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TheBritish RailClass 43 (HST) is theTOPS classification used for theInterCity 125High Speed Train (formerly Classes 253 and 254)diesel-electric power cars, built byBritish Rail Engineering Limited from 1975 to 1982, and in service in the UK since 1976.
The class is officially thefastest diesel locomotive in the world, with an absolute maximum speed of 148.5 mph (239.0 km/h), and a regular service speed of 125 mph (201 km/h). The record run was led by 43102 (43302) and trailed by 43159.[3][4]
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In the early 1970s, theBritish Railways Board made the decision to replace its main-line express diesel traction. Financial limitations were tight, so mass electrification was not possible. As a result, a new generation of high-speed diesel trains had to be developed.
Experience with the high-speedClass 55Deltic locomotives had shown that a low axle weight was essential to avoid damage to the track at sustained high speed, with sufficient power-to-weight ratio for a high speed train.Gas turbines had been considered as an alternative powerplant for the type but they were costly, were fuel hungry and also had high maintenance requirements and were thus ruled out in favour of a more conventional pair of diesel engines.[5] To power the HST at up to 125 mph (201 km/h), an arrangement of two medium-power diesel engines was opted for instead. It was not possible to position both engines within a single power car due to the low axle weight required, hence a pair of power cars, each equipped with a single engine, were used instead.[5] The power car had a design weight limitation of 70 tonnes: to fulfil this required the use of lightweight equipment that still satisfied the necessary levels of strength, reliability, and reasonable affordability to accommodate the high planned utilisation rate for these vehicles;[5] the 70-tonne weight of the power car achieved a 17.5-tonne axle loading.
It was designed by the British Railways Board Chief Mechanical & Electrical Engineer's Department at theRailway Technical Centre in Derby in collaboration withBritish Rail Research Division and various equipment manufacturers. Principal manufacture was performed byBritish Rail Engineering Limited (BREL); specifically, while the power cars were produced atCrewe Works, the accompanying trailer cars were built atDerby Litchurch Lane Works in Derby.[5]
To validate the design, a prototype set was produced. The engine used in the prototype power cars was the Paxman 'Valenta' 12RP200L, which developed 2,250 horsepower (1,680 kW). Despite being placed at opposing ends of the train, the two power cars were connected to one another via cables that ran the length of the train, permitting the leading cab to exercise effective control of both power cars.[5] Each power car had a main driver's position at one aerodynamically shaped end with the other flat and gangwayed end having only an auxiliary driving position for shunting purposes.
The two prototype power cars emerged from Crewe Works in June and August 1972 and were initially numbered41001 and 41002, but after a short period the entire set, including the passenger coaches, became reclassified as a diesel-electric multiple unit:British Rail Class 252. The power cars were given the coaching stock numbers 43000 and 43001. After proving trials on the Eastern Region the prototype High Speed Diesel Train (HSDT) was transferred to the Western Region, where it was deployed on Paddington – Bristol – Weston-super-Mare services.

The design was successful and led to production orders being placed for similar trains for the Western, Eastern, Scottish and London Midland regions. The production power cars featured a redesigned front end without conventional buffers, although a rigid drawbar can be used to connect an HST to an ordinary locomotive. Following the introduction of production HST sets, the prototype unit was withdrawn, the power cars passing to the Research Division at Derby. Of the ten prototype coaches, two were adapted for use in theRoyal Train,[6] five were modified for use with the production HSTs,[7] and three were transferred to Departmental stock.[8]
The 197 power cars produced are numbered 43002-43198. 43001 was applied to the second of the two prototype power cars, while the first of the pair (now preserved at the NRM; formerly operational on the GCR) became 43000, which is unusual because BRTOPS classification numbered its locomotives from 001 upwards (this was because it was not, at the time, classified as a locomotive).

In 1987, as electrification of theEast Coast Main Line was under way, British Rail realised that the newMark 4 carriages for theClass 89 andClass 91 locomotives were not going to be finished in time for the introduction of electric services on the East Coast Main Line so, in late 1987, a total of eight Eastern Region power car conversions were carried out at the Derby Engineering Development Unit, whilst the other six were converted by the diesel repair shop at Stratford to have the lower valancing removed and buffers fitted.
After being fitted with buffers, these power cars began work as surrogate DVTs to work with the Class 91s and 89. The locomotives, working with conventionalMark 3 stock, worked on the line between 1987 and 1991, when the last Class 91 locomotives entered service. As well as buffers being fitted to these power cars, special remote control equipment was also added to the locomotives so they could be controlled by the locomotive at the front. Once these locomotives left DVT duties, the remote equipment was removed.
After privatisation, these power cars joined the Virgin Trains fleet working bothVirgin CrossCountry andVirgin Trains West Coast routes, where they displaced loco-hauled stock. All the units were repainted from their original InterCity colours to the Virgin red livery. Later, Virgin Trains withdrew the HSTs when newClass 220 and221 units were delivered, and nearly all of these power cars went into storage at Long Marston.
After years of storage, several of the power cars were bought byMidland Mainline to be part ofProject Rio, special services running fromLondon St Pancras toManchester while major engineering works were undertaken on theWest Coast Main Line. These units were kept in the de-branded Virgin Trains livery throughout their time with Midland Mainline and put back in storage once Project Rio had finished in 2006.
Two units joined Network Rail'sNew Measurement Train in 2003 and have continued to work with this service ever since. Both of these units have now hadMTU engines fitted.
One unit was leased to GNER as a one-off power car, working as a spare unit that could be easily called for if an HST failed. For most of its time with GNER, it was based at Craigentinny yard in Edinburgh and was painted into GNER colours. This locomotive's lease ended in 2006 and it was returned to storage at Long Marston.
In 2007,Grand Central took an interest in the stored power cars and amalgamated them into its fleet of three HST sets. In total, six were bought by the company and ran high-speed services between Sunderland and London Kings Cross. Two were the final operationalPaxman Valenta power cars, being re-engined in 2010 with the MTU treatment. While at the works being re-engined, Grand Central added the orange stripe that appears on itsClass 180 units, re-painted the front ends (making them look more like the non-buffered HSTs), and re-numbered the power cars into the four-hundreds. They were withdrawn from Grand Central service in 2017 after more Class 180s were acquired.[9]
British Rail experimented withMirrlees Blackstone MB190 engines in four Western region examples (43167–43170) between 1987 and 1996, but this experiment was unsuccessful and the standard Paxman Valenta engines re-installed.
Paxman began development of the Valenta's successor, thePaxman VP185, in 1987. The suggestion that British Rail participate in a trial of the new VP185 engine in the IC125 was first mooted in January 1991, and a formal agreement for the trial was signed in May 1993.[10]
A qualifying requirement for the trial was that the engine should undergo a British Rail Type Test which was carried out between December 1993 and February 1994.[10] The test involved completion of 3,000 cycles, each of 10 minutes duration, with four minutes at the maximum power of 2,611 kW (3,501 bhp) and six minutes at idle, simulating the typical 'on-off' nature of IC125 duty. The test was much more severe than operational duty, where the train operates at a maximum of 1,678 kW (2,250 bhp). The successful results of the test cleared the way for installation of a VP185 in Power Car 43170 at Plymouth Laira Depot for in-service trials in the summer of 1994. Power car 43170 entered service on 22 September 1994.[10] 43170 was given the nameplate "Edward Paxman".[citation needed]
During the late 1990s twenty-five HST power cars were re-engined withPaxman VP185 engines in order to improve fuel consumption and reduce emissions.
The last VP185 engine to be manufactured at Paxman's Colchester Works was despatched from the factory on 15 September 2003 as part of a programme to convert 14Midland Mainline power cars to VP185 engines to supplement the four already converted during 1994/95, and this led to 43043/045/048-050/052/055/060/061/072/073/076/082 joining 43047/059/074/075 with this engine type.[11]
Today there are no production power cars fitted with a Paxman Valenta engine, although the 125 Group have reinstalled a Paxman Valenta in the survivingprototype power car, 41001 (formerly 43000). The 125 group are also in the process of reinstalling a Valenta into 43044 for preservation.[12]
In 2007,Brush Traction andHitachi equipped Paxman Valenta powered 43089 and a semi-permanently coupledMark 3 coach with a diesel-batteryhybrid power system for experimental trials. The power car was named "Hayabusa" (Hayabusa, はやぶさ, Japanese forPeregrine falcon, project name 'V-Train 2').[13][14][15] It returned to normal service with East Midlands Trains.
The body structure of the Class 43 comprises integral all welded, mild steel construction across both the underframe and the stressed skin bodyside.[5] This structure was optimised usingcomputer aided design andfinite element analysis. Material thickness varies from 10 mm (0.39 in) across the majority of the underframe to 2.5 mm (0.098 in) on the bodyside frame pressings and 2 mm (0.079 in) for the bodyside skin.[5] The body was internally divided by a pair of transversebulkheads, one at the rear of the driver's cab and the other at the forward end of the luggage compartment; a self-draining sealing plate floor was installed between these bulkheads that collected any spillage within a tank located beneath the underframe. All of the air intakes are positioned as high as possible and fitted with disposable dry filters where deemed to be necessary.[5] A secondary bulkhead separated the engine from the clear air compartment, in which the electrical apparatus, control and brake equipment were housed.[5]
The cab is amonocoque demountable unit furnished with astreamlined nose that was directly mounted on the underframe. The individual inner and outer skins are composed ofglass reinforced polyester that, in combination with apolyurethane foam core, forms a high strength to weight composite structure.[5] In comparison with legacy traction, the crew environment was improved in multiple respects, including a reduction in noise levels and protection from minor impacts even at high speeds. The ergonomics of both the driving position and controls were intentionally designed though anthropometric data that sought to facilitate precise control and minimise driver fatigue. The cab isair conditioned to maintain a temperature between 20 and 22 °C (68 and 72 °F).[5] A door in the cab bulkhead provides access to the electrical compartment, engine room and cooling units, which can be traversed to reach to the luggage compartment and guard's compartment, which is able to be locked to form a security compartment. A through vestibule provides access to the rest of the train. For additional maintenance access, the roof is outfitted with removable sections of aluminium and GRP.[5]
Each powercar was powered by a singlePaxman Valenta 12 cylinder 4-stroke diesel engine. It had a maximum continuous rated output of 1,500 rpm and developed up to 2,250 bhp (1,680 kW).[5] The Valenta engine had been developed from the preceding Ventura that had been used to power various forms of rail traction since 1958. The direct-driven alternator set was directly mounted to the engine while the complete power unit was mounted on the underframe.[5] The combustion air was filtered and ducted to the engine'sturbocharger. The fuel oil, sufficient to cover a distance of 2,300 km (1,400 mi) was stored within tanks beneath the underframe, was filtered, de-aerated and water-separated. The engine was also fitted with a conventional exhaust pipe and silencer; a roof mounted scavenging fan ventilates the engine room.[5] Electric power was produced by a three-phasealternator set, built byBrush, was rated for an engine output of 1,868 kW (2,505 hp); the primary alternator achieved a rectified output of 1,484 kW (1,990 hp) at 1,500 rpm.[5] An auxiliary alternator, which supplied power to the train, air conditioning, kitchen, and other auxiliary equipment, was also present. Each power car featured four frame-mounted traction motors, each of which had its own 3-point suspension on the bogie frame; this arrangement necessitated a flexible drive between the traction motor and the axle mounted gearbox to accomidate axle movement.[5]
A twin-circuit aluminium alloy cooling unit, designed byVoith and produced by Marston Excelsior, cooled the water of the engine jacket, combustion air and lubricating oil systems.[5] The single fan is driven by a shaft from the engine via a bevelgearbox and thermostatically controlled fluid coupling, both of which are cooled by Marstonheat exchangers. Mechanically-driven pumps are used for coolant circulation. Particular attention was dedicated paid to achieving a leak-proof system; this led to the use of flanged hoses and simplified pipe runs where practical to do so while the cooling water contains bothanti-freeze andcorrosion-inhibiting agents.[5] Each power car was provisioned with a pair of 5.4 kg (12 lb) portablefire extinguishers as well as fixed fire fighting installations that acted to protect key equipment within the car body against fire hazards.[5] Specifically, this installation used a 18.2 kg (40 lb) bottle ofbromochlorodifluoromethane (BCF) that was discharged via a distribution pipe network; actuation was achieved via pull handles situated in the driver's cab and on the bodyside. Furthermore, an automatic fire detection and alarm system was present; this consisted ofheat detectors, a test button and an alarm bell.[5]
Thebogie features a welded mild steel frame and was furnished with monobloc wheels.[5] It was equipped withdisc brakes (which comprised cast iron cheek plates) and radius links (to guide the axleboxes). Coil springs were used for the primary suspension while 'flexicoil' springs were used for secondary suspension; hydraulicdampeners controlled both the primary and secondary suspension along with lateral movements and high frequency bogie rotation. Pre-compressed rubber elements and a pivot casting were used to control forces from both traction and braking.[5] The electrically-controlled automaticair brake system, which was distributed across the whole train, conformed to BR's standard 2 pipe arrangement; despite this, it was able to bring the HST to a halt in less distance than contemporary locomotives travelling at only 100 mph (160 km/h).[5] Wheel slide prevention apparatus was also fitted upon all axles while cast iron tread conditioning brakes acted upon each wheel during brake application to maintain rail/wheel adhesion.[5]
The HST fleet, having been in operation since the late 1970s, has been largely replaced by theIntercity Express Programme.
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WhenCrewe Works built them, theInterCity 125 units were considered to bediesel multiple units, and were allocatedClasses 253 and 254 for Western and Eastern Region services respectively. The locomotives were introduced in the Midland region later.
Until the HST's introduction, the maximum speed of British trains was limited to 100 mph (160 km/h). The increased speed and rapid acceleration and deceleration of the HST made it ideal for passenger use, and it slashed journey times around the country. The prototype InterCity 125 (power cars 43000 and 43001) set theworld record for diesel traction at 143 mph (230 km/h) on 12 June 1973. An HST also holds the world speed record for a diesel train carrying passengers. On 27 September 1985, a special press run for the launch of a new Tees-Tyne Pullman service from Newcastle to London King's Cross, formed of a shortened 2+5 set, briefly touched 144 mph (232 km/h) north ofYork.
During 1987, eight HST power cars were converted for use as driving van trailers (DVTs) withClass 91 locomotives during trials on the East Coast Main Line. The power cars were fitted with buffers andtime-division multiplex equipment that allowed them to directly control a Class 91, and were moved over to the ECML where they were used on workings with Class 89 and then Class 91 locomotives from London to Leeds. After the Mk 4 stock had been delivered, theHST power cars had the TDM equipment removed, and then reverted to their normal duties. The power cars used for this project can be easily identified as they are still fitted with buffers. They were then transferred to Virgin Cross Country, and put in storage when Virgin replaced its HST fleet withBombardier Voyagers (thoughArriva, upon later taking over the franchise, acquired ten power cars, four of which were buffered).Grand Central bought six of these for services fromSunderland toLondon, the remaining two having been integrated into Network Rail'sNew Measurement Train.
After theprivatisation of British Rail the HST sets continued to be used. 193 of the 197 locomotives built remained in service, five power cars, 43173, 43011, 43019, 43140 and 43030, having been written off by fatal rail accidents in1997,1999,2004 and2020 respectively.

In 2018-19,Great Western Railway andLondon North Eastern Railway replaced their HST-worked services with ones operated byClass 800/801/802s. LNER retained none of its HSTs; GWR retained 24 power cars to form 11 four-carriage formations known as "Castle Class" sets for use on local services betweenCardiff andPenzance, which had not been worked by HSTs before.[18]
Twenty-seven sets each with four or five carriages moved from Great Western Railway toAbellio ScotRail and were refurbished with controlled emission tanks and plug automatic doors. These operate on services between eitherEdinburgh orGlasgow and eitherAberdeen orInverness.[19][20][21][22] The first two were delivered toCraigentinny TMD for crew training in September 2017.[23] The first entered service in October 2018.[24]
GB Railfreight have expressed interest in the possibility of converting displaced HST sets for use carrying parcels and other mail.[25]
In 2021,RailAdventure acquired the six 43/4 power cars, plus an additional two for spares, for use on stock movements as part of its entrance into the UK market through the acquisition of Hanson and Hall Rail Services.[26][27] Two were moved to Germany for display at a trade show in September 2021.[28] They returned in November 2021.[29]
On 25 November 2022, GWR announced it would be retiring their 'Castle' fleet. The withdrawals are expected to take place over a two-year period.[30]
In early August 2023, three power cars and 11 Mark 3 coaches were exported to Mexico for use on theTren Interoceánico.[31][32][33] They arrived in early September 2023.[34]
| Status/Operator | Image | Qty. | Vehicle nos. |
|---|---|---|---|
| Colas Rail | 10 | 43251, 43257, 43272, 43274, 43277, 43285, 43301, 43303, 43321, 43357[35][36] | |
| Great Western Railway | 12 | 43004, 43042, 43092–43093, 43097–43098, 43156, 43186–43189, 43198[36] | |
| Locomotive Services Limited | 9 | 43046–43047, 43049–43050, 43054–43055, 43058–43059, 43083[37][38][39] | |
| Network Rail | 5 | 43013–43014, 43062, 43290, 43299[40] | |
| RailAdventure | 8 | 43296, 43308, 43423, 43465, 43467–43468, 43480, 43484[40][41] | |
| ScotRail | 52 | 43003, 43012, 43015, 43021, 43026, 43028, 43031–43037, 43124–43139, 43141–43152, 43163–43164, 43168–43169, 43175–43177, 43179, 43181–43183[40] | |
| Tren Interoceánico | 11 | 43007, 43022, 43158, 43170, 43295, 43306–43307, 43316, 43320, 43378[42] | |
| First Metro (Nigeria) | 10 | 43008–43010, 43016, 43040, 43172, 43184, 43192, 43239, 43304, 43366[43] | |
| Preserved | 18 | 43002, 43018, 43023, 43025, 43044–43045, 43048, 43056, 43060, 43071, 43073, 43081–43082, 43089, 43159, 43165, 43302[44][40] | |
| Stored | 38 | 43017, 43020, 43024, 43027, 43029, 43063, 43066, 43076, 43088, 43091, 43094, 43122, 43153–43155 43160–43162, 43174, 43190–43191, 43194, 43206, 43238, 43305, 43309–43312, 43314–43320, 43367,[36][44][45] | |
| Scrapped | 28 | 43005, 43011, 43019, 43030, 43041, 43043, 43052–43053, 43061, 43064, 43069–43070, 43075, 43078–43079, 43086–43087, 43140, 43170–43171, 43173, 43180, 43185, 43193, 43195–43197, 43300, 43313[36][44][46][47][48] | |
On 2 May 2016 an open day was held atBristolSt Philip's Marsh depot with a line up of Class 43s from each operator (exceptCrossCountry) to celebrate the HST's fortieth anniversary. Several locomotives and passenger trains also appeared, such as150 247 and166 214 both in their new GWR liveries,158 798 in its Springboard Opportunity Group livery and the prototype Class 41 HST. At the event, power car 43002 (Numbered 253 001 as a Diesel Multiple Unit) was unveiled in original Intercity 125 livery, and namedSir Kenneth Grange after the Class 43's bodyshell designer.[49] On 2 October 2016, power car 43185 was unveiled in InterCitySwallow livery.[50] Both were operated by Great Western Railway (First Great Western) and 43002 is now preserved, Residing at the National Railway Museum at York.[51]
There have also been four serious incidents involving Class 43s; these accidents resulted in five power cars being written off.
There have been minor incidents involving Class 43s, among which have been:

The HST fleet is now in its sixth decade, and replacements are underway. This project, theIntercity Express Programme, is being spearheaded by theDepartment for Transport. A consortium headed by Hitachi has designed and built the new units, initially named "Super Express Train". Various formations are being built; both electric and bi-mode (electro-diesel) versions in five- or nine-coach lengths. The first batches have replaced HSTs on the Great Western Main Line and the East Coast Main Line.[citation needed]
On theGreater Western franchise, the last of the full-length HSTs was withdrawn in June 2019. Between 12 and 20 HST sets were originally to be retained and refurbished to carry on providing services between London, Devon and Cornwall, where no electrification was planned, and where the Class 800's diesel engines would not be capable of negotiating the steep gradients along the South Devon Banks, through to the mid-2020s.[71] A report published in 2011 concluded that the Mark 3 coaches could remain in service as late as 2035, subject to some minor rewiring and enhancements required under disability legislation.[72] However, it was announced in March 2015 that the HST would instead be replaced with theClass 802, a more powerful derivative of the bi-mode Class 800s.[73]
Initially, high-speedBombardier Voyager andAlstomClass 180Adelante replaced numerous HST units, but all locomotives and sets were brought back into service as a result of increasing demand. Some Great Western sets were cascaded to Abellio ScotRail to replace theClass 170 units, while others were retained by GWR to operate local services.[74] GWR will retire these units in favour of Class 802s by December 2023.[75]
Grand Central Railway leased five more Class 180 units cascaded from GWR to replace its HST trains and increase its overall fleet size.[76] This in turn allowed the HSTs to be cascaded toEast Midlands Trains.[77] The East Midlands Trains sets were passed to the newEast Midlands Railway franchise, which announced it would replace them with a combination of Class 180 and Class 222 units, enabled owing to the electrification of the MML as far north as Corby, to be replaced ultimately byClass 810 bi-mode units.[78]
Upon being retired, locomotive 43002 was preserved by theNational Railway Museum inYork.[79] It was joined by 43102 (43302)[80]
Nineteen Class 43 power cars have currently been saved for preservation.[citation needed]
The National Railway Museum in York has preserved 43002, the first production power car.[81] The Railway Heritage Designation Advisory Board nominated 43102 (43302) for preservation as holder of the record for being the fastest diesel locomotive on the planet.[82] The power car was donated to the NRM upon its withdrawal from service in May 2021,[83] and it is currently located at the NRM's museum atShildon.[84]
Angel Trains donated 43018 toCrewe Heritage Centre following its use as a spares donor forAbellio ScotRail.[85]Porterbrook also donated 43081, the 8,000th locomotive built at Crewe, to the museum in 2021. Porterbrook donated 43048 and 43089 to the125 Group. Both moved to the group when their lease ended withEast Midlands Railway.[86] The group later purchased 43044 from Porterbrook in 2021,[87] with 43159 being donated in June that year.[88]
43045 has been preserved at theLong Marston Rail Innovation Centre following its period in service withColas Rail and its time in storage.[89]

TheUniversity of Birmingham leased 43056 for use as aresearch & development vehicle.[90] In November 2021, the power car was donated to the Welsh Railways Trust based at theGwili Railway.[91] 125 Heritage Ltd, based at theColne Valley Railway, has saved five power cars, 43023, 43071, 43073, 43082 and 43165.[92]
In addition to these twelve,Locomotive Services Limited have saved seven power cars, 43046, 43047, 43049, 43055, 43058, 43059 and 43083 along with three sets ofMark 3 coaches for use on excursion trains. 43046 and 43055 have been refurbished and reliveried, along with a set of coaches, as a recreation of theMidland Pullman train.

In 1977Hornby Railways launched its first version of the BR Class 43 (HST) inOO gauge.[93][94]
Lima have released an HST model in OO gauge.[95]
Graham Farish andDapol have both released HST models inBritish N gauge.[96][97] Dapol introduced East Midlands Trains and Arriva Cross Country liveries, for the model, in 2012.[98]
New Measurement Train [HST] power cars Nos. 43013/014/062 have visited the [RIDC] at Old Dalby for 'first in class' testing...
43300, damaged in a collision atNeville Hill in 2019, has been scrapped.
43300 Scrapped [2025-01] bySandbach Commercial Dismantlers, Middlewich