British Rail Class 37 – English Electric's Legendary Type 3 Diesel Workhorse

Historical Background and Context

The story of the BR Class 37 begins not in Britain, but in East Africa. English Electric had achieved remarkable success supplying robust diesel locomotives to East African Railways, where they achieved an impressive 93% availability rate in extreme conditions. This proven design featured a 2,024 hp diesel engine producing 1,840 hp when working at 9,000 feet above sea level, demonstrating the fundamental soundness of the engine, generator, traction motors, and control gear.

When the British Transport Commission published the BR Modernisation Plan in December 1954, it called for massive investment of £1.2 billion to replace all steam traction with diesel and electric locomotives. The plan identified a need for Type 3 locomotives with power output between 1,500 hp and 1,999 hp for mixed-traffic operations. English Electric responded by offering their proven African design with a de-rated engine producing 1,750 hp at rail—powerful enough for heavy freight yet suitable for secondary passenger services.

The 1,750 hp rating was deliberately conservative, ensuring reliability and longevity. This power output placed one Type 3 as equivalent to one Stanier Black Five steam locomotive, making it ideal for replacing steam on mixed-traffic duties. The low gearing suited both freight work and passenger trains on secondary routes, whilst the moderate power rating meant the engine wasn't highly stressed, contributing to the class's legendary reliability.

Remarkably, English Electric was so confident in their African design that they proceeded directly to production without building a prototype—an audacious decision that proved entirely justified. British Railways placed the first order for 42 locomotives in January 1959, with D6700 delivered in November 1960 and entering service on 2 December 1960 at Stratford depot. Production continued through seven separate orders until D6608, the final locomotive, was delivered on 9 November 1965.

Manufacturing was split between two facilities to meet BR's urgent need for steam replacement: Vulcan Foundry at Newton-le-Willows, Lancashire (the primary facility) and Robert Stephenson & Hawthorns at Darlington. The total build of 309 locomotives was originally numbered D6700–D6999 and D6600–D6608, before TOPS renumbering in 1973 created the 37001–37308 series we recognise today.

Compared to competing Type 3 designs like the Brush Type 2 (Class 31), the English Electric Type 3 proved vastly superior. The Class 31, with only 1,250 hp originally (later 1,470 hp after re-engining) and an A1A-A1A wheel arrangement, suffered from unreliable Mirrlees engines requiring expensive replacement. The BR Class 37's all-axle Co-Co configuration, higher power output, and proven engine design made it the clear winner, ultimately becoming the standard Type 3 when other types were withdrawn in the 1980s.

Design and Technical Specifications

At the heart of every BR Class 37 lies the English Electric 12CSVT diesel engine—a 12-cylinder V-type powerplant with 10-inch bore and 12-inch stroke. The designation CSV denotes its key features: C for intercooler, S for supercharger/turbocharger, and V for V-configuration. Running at 750-900 rpm, this turbocharged and intercooled engine produced a reliable 1,750 bhp (1,305 kW), delivering approximately 1,250 hp at the rail.

The electrical system originally comprised an English Electric EE822/10G main generator and EE911/5C auxiliary generator, both DC units, feeding power to six English Electric 538/1A nose-suspended DC traction motors—one per axle in the Co-Co arrangement. Later refurbished locomotives (37/4, 37/5, 37/6, 37/7 subclasses) received Brush alternators instead, improving reliability and efficiency for modern service.

The Co-Co wheel arrangement proved crucial to the Class 37's versatility. With all six axles powered across two three-axle bogies, the locomotive distributed its weight evenly whilst providing excellent adhesion for both starting heavy freight trains and maintaining speed on passenger services. The CP7 cast-frame bogies were interchangeable with Class 50 and Class 55 Deltic locomotives, and featured the same basic design—so much so that fittings for Deltic cab steps are visible on Class 37 bogies.

The distinctive bodyside grilles became an iconic recognition feature of the BR Class 37, providing adequate cooling for the 12CSVT engine in all conditions. The utilitarian 1960s design featured a strong family resemblance to other English Electric designs like the Class 40 and Class 23 Baby Deltic, with symmetrical stepped driving compartments at each end and prominent rectangular doors along the locomotive sides for cabin access.

Early builds featured split headcode boxes (two square boxes containing four digits total) with nose-end connecting doors designed to allow crew exchange whilst in motion. From D6819 onwards, a single centrally-placed headcode panel replaced the split arrangement, nose-end doors were eliminated, and horns moved from body mounting to roof mounting. These variations provide excellent period-specific detail opportunities for modellers.

The relatively low axle loading for size and power made the BR Class 37 invaluable for lines with weight restrictions, becoming the only mainline locomotive type available in significant numbers for such routes. This Route Availability 5 classification meant Class 37s could operate on lightly-laid branch lines where heavier locomotives couldn't venture—a key factor in their long operational life and continued utility into the 21st century.

Service History and Operations

The BR Class 37 entered service in December 1960 with initial allocations focused on the Eastern Region. Stratford depot received D6700–D6704, D6709–D6720, and D6725–D6729, immediately putting them to work on passenger services from Liverpool Street to Norwich, Cambridge, Harwich International, and Clacton-on-Sea. The first passenger use came on 6 January 1961 when D6700 substituted for a failed Class 31 on The Fenman, with regular services commencing on 9 January 1961. These locomotives maintained an exclusive preserve on Harwich International boat trains for over 20 years.

The North Eastern Region received substantial allocations with Thornaby operating 50 locomotives—one of the largest single depot allocations. Hull Dairycoates, Gateshead, and Sheffield Darnall/Tinsley depots operated Class 37s on a variety of freight and secondary passenger duties, including Pullman services to London King's Cross and Harwich boat trains via the Woodhead Tunnel route.

The Western Region's adoption of the Class 37 proved decisive to the design's success. Trial of D6742 and D6743 in late 1962 proved so successful that within two years, over 100 Class 37s were allocated to Western Region depots. Cardiff Canton received 51 locomotives whilst Landore, Swansea operated 47—the two largest depot allocations. These locomotives handled heavy coal and metals traffic in South Wales on short, steeply-graded branch lines to collieries like Tower, Coedbach, and Cwmbargoed, typically hauling 32-wagon rakes of 32-ton HAA hoppers in merry-go-round operation. From 1964, pairs of Class 37s replaced Hymeks on banking duties up the notorious Lickey Incline. Between 1965 and 1967, eighteen locomotives (D6875–D6892) were modified for 100 mph trials on Western Region express services.

The 1980s refurbishment programme at BR Engineering's Crewe Works transformed the Class 37 fleet and extended operational life by decades. Multiple specialist subclasses emerged from this programme. Class 37/4 locomotives received Electric Train Heating (ETH) equipment for passenger work, requiring replacement of DC generators with Brush alternators. Thirty-one locomotives were converted between 1985 and 1986 specifically for Scottish passenger services on the West Highland Line, Far North Line (Inverness-Thurso/Wick), and Kyle of Lochalsh line. These locomotives received ETH capacity sufficient for modern Mark 2 air-conditioned coaching stock, finally eliminating the need for intermediate ETHEL vehicles.

Class 37/5 received similar refurbishment to the 37/4 but without train heating equipment, designating them for freight-only use. Class 37/6 were modified for the aborted Nightstar Channel Tunnel sleeper services, with twelve locomotives converted with special coupling equipment for continental operations. Class 37/7 heavy freight variants received extra ballast increasing weight to 120 tons and modified gearing, with 44 built for intensive South Wales coal and steel traffic. Class 37/9 represented an experimental re-engineering programme testing alternative engines (Mirrlees MB275Tt and Ruston RK270Tt) for a proposed Class 38, though only six were built between 1986 and 1987 and all were withdrawn by 1999-2000.

Throughout their operational life, BR Class 37 locomotives worked notable services including Anglo-Scottish expresses, West Highland Line tourist trains, North Wales coast passenger services, Cambrian line trains to Aberystwyth, Heart of Wales line services (with specially fitted headlamps), and intensive coal, steel, and china clay freight operations. The transition through BR blue livery era, Railfreight sector identities (grey with red stripe, then triple grey sector logos for Coal, Metals, Petroleum, Distribution, and Construction), and privatisation saw the class adapted to each new operational requirement.

Fleet

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Withdrawal and Preservation Legacy

Withdrawals began tragically early when D6983 was destroyed in a December 1965 collision at Bridgend—the only Class 37 never to receive a TOPS number. However, systematic withdrawals didn't commence until the 1980s, accelerating dramatically through the 1990s and 2000s as the introduction of Class 66 locomotives from 1998 onwards displaced Class 37s from freight duties. EWS acquired 250 Class 66s, leading to mass withdrawals of older traction including the bulk of the Class 37 fleet.

Final regular passenger workings ended progressively: Cardiff-Rhymney services concluded in April 2005 with specially painted 37411 and 37425, whilst the Fort William Caledonian Sleeper—the last daily Scottish Class 37 passenger work—ended in June 2006 with replacement by Class 67 locomotives. Direct Rail Services announced retirement of its Class 37 fleet in 2024-2025, with replacement by Class 68 and Class 88 locomotives, marking the effective end of six decades of frontline commercial service.

Yet remarkably, approximately 60 BR Class 37 locomotives remain in mainline service as of 2025, testament to their robust design and continued utility. Current commercial operators include Colas Rail (7 operational locomotives handling rail head treatment trains and infrastructure work), Rail Operations Group (6 locomotives leased from Europhoenix for EMU movements), Network Rail (3 Class 97/3 conversions for ERTMS testing on the Cambrian Line), and various spot-hire companies. West Coast Railways maintains 11 locomotives (5-6 operational) for charter train operations, particularly on Scottish routes like the West Highland Line where their Route Availability 5 classification allows operation where heavier locomotives cannot venture.

Heritage railways operating Class 37s include Severn Valley Railway (37263, 37308), Great Central Railway (D6700, 37714), Keighley & Worth Valley Railway (37075, which appeared as Class 40 D326 in the BBC drama "The Great Train Robbery"), North Yorkshire Moors Railway (37264), Caledonian Railway (37097 "Old Fettercairn"), Bo'ness & Kinneil Railway (37175), and over fifteen other heritage lines. Several preserved locomotives maintain mainline certification for charter work, ensuring the distinctive "Tractor" sound continues to grace Britain's railways.

The engineering legacy of the BR Class 37 extends beyond preserved examples. The experimental Class 37/9 Mirrlees engine programme influenced the Class 60 design, whilst the successful 1980s refurbishment programme demonstrated the value of life-extension over new-build—a lesson applied to other locomotive classes. The low axle loading concept influenced later designs for restricted routes, and the ETH conversion model pioneered on 37/4s was subsequently applied to Classes 31/4 and 47/4.

Modelling Significance and Scale Replications

OO gauge modellers enjoy an embarrassment of riches when selecting BR Class 37 models. Three manufacturers currently offer comprehensive ranges with varying levels of detail, features, and pricing to suit every budget and requirement.

Bachmann Branchline launched their all-new Class 37 range in 2022, designed from scratch using original drawings and laser scans. This award-winning model features a five-pole twin-shaft motor with dual flywheels, all-wheel drive with electrical pickup from all twelve wheels, PLuX22 DCC decoder socket, and dual fitted speaker system on all models. Directional lighting includes high-intensity headlights, cab lighting, and engine room lighting (on DCC), plus 'Yard Light' mode for marker/tail lights. Standard DCC Ready models (catalogue numbers 35-301 through 35-338) retail at £169.50-£195.95, whilst Sound Fitted variants with Zimo MS450P22 decoders cost £275.95. The premium Sound Fitted Deluxe range (£299.95) adds motorised radiator fans synchronised to sound and tinted windscreen glazing. Four distinct sound projects cover Original 37/0, Thermostatically controlled fans, 37/4, and DRS-modified variants. Available liveries span BR green (D6710, D6829), BR blue, Large Logo blue, Railfreight sectors, Civil Engineers 'Dutch', Regional Railways, InterCity Mainline, DRS, and Colas Rail.

Accurascale entered the market in 2023 with unprecedented detail levels using 3D laser scanning to capture accurate tumbleholme, nose curves, and cab roof profiles. Their 21-pin DCC socket models feature timeframe-specific details including split headcode displays with selectable four-character codes, operating roof fans synchronised to DCC sound, and comprehensive tooling variations for different eras and regions. Standard models retail at £169.99 with DCC Sound Fitted versions at £259.99. However, Accurascale produces limited runs of just 25-50 units per variant, making pre-ordering essential. Batch 1 (2023) sold out rapidly, Batch 2 delivered in early 2024 with Western Region variants featuring unique lamp irons, and Batch 3 is scheduled for Q4 2025 introducing the first OO gauge Class 37/9 Mirrlees-powered variants alongside additional 37/4 models in EWS, Colas, and other privatisation-era liveries.

Hornby continues producing their original 1980 tooling in the Railroad Plus range, offering a budget entry point at £85-£95 (catalogue number R30185). Whilst lacking the sophisticated features of Bachmann or Accurascale models, Hornby locomotives provide reliable basic operation and wide secondary market availability of older releases in various liveries.

N gauge modellers rely primarily on Graham Farish (Bachmann Europe's 2mm scale brand) for ready-to-run BR Class 37 models. The current tooling introduced in 2014 features a 5-pole motor with twin flywheels, diecast chassis block, all-wheel electrical pickup, 12-wheel drive, and 6-pin DCC decoder socket. Directional lighting includes high-intensity headlights on refurbished locomotive variants. The 371-xxx series catalogue offers Class 37/0 centre headcode variants and Class 37/4, 37/5, 37/6 refurbished subclasses across extensive livery options: BR Large Logo blue, Railfreight Grey/Red Stripe, Railfreight sector triple greys (Distribution, Petroleum, Metals, Construction), Regional Railways, DRS (multiple versions), West Coast Railways maroon, and Colas Rail orange/black. Pricing ranges from £131.70 to £154.95 (RRP). Special editions include the Avro Vulcan Collector's Pack (370-375) featuring 37558 "Avro Vulcan XH558" with a pair of Avro Vulcan aircraft models.

O gauge enthusiasts can choose Heljan's comprehensive range of 7mm scale models. The 2024 retooled split headcode range (catalogue numbers 3720-3728) represents the pinnacle of O gauge Class 37 modelling with twin five-pole motors (one per bogie), brass flywheels, ESU XL decoder socket/DCC Ready with screw terminals, LED directional lighting, powered roof fan (motorised), interior and exterior LED lighting, provision for large speaker and smoke unit, sprung buffers, finescale metal screw link couplings, factory-fitted bufferbeam cables/hoses, and etched metal grilles. Multiple tooling variations accurately represent cast/fabricated bogies, boiler-fitted/isolated configurations, and nose-end variations across different production batches. Available liveries include BR Green (various yellow panel configurations), BR Blue, Large Logo Blue, Railfreight sectors, Civil Engineers 'Dutch', DRS, and EWS Red/Gold, both numbered and unnumbered options. Prices range from £495 to £669 depending on specification and features. Earlier 2017-2019 centre headcode variants remain available offering alternative subclass representations.

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