British Rail Class 37


Built by English Electric between 1960-1965, the British Rail Class 37 (English Electric Type 3), was the mainstay of the British Rail diesel locomotive fleet. With its versatile design, it had the capability to haul heavy freight trains, as well as mainline passenger services. The Class 37 was unique, as there was no prototype locomotive, it was built using the proven design of the Class 40 locomotive, which was introduced a few years earlier in 1958.

Ordered as part of their modernisation plan, British Rail wanted a versatile and reliable diesel-electric locomotive to be the backbone of their fleet. The modern engineering and power of the Class 37 met all the criteria, being able to operate almost anywhere on the network. The solid build quality of the locomotives is evident, as today, sixty of these workhorses are still in active service, along with thirty more in preservation. This is a testament to the quality craftsmanship of English Electric, making their units built to last for over half a century.

Richard Dyke

In 1958, British Rail placed their order with English Electric for the Class 37. Because of the large volume of locomotives ordered, they were constructed at two locations, Vulcan Foundry and Robert Stephenson and Hawthorns, both of which were well-known locomotive builders. Upon delivery in 1960, the first 119 locomotives were delivered in British Rail green with a silver roof, and contained split headcodes. Later Class 37s contained headcodes that were in the center of the nose. The Class 37 housed an English Electric 12CSVT prime mover capable of 1,750 horsepower. British Rail continued to place orders for the locomotive until 1964.

The Class 37 could be seen anywhere on the national rail network, as it is versatile and could complete any task with ease. Rail enthusiasts always recognise the sound of the Class 37, as the prime mover has an unmistakable growl, which later led to these locomotives being nicknamed “tractors”. Adding to its versatility, the Class 37 has a route availability of 5, which made it useful on many branch lines. This is due to the Class 37 having a low axle load, allowing the locomotive to operate services on any line with ease.

Where a Class 37 operated could be identified by its headcode. Prior to 1980, a split headcode Class 37 could be seen working in northern England. Most of the Class 37’s that had a center headcode were designated to the Western region of England and Wales.


The reliability of the Class 37 did not go unnoticed, as they were seen as the definitive type 3 locomotive, and were slated for rebuild to extend their lifespan. Rebuilds consisted of rebuilding or the addition of any component, including Electric train heating, new trucks, and some even received new prime movers. There are seven subclasses of Class 37s.


This type of Class 37 was kept original as delivered and did not receive any substantial upgrades. The only difference within this subclass was the split and center headcode variations.


This subclass received new bogies, the CP7. At one time, radial self-steering trucks were tested to reduce rail wear and noise, however, it was deemed too expensive.


The 37/4 subclass was primarily used for passenger service. This class received electric train heating (ETH) which allowed the locomotive to power the passenger cars with lights and heat. This class was also given new CP7 bogeys, additionally , the English Electric generator was replaced by an alternator, supplied by Brush traction. These units received upgraded wiring, and painted in the BR Blue “large logo”, introduced in the eighties. These units found use in Scotland and Wales, Scotland received 25 units, and Wales received six units. They served passengers for many years, later, they were turned into freight locomotives, primarily Transrail freight units, which was based in the western portion of the country.


The 37/5 subclass received updated wiring, and CP7 bogeys. These locomotives were relegated to freight use and were painted in British Rail’s “3 tone gray” paint scheme.

Class 37 in freight gray livery.
Hugh Llewelyn photo


The 37/6 subclass were modified versions of the 37/5 subclass. These units were owned by Eurostar in anticipation of operating an overnight sleeper service through the channel tunnel and into continental Europe. However, this service never came to fruition and Eurostar sold many of their twelve Class 37s to Direct Rail Services (DRS). Furthermore, many of the 37/6 subclass can be found hauling electric multiple units (EMUs) under the ownership of Rail Operations Group’s “Europhoenix”.


The 37/7 subclass was primarily used for freight traffic. This subclass was closely related to the 37/5 subclass, the only difference being the side window was plated over, and extra weight was added for additional tractive effort. These locomotives were commonly located in South Wales hauling heavy coal and metals trains.

With the addition of the Class 56 and Class 60s, which were substantially more powerful than the Class 37s, many 37/7s were removed from service and sent to countries within continental Europe for freight and work trains duties.


Perhaps the most unique of the subclasses is the Class 37/9. These units were completely rebuilt, receiving new Brush alternators, updated wiring, added weight, and a new prime mover, either a Mirrlees MB275T or a Ruston RK270T. These units were used as a test bed for the future Class 38 locomotives that never came to fruition.  Much like the Class 37/7s, these units also had their side windows plated over. Additionally, the exhaust on these units had to be modified to accommodate the new prime mover.

Intended for freight service, these units were delivered in Railfreight gray, and were assigned to the coal and metal trains in South Wales. Upon delivery of the newer and more powerful Class 66 locomotive, the Class 37/9s were gradually phased out, and put into storage.

Phil Richards photo

Role in Modernisation

As part of the modernisation plan, British Rail sought to eliminate the use of steam locomotives from the national rail network. With the order of the Class 37, steam was extinguished by 1968. The Class 37 took over the duties of the steam locomotives, and provided crews with the comfort and ease of operation that a diesel locomotive has to offer. The modernisation plan called for a universally modern railway, with reliable locomotives that improved efficiency and passenger comforts.

Current Day Owners

Direct Rail Services (DRS)

Direct Rail Services currently has twenty-one active Class 37 locomotives. Many of which are in passenger service and were leased to Northern Railway for use of the Cumbrian Coast Line, due to the lack of diesel multiple units (DMUs). The DRS Class 37s can also been seen hauling passenger trains in the Greater Anglia region of the country.

Direct Rail services is one of the UK’s premier freight train operators. DRS was primarily contracted to transport nuclear flasks from Scotland, additionally, DRS handles intermodal traffic as well.

Colas Rail

Colas Rail currently owns fourteen Class 37s. Many of these are units that were previously in preservation, however, have been pushed into service. A few of these Class 37s serve on rail head treatment trains that operate overnight. Colas Rail is a UK freight operator that focuses mainly on shipping aggregates, which are materials commonly used in construction.

West Coast Railways

West Coast Railways, a spot-hire charter railway company, owns eleven Class 37s. However, six of these Class 37s are either in storage or undergoing repairs. West Coast Railways is a charter railway that offers special services, such as dinner trains.

Rail Operations Group

Rail Operations Group has six Class 37s that are on lease from Europhoenix. Europheonix is a spot hire railway leasing company, who is known for their low cost leasing services.

Network Rail

Network Rail currently operates three Class 37s which are commonly used on inspection and work trains.Network Rail is the agency responsible for maintaining railway tracks throughout the United Kingdom. As well as lease the track out to train operators.

Preservation Efforts

Currently, thirty Class 37s are preserved, either in museums or in working order. One of the most prominent Class 37 preservationists are the dedicated team of the Class 37 locomotive group. This group owns Class 37 37003, and is currently undergoing restoration to be used on the Mid Norfolk Railway. Additionally, The National Railway Museum also houses a preserved Class 37, delivered as D6700, which is the first of the class to be delivered to British Rail.


Wheel ConfigurationCo’Co’
Wheel diameter3 ft 9in.
Wheelbase50 ft 8 in
Length61ft 6in
Width8 ft 101/2 in
Height12ft 9in
Weight100 long tons
Fuel Capacity890 gallons imperial
Max Speed90 mph
Tractive EffortMax: 55,500lbf. Continuous: 35,000lbf
Route Availability5
For more information on the Class 20, Pip Dunn’s book “British Rail Class 20 Locomotives” provides an in depth study of the locomotives. (Link to Amazon)


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