The UK rail network has a hidden history of unique and obscure locomotives - demonstrators and prototypes that push the limits of design and technology.

Here’s a look at some of the most fascinating, lesser-known engines and the stories behind them.

Builders' demonstrators

These prototype locomotives were designed to showcase new ideas to British Railways (BR). Many introduced technologies that shaped the trains we see today.

Here are some standouts:

10800

Built in 1950, the 10800 was BR's first road switcher and was designed for both  mainline routes and work in rail yards. Nicknamed 'The Wonder Engine' due to frequent faults, it was unpopular with drivers.

In 1961, Brush Traction bought the 10800, rebuilding it as the Hawk. They used it to test AC transmission as an alternative to DC.

10800 retired in 1968 and was finally scrapped in 1976.

D0280 (Falcon)

Brush built this 1961 diesel-electric prototype to test ideas for future Type 4  locomotives. Powered by two lightweight Maybach MD655 engines and used traction motors rather than hydraulics, it was innovative but was soon outdated.

BR chose Class 47s instead. Falcon was withdrawn in 1975 and scrapped a year later.

D0260 (Lion)

Lion was a diesel-electric prototype locomotive built in 1962. It was a collaboration between Birmingham Railway Carriage and Wagon Company, Sulzer, and AEI. It was created to test new traction tech and had a Co-Co wheel setup for improved grip.

BR tested the Lion extensively, running services from London Paddington to Wolverhampton and later from London King’s Cross to Finsbury Park. If you were around at the time, you might remember it for its distinctive white paint, gold stripes, and fibreglass roof panels.

Lion was withdrawn from service in 1964 and scrapped a year later.

DP1 (Deltic)

DP1, better known as Deltic, was a groundbreaking 3,300-horsepower demonstrator locomotive built in 1955. This train used two Napier Deltic engines, combining high power with low axle load.

Although initially rejected, 22 locomotives were eventually built between 1961 and 1962 to replace steam on express routes like the Flying Scotsman and to introduce the first regular 100 mph services.

Deltic was withdrawn in 1961, it now resides at the National Railway Museum.

GT3

The GT3 (Gas Turbine 3) was a prototype gas turbine locomotive built in 1961 by English Electric. It produced 2,750 horsepower and resembled a steam engine in both design and livery. It was nicknamed ‘The Chocolate Zephyr.’

Despite rigorous testing, development proved to be costly, this led to its eventual withdrawal and scrapping.

There are no preserved models, but you can see the designer's notes in the National Railway Museum Archives.

HS400

The HS4000 Kestrel was a 1967 prototype diesel locomotive built by Brush Traction. Designed to promote low-maintenance, single-engine performance during a twin-engine era, it packed an impressive 4,000 horsepower from its Sulzer 16LVA24 engine. This was enough to haul a 2,000-ton coal train solo.

It also ran express services between King’s Cross and Newcastle.

Despite its power, it exceeded British Rail's 20-ton axle load limit. Engineers tried to reduce the weight by fitting new bogies, however, they didn't succeed.

In 1971, Brush sold the HS4000 to the Soviet Union for £127,000. It influenced Eastern European rail design, however, no examples survive today.

Yorkshire Engine Company Janus

The Janus was a  0-6-0 diesel-electric shunter built from 1956, it featured two Rolls-Royce C6SFL diesel engines, both with their own cooling and generating system. Initially, they could achieve up to a combined 400 horsepower. Later versions used Cummins engines for more power.

YEC built 102 Janus units; these mostly were used within the British steel industry, though some were exported.

Many Janus units went to scrap, although heritage railways like Cottesmore and Appleby have preserved models you can view.

Channel Tunnel

Trains running in the Eurotunnel must follow strict safety rules and operate both British and French railway networks.

Here’s a look of some of the unique locomotives used in the Channel Tunnel.

Class 0001

The five Class 0001 locomotives are 1,270 bhp diesel-electric trains built by Maschinenbau Kiel which are used for rescue and service duties in the tunnel.

When they're in the UK, they are listed under Class 21.

Class 22

The Class 22 were French SNCF Class BB 22200 electrics temporarily used in the Tunnel before Class 92s were ready.

Class 22s are dual voltage (1500 V DC and 25 kV AC), achieve an output of 5,600 KW power, and have a top speed of 160 km/h.

They're no longer in service in the UK, but you can spot them operating on domestic routes in France.

Class 9000

The Euroshuttle Locomotive Consortium (ESCL) was a partnership between Brush Traction and ABB. They built all 58 of the Class 9000 electric locomotives between 1993 and 2002.

These trains exclusively operate the road vehicle service through the Channel Tunnel. They can reach a top speed of 160 km/h and have an impressive axle load limit of 22.5 tonnes.

One unit, the 9030, sustained damage beyond repair in the 1996 Channel Tunnel fire; it was scrapped a year later.

You’ll get a chance to ride Class 9000s by taking the LeShuttle service through the Tunnel.

Departmental

Departmental locomotives handle maintenance and engineering tasks, not passenger or freight services. After British Rail introduced the TOPS system, two main departmental classes were defined.

Class 97

Covers a range of special-purpose or converted locos. Highlights include:

• 97201 'Experiment': Former Class 24, now preserved.
• 97250–97252 ('ETHELs'): Mobile generators (ETHELs), now scrapped.
• 97650–97654:Diesel shunters.
• 97701–97710: Battery units converted from Class 501 EMUs
• 97803: Lowered cab for Ryde Tunnel, now preserved.

Class 97-6

The Class 97/6 locomotives were a small group of five 0-6-0 diesel-electric shunters from Ruston & Hornsby which were used in BR’s Western Region. It featured detachable motors for towing at high speeds.

Three are preserved today at Lincolnshire Wolds, Swindon and Cricklade Railway and Heritage Shunters Trust.

Gas turbine

Before diesel took over, BR tried gas turbines. You've already read about the GT3 - here are the two gas earlier experiments.

18100

Metropolitan-Vickers in Manchester built the 18100 loco in 1951 for the Great Western Railway (GWR). This prototype featured 3,000 horsepower and ran an express service to London Paddington.

The 18100 was withdrawn in 1958 and was later rebuilt into Class 80 electric.

18000

The BR 18000 was a 1949 gas turbine from the Swiss manufacturer Brown Boveri. This prototype also featured a 2,500 horsepower turbine with a top speed of 90mph.

At the end of 1960, the 18000 was withdrawn from operation. It is now preserved at Didcot Railway Centre.

Petrol: Class Y11

Built by Simplex, the Y11 was a group of three petrol-powered locomotives. Each locomotive used a Dorman 4JO petrol engine, but delivered just 24 horsepower to the rails.

These tiny locomotives handled yard shunting as their 0-4-0 wheel alignment gave them great traction, vital for the type of jobs the operators needed them for.

All three Y11 locomotives were withdrawn and none have been preserved.

Steam: Class 98

The British Rail Class 98 classification covers all steam engines on the UK mainline. After the steam era, BR retained three in Wales - these were the only steam locomotives to ever to use BR's double arrow logo and corporate blue.

Since 1971, Class 98 is also used for privately owned steam locomotives registered to run on the mainline.

Class 99

This might surprise you, but 'Class 99' was originally used to classify train ferries that carried rail vehicles between Britain and mainland Europe under the TOPS system.

Today, however, Class 99 refers to a new fleet of dual-mode electro-diesel locomotives. These modern Class 99s are capable of hauling freight on both electrified and non-electrified lines, reaching speeds of up to 75 mph.

Unbuilt trains

Just like concept cars, there are concept trains, too.

Some ideas that didn’t get past the drawing board are:

• Class 18: A modern Type 1 shunter.
• Class 38: A planned freight locomotive that lost out to the class 60.
• Class 51: Known as the proposed 'Super Deltic,' Class 51s would have been the successors to the Class 50 and Class 55 locomotives.
• Class 88: Electric version of Class 58.
• Class 93: This proposed electric locomotive was intended for the West Coast Main Line as part of the InterCity 250 project.

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