A huge, little-known network of underground pipes spans the UK – officially still a state secret, and bringing fuel to the plane that takes you on holiday.

If you flew over it, you’d have no idea it was there.

One of the great British engineering projects of the 20th Century is completely hidden from view, traversing hundreds of miles across the country. There’s no trace of it except for a series of small holes on the tarmacs of the UK’s major airports, including London Heathrow.

As the video below shows, what lies beneath is a fuel network of colossal scale – one which carries aviation fuel from the refineries where it’s unloaded straight to the aircraft waiting to be topped up.

But it was created not with flights to far-flung destinations in mind, but the very survival of the UK. And the exact location of the network is still not publicly known.

The origins of this underground network date back to before World War Two. A secret pipeline was built between Liverpool’s Stanlow Refinery all the way to Bristol’s Avonmouth Docks and then fed into national road and rail distribution networks.

In September 1939, war broke out, and the need for a protected network became more pressing. As the war progressed and Germany occupied Holland, Belgium and France, Britain became more vulnerable to enemy bombers. There was also the need to send fuel from the western ports through to the airfields in the east of the UK.

But sending it via the roads and rail made the precious fuel far too vulnerable to aerial attack. The solution was to bury a pipeline – safe from enemy bombers.

The project – the Government Pipelines and Storage System (GPSS) – was carried out with the utmost secrecy; the pipeline channels were even dug at night so that enemy reconnaissance aircraft couldn’t see any interesting activity.

The network ended up being able to supply fuel to all of the airfields used by British and American bombers that carried out raids over Germany and occupied Europe, and was also used by the Allied armies that landed in France in June 1944, which was called Pluto (PipeLine Under The Ocean).

The end of World War Two did not see the end of the secret pipeline – in fact it was just the beginning.

As civil aviation took off, the pipelines were extended, ferrying fuel to new civilian airports as well as military airfields across the UK. Eventually, as the video by YouTuber Tom Scott shows above, it created a network spanning some 1,500 miles (2,400km).

In a few stretches, like the one Scott videos in Gloucestershire, the pipeline rises up out of the ground for a few metres, before plunging back under the surface again.

But officially, this network is still a state secret. That’s despite the fact that in 2015 the GPSS was sold to a Spanish company and is now known as the CLH Pipeline System. An approximate map of the pipeline can be seen in Scott’s video and on the CLH website, but the exact position has not been made public.

In many areas, it’s often only discreet warning posts – some of them dating back to World War Two – that warn farmers, builders and developers to proceed with caution. Drilling down into pipes full of high-pressure aviation fuel is something most of us would probably want to avoid…

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