exhibited like No. 373 at the 1862 International Exhibition. Freight locomotives retained names briefly post-1863 but were increasingly identified by numbers alone, phasing out names for operational efficiency; examples include the goods engine "Queen" (No. 1171). Between 1906 and 1912, absorbed stock from joint lines like the Caledonian Joint was renumbered into existing series, contributing to a fleet exceeding 2,800 locomotives by 1922, all without comprehensive class prefixes.[](C. Williams, A register of all the locomotives now in use on the London & North Western Railway (Crewe, 1912).) This expansive, numerically driven system influenced the LMS's initial 1923 allocation blocks, such as 5000–9999 for ex-LNWR stock.[](Baxter, David (ed.). British Locomotive Catalogue 1825–1923, Volume 2B: London and North Western Railway and its constituent companies (1979). Moorland Publishing.)

Midland Railway

Prior to 1907, the 's locomotive numbering was disorganized, resulting from multiple mergers and acquisitions that led to duplicate and inconsistent allocations across its fleet. This chaos prompted a major renumbering scheme in 1907, implemented under the direction of Locomotive Superintendent Richard Deeley, which systematically organized the approximately 1,800 locomotives based on their primary usage (, mixed traffic, or goods), tender type, , and an early power classification system graded from 0 to 9. The scheme aimed to streamline maintenance, allocation, and identification, reflecting the company's emphasis on and efficiency in operations. The 1907 renumbering divided the fleet into broad blocks by duty and tender configuration, with further subdivision by and power within those blocks. Passenger tender engines occupied numbers 1–1197, encompassing classes such as 2-4-0s (1–299), 4-4-0s (300–599 and 4000–4199 for larger variants), and compounds (1000–1099). Mixed-traffic tender engines were assigned 1200–1699, primarily s and 4-4-0s for versatile duties. Goods tender engines received 2000–2599 for s and similar types, while engines for shunting and local services filled 2600–2897 and higher ranges like 3000–3999 for T. Specific examples include 2600–2699 for standard goods locomotives and 2700–2799 for superheated variants, integrating s to facilitate quick recognition of capabilities.
Number RangeUsage and Wheel ArrangementPower Grade ExamplesNotes
1–1197Passenger tender engines (e.g., , )0–3Subdivided by class; e.g., 300–599 for s
1200–1699Mixed-traffic tender engines (e.g., , )1–3Versatile classes for passenger/goods
2000–2599Goods tender engines (e.g., )2–4Heavy freight focus
2600–2699Goods tank engines (T)1–2Shunting and short-haul
4000–4199Passenger tender engines2–3Larger express types
Following the 1907 scheme, the ceased naming new locomotives, relying solely on numerical classification augmented by power grades to denote tractive effort and suitability. The highest numbers were reserved for absorbed stock; in 1912, upon acquisition of the London, Tilbury and Southend Railway, its two surviving locomotives were renumbered 2898–2899, fitting into the tank engine block without disrupting the established structure. This system provided a logical foundation that influenced the London, Midland and Scottish Railway's initial 1923 passenger engine allocations.

Lancashire and Yorkshire Railway

The (L&YR) utilized a sequential numbering system for its locomotives, commencing from No. 1 without gaps in the initial years following its formation in , to accommodate the rapid expansion of its fleet serving the industrial heartlands of . As the railway grew, numbering proceeded sequentially for new builds, with later locomotives assigned progressively higher numbers, while class designations—often lettered after designers or types—facilitated identification within the predominantly freight-oriented stock. For instance, the Aspinall "A" class 0-6-0 goods engines, introduced in 1889, were allocated numbers in the 1000–1129 range for early batches, emphasizing their role in heavy haulage across Lancashire's mills and mines. Similarly, the earlier Bury types, classified as "B" class 0-4-0s, occupied low numbers such as 13–14 and 47–52, many of which were rebuilt for continued service in shunting duties. Absorptions of smaller constituent lines were managed by assigning distinct numerical blocks to integrated stock, preventing overlaps with existing L&YR numbers and preserving traceability. The 1859 amalgamation with the , for example, saw that company's locomotives—originally numbered 1–63—renumbered by adding 600, resulting in the 601–663 series to distinguish them from core L&YR builds. Later expansions employed similar block allocations, such as the 1000 series for subsequent tender engine constructions, ensuring orderly management of the diverse fleet amid ongoing industrial demands. This system reflected the L&YR's pragmatic approach to fleet administration, prioritizing functionality over complex categorization. By 1922, the L&YR operated over 1,600 locomotives, with numbers extending beyond 1800 for tender types and engines post-1900 often placed in elevated series to separate them from mainline stock. Naming conventions were restricted largely to select early passenger classes, such as the 4-4-0 "Queen" engines, underscoring the railway's numerical focus for the bulk of its shunting and freight locomotives that powered Lancashire's and industries. Notable examples include John Aspinall's 2-4-2T passenger , constructed from 1889 to 1911 and numbered 10800–11129, which exemplified the shift to higher ranges for specialized suburban services. George Hughes' rebuilds, spanning 1914–1922, incorporated and other improvements to existing classes, with affected locomotives reassigned to the 12000 series to denote their enhanced configuration. Upon the formation of the London, Midland and Scottish Railway in 1923, surviving L&YR locomotives were transferred within the dedicated block of 10000–12999.

Scottish Constituent Railways

The Scottish constituent railways of the London, Midland and Scottish Railway (LMS)—namely the , , and —operated relatively small locomotive fleets tailored to regional services in , with numbering schemes that emphasized sequential allocation and class designations to manage limited stock efficiently. These practices reflected the compact networks and specialized traffic, such as passenger services to the Highlands or freight along the Clyde, contrasting with the larger, more industrialized English constituents. Duplicates were minimized through careful assignment, and absorbed locomotives from smaller lines were integrated into higher number blocks. The Caledonian Railway employed a sequential numbering system from 1 to 919 by 1922, assigning numbers upon entry into service and grouping locomotives by class based on the number of the first member to enter . For instance, the 49 Class 4-6-0 locomotives were numbered 264–271, while the 903 Class comprised numbers 903–907. Duplicates were rare, and stock absorbed from other companies was typically added to higher ranges, such as the 800-series for goods engines. A key example is the 1899 McIntosh 812 Class , built at St. Rollox works and numbered 812–831, which featured improved braking for mixed . The numbered its locomotives from 1 to 541, with gaps arising from withdrawals of older stock, necessitating occasional renumbering to consolidate active engines. Class designations were prefixed numerically, as seen in the 403 Class 2-6-0 freight locomotives numbered 401–410 and the Drummond 0-6-2T tanks numbered 150–167 for suburban duties. Builds at the works were allocated in consecutive blocks to streamline production and maintenance. In 1922, the Cardean 4-6-0 express engines were constructed but received LMS prefixes as 15470–15479 upon grouping. The maintained a small fleet numbered sequentially from 1 to 199, incorporating class letters for identification alongside numbers, which suited its sparse, mountainous routes. Examples include the "C" Class 4-4-0 passenger engines numbered 99–102 and the Jones 4-6-0 numbered 103–112. Post-1900, locomotives built at Lochgorm Works filled numbering gaps from earlier retirements. Between 1915 and 1920, the Clan 4-6-0 class was introduced as numbers 49–58 for mainline services. Joint lines, such as the Glasgow and Paisley Joint Railway, utilized shared numbering conventions, with their locomotives (e.g., Nos. 1 and 2) incorporated into CR or GSWR blocks upon absorption around 1913. Upon LMS formation in , these Scottish fleets were consolidated into the 14000–14999 block to preserve regional identities.

Post-Grouping Numbering Schemes

1923 Initial Allocation

The London, Midland and Scottish Railway (LMS) was formed on 1 January under the terms of the , which amalgamated several pre-existing companies into four major groupings. This new entity inherited 10,316 from its constituent companies, encompassing a diverse array of designs and numbering practices that required immediate rationalization to avoid conflicts across the unified system. The initial , implemented from the outset of operations, assigned broad blocks of numbers to locomotives based on their originating company, preserving as much as possible the pre-grouping identities while ensuring uniqueness within the LMS fleet. The allocation of number blocks was structured as follows: numbers 1–4999 were reserved for locomotives from the (MR), including those previously absorbed from the London, Tilbury and Southend Railway and the (NSR); 5000–9999 for engines from the London and North Western Railway (LNWR), (NLR), and Wirral Railway (WR); 10000–12999 for the (L&YR) and (FR); 14000–17999 for Scottish constituents such as the Caledonian Railway (CR), (G&SWR), (HR), and Glasgow and Paisley Joint Railway; Within these blocks, sub-organization generally followed the originating company's conventions by locomotive type—for instance, MR passenger tender engines occupied 1–1199 and goods types 2000–2999, while LNWR allocations mirrored its pre-1923 passenger and freight divisions to minimize disruption. New locomotives built by the LMS after formation were assigned the lowest available numbers within the overall scheme, with early prototypes and experimental types often placed in the 16000 series to avoid overlapping inherited stock. The scheme was applied retrospectively to all inherited stock effective from the grouping date, with only minor adjustments made later, such as the 1930 absorption of the (S&DJR) locomotives into the 9600–9699 range.

1933 Renumbering

In 1932, the London, Midland and Scottish Railway (LMS) initiated a major renumbering scheme as withdrawals of older pre-Grouping locomotives created opportunities to prioritize lower numbers for its new standard designs, reflecting a shift toward unification and modernization under Chief Mechanical Engineer . This addressed the growing proportion of LMS-built locomotives, allowing them to occupy the 1–9999 range while reassigning surviving pre-Grouping stock to higher numbers starting at 20000. The scheme built on the initial 1923 allocation by further consolidating blocks to favor contemporary classes, with over 5,000 locomotives affected across the system. For instance, Stanier-designed locomotives, such as the Class 5 4-6-0 "Black Fives," were allocated numbers from 5000 onward starting in 1934, while earlier LMS standards like the Fowler 2-6-2T tanks moved from 15500–15569 to 1–70 in 1934. Pre-Grouping examples included ex-Midland Railway locomotives renumbered from their original blocks to 20001 and above, and ex-LNWR "Precursor" 4-6-0s having 20000 added to their existing LMS numbers in 1934. Implementation began in 1933 with key passenger and mixed-traffic classes, progressing through the decade to achieve full unification by 1935. Diesel locomotives, introduced around this period, were initially numbered from 7050, such as the Armstrong Whitworth 350 hp shunters (7059–7068), with later prototypes reassigned to the 15000 series. Specific adjustments for joint lines included the Somerset and Dorset Joint Railway (S&DJR) stock, which had been numbered 9600–9680 in 1930, being shifted to 13000–13810 by 1932. Departmental stock was allocated to the 18000 series to avoid conflicts with running numbers. The following table summarizes major block shifts under the scheme, using representative classes:
Original Block (Pre-1932)New Block (Post-Renumbering)Example ClassYear Completed
13000–132442700–2944Hughes/Fowler "Crab" 2-6-01933
9600–9680 (S&DJR)13000–13810S&DJR 0-6-0T1932
Various (ex-/LNWR)20000+ Compounds, LNWR Precursors1934
15500–155691–70Fowler 2-6-2T1934
N/A (new builds)5000–5999Stanier Class 5 4-6-01934–1935
Exceptions preserved certain identities: named locomotives retained their names alongside new numbers. Key milestones included the 1933 start for main passenger classes like the followed by freight and shunting types in 1934, culminating in system-wide completion by 1935.

British Railways Continuation

Upon the vesting of the London, Midland and Scottish Railway (LMS) into British Railways (BR) on 1 January 1948, the numbering of ex-LMS steam locomotives was adapted by adding 40,000 to their existing LMS numbers to create a unified national system. For example, LMS Coronation Class Pacific No. 6201 became BR No. 46201. Exceptions applied to LMS locomotives already numbered above 20,000, which were reassigned to the 58,000 series to prevent overlap with ex-London and North Eastern Railway (LNER) locomotives prefixed with 60,000. This adaptation built upon the LMS's 1933 renumbering scheme as a foundational framework. By the end of 1947, the LMS stock list included approximately 7,000 locomotives, many of which underwent minor adjustments during the transition due to ongoing withdrawals and reallocations for mixed-traffic duties. For instance, a notable example of subsidiary stock handling is the (S&DJR) No. 88, which carried LMS No. 13,808 before becoming BR No. 53,808. Ex-LMS Class 5 4-6-0s were numbered in the 4xxxx series (e.g., adding 40000). Ex-LMS diesel locomotives were incorporated into BR's early diesel numbering, with mainline examples assigned to the series and shunters to the 12,000 series. Key prototypes from this era included the 1947-1948-built LMS Twins Nos. and 10,001. New BR diesel locomotives introduced from 1957 onward adopted the Dxxxx prefix, serving as a precursor to the Total Operations Processing System () implemented from 1973.

Locomotive Classification

Pre-Grouping Systems

Before the formation of the London, Midland and Scottish Railway in 1923, its constituent companies maintained disparate locomotive classification systems tailored to their individual operations, with no overarching across the network. These schemes generally emphasized wheel arrangements, designer influences, or service roles rather than uniform power metrics, reflecting the era's fragmented railway landscape. The London and North Western Railway adopted an informal approach to classification, grouping locomotives by size, type, and designer without a numerical power scale. Designs by Francis Webb, such as the compounds, often received letter designations like the A Class goods engines or D Class freight locomotives, prioritizing practical utility over quantified performance. In contrast, the developed one of the more structured pre-grouping systems, assigning early power grades from 0 to 5 based on prior to 1907. Following the 1907 renumbering under Richard Deeley, these grades were incorporated into class identifiers, as seen in the 3F rating for the 1000 Class goods engines used in banking and freight duties. The relied on letter-based classes named after chief mechanical engineers, separating freight and passenger engines without formalized power measurements. John Aspinall's A Class consisted of goods locomotives (later expanded as Class 27), while George Hughes introduced superheated variants like the H Class for enhanced freight performance. Scottish constituent companies exhibited similar diversity in their classifications. The Caledonian Railway used letter designations for its main classes, including the express passenger engines of the series, designed by J.F. McIntosh for high-speed services on key routes. The applied a numerical scheme denoting type and relative power from 1 to 5, with Class 1 covering basic shunters and Class 5 encompassing robust freight locomotives like the Drummond 403 Class "Austrian Goods." Meanwhile, the organized its fleet into letter classes A through K, aligned with wheel arrangements and power suitability for challenging terrain; for instance, the A Class handled passenger duties, while later entries like the addressed mixed-traffic needs. Across these pre-grouping systems, a shared convention involved suffixes to indicate variants, such as T for engines adapted from tender designs. Tractive effort was rarely standardized until the Midland Railway's methods gained broader influence, setting a precedent for post-grouping unification.

LMS Power Classification

The London, Midland and Scottish Railway (LMS) adopted a unified power classification system in 1925, extending the pre-grouping Midland Railway's numerical scale from 0 to 8 based on a locomotive's calculated at 50 mph for passenger engines and 25 mph for freight types. This approach aimed to standardize the assessment of locomotive capabilities across the diverse inherited fleets, facilitating efficient allocation to duties. The (TE) for simple expansion locomotives was determined using the formula TE = (cylinder area × boiler pressure × 0.85) / 100, with adjustments applied for compound expansion engines to account for their mechanical advantages. Classifications combined a number indicating relative power with a letter denoting primary use: 'P' for locomotives optimized for speed and , 'F' for freight locomotives emphasizing sustained hauling power, and dual-purpose designations like 5P4F for mixed-traffic engines capable of both roles. The numerical grades corresponded to approximate thresholds, such as class 0 for under 7,000 lbf (suitable for light shunting) and class 8 for over 30,000 lbf (for heavy express or mineral trains). This system built briefly on the Midland Railway's earlier -based grading but expanded it to accommodate larger post-grouping designs. Refinements in the 1930s, particularly under Chief Mechanical Engineer , incorporated evolving design priorities, with the Jubilee class (4-6-0) rated 6P for its balanced express performance and the Coronation class () as 7P for high-speed mainline services. Tank engine variants received a 'T' to distinguish their self-contained operation, such as 2P-T for suburban tanks. From 1932 onward, classifications were prominently painted on cab sides following the major renumbering scheme, enabling quick identification in depots and on the line; by 1947, around 150 distinct classes had been assigned grades under the system. Significant milestones included the 1925 formal introduction amid standardization efforts and periodic wartime reviews between 1943 and 1948 to address maintenance and utilization under resource constraints. A representative example is the LMS Fowler 4F 0-6-0 goods engine, classified as 4F within the LMS framework to reflect its performance in freight duties.

References

  1. http://www.lyrs.org.uk/images/uploads/Paper_-_Cox_1946_-_I.Loco.E_-_A_Modern_Loco_History%2C_LMS_1923_to_1932.pdf
  2. https://www.lmssociety.org.uk/topics/unification.shtml
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  4. https://www.nsrsg.org.uk/LNWRChronology.php
  5. https://lyrs.org.uk/locomotives/
  6. https://steamindex.com/locotype/lyr.htm
  7. https://lyrs.org.uk/the-railway/
  8. https://preservedbritishsteamlocomotives.com/2p-between-50621-50899-10897-2-4-2t-lyr-aspinall-class-5/
  9. https://steamindex.com/locotype/caleloco.htm
  10. https://steamindex.com/locotype/gswrloco.htm
  11. https://steamindex.com/locotype/highland.htm
  12. https://steamindex.com/books.htm#macleod
  13. https://www.lmssociety.org.uk/assets/pdfs/LMSSocietyTeachIn1976.pdf
  14. https://preservedbritishsteamlocomotives.com/53808-sdjr-88-lms-9678-lms-13808-br-53808/
  15. https://preservedbritishsteamlocomotives.com/5mt-42700-42944-2-6-0-lms-hughes-fowler-horwich-crab/
  16. https://chasewaterstuff.wordpress.com/category/steam-locomotive-classes-of-a-leisurely-era/page/11/
  17. https://train.spottingworld.com/LMS_Fowler_2-6-2T
  18. https://www.derbysulzers.com/derby1010.html
  19. https://www.3smr.co.uk/wheelslms.html
  20. https://collection.sciencemuseumgroup.org.uk/objects/co8088759/re-numbering-of-ex-lms-locomotives
  21. https://www.brdatabase.info/locoqry.php?action=locodata&id=LMS6201&type=S&loco=6201
  22. https://www.ianrathbonemodelpainting.co.uk/british-railways-liveries.php
  23. https://www.newcomen.com/steam-locomotives-of-british-railways/
  24. https://www.svrwiki.com/Locomotive_numbering
  25. http://www.railfaneurope.net/misc/gbnum.html
  26. https://steamindex.com/locotype/midland.htm
  27. https://steamindex.com/locotype/aspinall.htm
  28. https://steamindex.com/locotype/stanloco.htm
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