The British Rail Class 52 is a class of 74 Type 4 diesel-hydraulic locomotives built for the Western Region of British Railways between 1961 and 1964. All were given two-word names, the first word being "Western" and thus the type became known as Westerns. They were also known as Wizzos and Thousands.^[1] The final Class 52 locomotives were withdrawn from service in 1977.

When switching to diesel traction as part of the Modernisation Plan of the 1950s, British Railways (BR) designed, and commissioned designs for, a large number of locomotive types. At this time BR's regions had a high degree of autonomy, which extended as far as classes of locomotives ordered and even the design criteria for those locomotives. Whilst almost all other diesel locomotives were diesel-electric, the Western Region employed a policy of using diesel-hydraulic traction, originally commissioning three classes of main line locomotives: a type 2 and two type 4s (later designations Class 22, Class 41 and Class 42). With pressure to increase the speed of the transition from steam to diesel, volume orders for the Class 22 and Class 42 (along with a similar design Class 43) followed in 1957, a mere two years after the original orders and well before any idea of performance or reliability could be gained. At the same time it was realised that all the existing orders (diesel-electric and diesel-hydraulic) were for types 1, 2 and 4; thus orders were placed for 101 Type 3 diesel-hydraulics (later Class 35). However the increasing demands for more powerful locomotives prompted a further order, in 1961, for 74 diesel-hydraulics of 2,700 hp (2,000 kW); so when the first locomotive was outshopped from Swindon Works in December 1961, less than a year after the order was placed, the Westerns were born.^[2][3]

The theoretical advantage of diesel-hydraulic was simple: it resulted in a lighter locomotive than equivalent diesel-electric transmission. This provided a better power/weight ratio and decreased track wear. Unfortunately, it had several key disadvantages:

• The technology was proven in continental Europe, particularly Germany, but was new to the UK. At the time, it was considered politically unacceptable for the UK government to order railway rolling stock from foreign companies, especially German companies so soon after the Second World War. This resulted in most of the engines and transmissions being manufactured in the United Kingdom under licence from the German manufacturers.^[4]
• The most robust hydraulic transmissions were only capable of handling engines with power output of around 1,500 hp (1,120 kW); building a more powerful locomotive would involve two diesel engines and two transmissions.
• The transmission had significantly higher power losses than diesel-electric, negating some of the benefits and resulting in considerably higher fuel consumption.^{[citation needed]}

Experience showed that the Bristol-Siddeley-Maybach engines were superior to those made by North British Locomotive Company-MAN and although the use of twin engines in the same locomotive was new, the design did not produce any insurmountable problems. In the end the diesel-hydraulic experiment foundered on low fleet numbers, poor maintenance conditions and design issues; not on its German heritage or development of a novel configuration. BR's Swindon Works maintained all the diesel-hydraulic locomotives, and their early demise resulted in a much reduced workload and hastened its eventual closure in 1986.

With the Hymeks and Warships already in service but proving underpowered for top-link services, BR Western Region needed a high-powered locomotive for these trains – the Western therefore needed two diesel engines to achieve the required power output. In keeping with their policy, a new locomotive with a hydraulic transmission was envisaged. Experience had shown that the Maybach engines in the Hymeks were superior to the earlier Maybach and MAN engines used in the Warships, particularly in power output. Also Maybach were able to offer their 12 MD engines rated at 1,350 bhp (1,010 kW) allied to a Voith transmission; a Mekydro transmission designed to handle such power could not be fitted into the British loading gauge.

Prototypes sited the engines behind the driving cabs but drivers found this too noisy; moving the engines centrally meant making the locomotive heavier, removing some of the design's advantage. In operational use, the dual-engine arrangement turned out to have some advantages: in particular, the Westerns were able to continue operating with a single engine running in situations where more conventional single-engine designs would require rescue by another locomotive.

The most serious continual problem with the class was a mismatch between the Maybach MD655 engines and the Voith L630rV three speed hydraulic transmissions, a design fault. The top gear ratio in the transmission was too high for the torque characteristics of the engine: the result was that a single locomotive could struggle to reach its claimed 90 mph (140 km/h) top speed in the absence of down grades, more so when work-weary and due for overhaul. This factor, the South Devon Banks (a major part of their running grounds) and the deleterious effect on worn-out engines, all contributed against the Westerns continuing in top-line service. With fifty Class 50 locomotives becoming available following completion of the West Coast Main Line electrification, and new High Speed Trains, the speed and comfort increases the Western Region sought could be achieved and the Westerns dispensed with. Towards the end of their careers, the Westerns were all allocated to Laira (Plymouth).

More information Code, Name ...

Distribution of locomotives,
July 1967^[5]

82A 84A
Code	Name	Quantity
82A	Bristol Bath Road	15
84A	Laira	59
Total:		74

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Whilst the design was largely successful, the working life of the class was relatively short. Its non-standard design added to its maintenance costs at a time when national British Rail policy was moving away from diesel-hydraulics. When the Westerns were introduced in 1962, the Western Region had 226 diesel-hydraulics and 10 diesel-electrics (excluding shunters); by 1966, the numbers were 345 and 269 respectively. As a result, the early 1970s saw the decision taken to retire all the diesel-hydraulic types. Class 46s and Class 47s took over passengers and heavy freight, Class 31s and Class 37s took over light passengers and freight, and Class 25s covered the lighter duties. Following completion of the electrification of the West Coast Main Line throughout from London to Glasgow, the Class 50s were reallocated to the Western Region; the introduction of High Speed Trains three years later was the final nail in the coffin for the Class 52 Westerns.

In 1968–69, the Westerns received train air brake equipment in addition to their vacuum exhausters, thus significantly extending their working lives, unlike the similar but lower-powered, Warship class. Four of the class (D1017–D1020) did not receive dual brakes, with these locomotives being among the first withdrawals. The vacuum brake equipment was retained and to fit the additional equipment, it was necessary to remove one of the fuel tanks.^[6] However, as with the Warships, it proved impossible to equip them with electric train heating (ETH, or head-end power in US terminology). The Western Region faced particularly stiff competition for its prime inter-city services in the mid to late 1970s from the M4 motorway and it was generally felt within BR that significant speed and comfort improvements on the prime London Paddington-Bristol route were necessary. The lack of ETH meant the Westerns could not power the newly introduced air-conditioned BR Mark 2d/e/f coaches – a shortcoming that classes 47 and 50, equipped with ETH (the latter from new), did not share.^[7]

The highest recorded speed with a Western that O. S. Nock was aware of was 102 mph (164 km/h) when D1068 hauled nine coaches (305 tons gross) down 1 in 1,320 (i.e. virtually level) at Southall. The train averaged exactly 100 mph (161 km/h) for 12.8 miles (20.6 km) between Slough and Ealing whilst hauling a service from Reading to Paddington.^[8]

However, when it came to drawbar horsepower the Westerns in some respects were less capable than the equivalent diesel electric locomotives. Nock states "whilst the Westerns took their rightful place as fast and powerful locomotives it became evident that they were showing the same deficiency in actual power put forth at the drawbar as the [diesel-hydraulic] Warships had done. The highest output that came to my notice was a sustained 85 mph (137 km/h) hauling 560 tons descending 1 in 1,320, which equates to 1,500 edhp (equivalent drawbar horsepower)".^[9] A similar result was obtained when Clough & Beckett^[10] compared the performance of type 4 diesel locomotives (Classes 45/46/47/50/52) hauling trains up the ascent to Whiteball summit. They deliberately chose data to show each class in their best light and included a Western run which produced 1,775 edhp but they still concluded that "without doubt the Westerns get the wooden spoon; certainly not what one would expect from units of 2,700 bhp". The best performer was the Class 50, a 2,700 hp (2,000 kW) diesel-electric locomotive: on one run this achieved 2,115 edhp.

Despite this apparent limitation, the BR Western Region load-limit book gave the same 550 ton loading figure for both the Class 52 and Class 47 diesels over the South Devon banks between Newton Abbot and Plymouth. The reason for this is that, while the diesel-electric classes could produce high maximum tractive effort for limited periods, diesel hydraulics could produce significantly higher continuous tractive effort.^[4]

This section needs additional citations for verification. (May 2023)

While the first Western was under construction, proposals for livery and names were prepared by the BR design panel. The D1000 series locomotives were to be named after famous West of England place names; the illustration from the portfolio shows D1000 bearing the name Cheddar Gorge. This was not followed in production, however, and the Westerns were named with general heraldic and regimental terms prefixed with the word "Western" as per the following table.

Of the 74 locomotives built, 7 have survived to preservation.

Although designated Class 52 under the TOPS scheme and all were still in service when TOPS was introduced in 1973, no Western ever carried its "52 0xx" TOPS number. As withdrawal was already planned when the scheme was introduced and because of the cast number plates, it was not considered cost effective to renumber the locomotives. Some class members did run with the "D" of their number painted over – TOPS classification removed the need for locomotives to indicate their energy type in the running number (D = Diesel, E = Electric).

When the display of destination headcodes on the front of trains was dropped in 1976, the instruction was given for them all to be set to "0000". On many Westerns, the headcode was set to display the locomotive's number in contravention of this directive and most surviving members of the class ran like this until they were scrapped. If used for routing, such reporting numbers would be interpreted as a passenger express terminating on the Southern Region.^[20]

• 15 August 1963. Knowle and Dorridge rail crash. D1040 Western Queen^[22] collided with a freight train, crushing the cab and killing the three traincrew.^[23] The locomotive was repaired and returned to service.
• 11 January 1967. St Annes Bristol rail crash. No. 1071 Western Renown in charge of the diverted 12:00 Paddington to Swansea collided with the rear of the 11:45 Paddington to Bristol hauled by No. 1067 Western Druid. The collision resulted in very severe damage being caused to the leading cab of locomotive No. 1071, but the three men in the cab escaped injury by moving into the centre of the locomotive. Nineteen passengers required first aid or medical treatment but there were no fatalities or serious injuries. The locomotive was repaired and returned to service.^[24][25][26]
• 19 December 1973. Ealing rail crash. No. 1007 Western Talisman derailed while hauling an express passenger train, after an unlocked battery box door fell open, broke off and changed points under the locomotive. Ten people were killed.^[27] The locomotive did not return to service.
• 29 January 1975 (Oxford). No. 1023 Western Fusilier derailed with a London Paddington to Birmingham train whilst approaching the platform. This was due to a failed axle which had split due to the growth of a previously undetected crack. There were no reported injuries and the locomotive was later preserved.^[28]
• 3 January 1976 (Worcester Tunnel). No. 1055 Western Advocate crashed into a stationary parcels train killing the driver and guard of the Western.^[29] The locomotive did not return to service.

Withdrawal of the class began in May 1973 with D1019 Western Challenger and D1032 Western Marksman becoming the first members of the class to be withdrawn. The final five engines in service were withdrawn in February 1977, these five engines would also survive into preservation with D1023 being donated to the National Collection.^[30][31]

Seven locomotives have survived into preservation at heritage railways, four Swindon built & three Crewe built. Two have run on the mainline in preservation with D1015 being passed to operate on the mainline since 2002.^[32][33] D1062 made a brief appearance in 1980 during the Rocket 150 parade at Rainhill.

D1022 Western Sentinel was a candidate for preservation and was planned to be purchased by the DTG (Diesel Traction Group), but it was scrapped. D1015 Western Champion was purchased for preservation.^[34]

The first model of a Class 52 was produced by Trix (company) to its unusual compromise scale of 3.8mm to 1ft with OO gauge/HO gauge (16.5mm) track. This model, however, was quite crude.

In 1979 Hornby Railways launched its first version of the BR Class 52 (type 4) Western in OO gauge.^[38]

Lima (models) also produced a model to OO gauge.

An N gauge model was produced by Graham Farish.

Since then, OO gauge models have been produced by both Heljan, and most recently Dapol, whilst an O gauge model has been produced by Heljan. Dapol have also produced a model in N gauge.

• Krauss-Maffei ML 2200 C'C', Renfe Class 340, contemporary twin engined, twin transmission C'C' diesel hydraulic locomotives
• Voith Maxima, modern (2000s) single engined, single transmission high power diesel hydraulic locomotive