You might not immediately recognise the term ‘Type 3 locomotives,’ but these diesel-powered machines have shaped Britain’s railways for over six decades. If you’ve ever traveled on a preserved heritage railway or seen a freight train rumbling past, there’s a good chance you’ve encountered one.

Born from Britain’s post-World War II push to modernise the railways, these locomotives were built for both passengers and freight services. Each class had its own strengths and technical innovations that made them indispensable.

In 1955, British Rail (BR) classified locomotives by engine output and Type 3 trains produced 1,500 and 1,999 bhp. Between 1960 and 1965, multiple Type 3 models entered service, each playing a unique role in reshaping the railway network.

Read on to explore these mighty British machines, their impact on railway history and how they continue to make their mark.

Class 37 trains (1960-today)

Between 1960 and 1965, English Electric built 309 diesel-electric Class 37 locomotives at Vulcan Foundry, Robert Stephenson & Hawthorns.

Unlike many earlier locomotives, the Class 37s were not built as prototypes before mass production. Instead manufactures worked directly from design specifications alone which helped to cut costs and accelerate production.

The first Class 37, D6700, was completed on 2nd December 1960 and marked what would become one of British Rail’s most enduring locomotive classes.

BR Class 37

BR introduced Class 37s for local passenger services and freight duties, helping replace ageing steam trains.

A key to their success was their compatibility with the Blue Star system, which allowed multiple locomotives to operate together under a single control unit. Their low axle loading also made them ideal for hauling long freight trains and navigating challenging routes, such as Scotland’s West Highland Line and rural Welsh railways.

Class 37s were largely used across the UK, including Yorkshire, the North East, Humberside, and the Eastern regions of England. Additionally, they took part in high-speed rail trials on routes like London Paddington to Bristol Temple Meads, though excessive wear and tear prevented further development.

Class 37 locomotive today

The Class 37 locomotive remains in service today, thanks to modifications that have extended its lifespan. 

Notable sub-classes include:

• 37/0:This is the original model number.
• 37/3: Reinforced with upgraded wheel frames.
• 37/4: Fitted with electric train heating for all-weather passenger services.
• 37/5: Equipped with Sandite dispensers to prevent wheel slippage on leaf-covered tracks.
• 37/6: Designed for an abandoned Channel Tunnel sleeper service.
• 37/7: Featured extra ballast (weight to increase the pressure between the wheels and the rails) and modified gearing to haul heavier freight.
• 37/9: Used to test new technology for the proposed (but scrapped), Class 38.

Over 60 years, Class 37s have sported multiple liveries, from their original green to Rail Blue and later franchise operator schemes.

Despite their age, some Class 37s remain in operation. A few owned by Harry Needle Railroad Company, are leased to construction giant Swietelsky (UK) for moving railway maintenance equipment.

Class 35 (1961-1975)

Built between 1961 and 1964, BR used Class 35 trains on secondary passenger routes. They earned the nickname “Hymek” due to their Mekydro hydraulic transmission, which also led to their downfall. The Mekydro system limited the number of locomotives a driver could control together, which hindered their operational flexibility.

The BR also used the 35 to bank freight trains on the steep Lickey Incline, near Birmingham. Banking involves one train pushing another up a gradient but it required modifications to prevent excess wear.

Their initial livery was striking, featuring a dark Brunswick green body, lime green stripe, a medium grey roof, and ivory white window surrounds. Some later received the standard BR Rail Blue livery with yellow warning panels.

The Class 35's lifespan was short and they were withdrawn from service between 1971 and 1975. You can still see some preserved units at West Somerset Railway, Severn Valley Railway, and East Lancashire Railway museums.

Class 33 (1960-today)

Built between 1960 and 1962 for the Southern Region, the Class 33 was the most powerful Bo-Bo diesel locomotive at the time, designed for everything from passenger services to heavy freight.

Key features of a Bo-Bo locomotive:

• Two bogies (the frames under the train that hold the wheels and allow the train to go around corners).
• Two axles on each bogie (the bars that connect and support the train wheels).
• Power to all axles from traction motors (to make the wheels turn so the train moves).

Originally, the Class 33 was intended to be a Co-Co locomotive (with six-wheeled bogies), but engineers opted for the Bo-Bo configuration for better speed and versatility.

The Class 33 trains stood out with their tough but stylish design. They included translucent roof panels and cab roofs, as well as distinctive head code panels which were particularly notable in the Southern Region.

There were three sub-classes:

• Class 33/1: Adapted for push-pull operation, drivers could control them from either end of the train, just like a tram.
  
  
• Class 33/2: Modified to fit through the narrow tunnels on the Tonbridge to Hastings line thanks to their slimmer design.
  
  
• Class 33 Tramway: These Class 33s moved fuel wagons and other equipment over lines in public streets on the Weymouth Harbour Tramway.

Today, most Class 33s are no longer in service. However, a few are still in use and you can visit them at various railway museums.

Find out more about the history of the Type 3s

To find out more, David Cable’s book 'British Type 3 Diesel Locomotives’ contains over 200 full-sized colour photographs of these workhorses in action.

Cable has written a range of very successful colour albums for Pen and Sword Books on the history of the British railways. His titles feature many unpublished photographs from his extensive collection.

Experience modern train travel with Avanti West Coast

Decades after their introduction, Type 3 locomotives remain a key part of Britain’s railway heritage. Their versatility and durability have ensured that some are still in service today. Others live on through preservation efforts across the UK.

From passenger services to heavy freight, these locomotives played a major role in modernising the railway network. Whether still in operation or restored for enthusiasts to enjoy, the legacy of the Type 3s continues to shape the story of British rail.