The Secret Factories Hidden Beneath Britain While the War Raged Above

The Secret Factories Hidden Beneath Britain While the War Raged Above

Today I want to discover more about the extraordinary underground world created across wartime Britain. As bombing threatened factories, military sites and supply depots, the government increasingly looked below ground for protection. Old quarries were converted, new tunnels were excavated and important parts of Britain’s war effort were hidden beneath layers of rock.

Betty Turner and another worker carrying out factory work underground, probably Spring Quarry, Corsham, Wiltshire, 1942. Credit: Wikimedia Commons, Public Domain

One of the most remarkable examples could be found around Corsham in Wiltshire, where generations of Bath stone quarrying had already created a vast underground landscape. By 1940, more than 60 miles of tunnels stretched beneath roughly 3,000 acres of countryside, generally around 80 to 100 feet below the surface.

Workers receiving instructions at a workbench inside an underground factory, probably Spring Quarry, Corsham, Wiltshire, 1942. Credit: Wikimedia Commons, Public Domain.

One of the most important sites was Tunnel Quarry, which the War Office acquired before the war and converted into a huge underground ammunition depot. This was far more sophisticated than simply stacking explosives inside an old quarry. There were underground railway platforms, conveyors, lifts, ventilation systems, communications equipment and power facilities. By June 1944, more than 10,000 tons of ammunition were being moved through Tunnel Quarry every week.

Workers clearing stone from the old quarry during its conversion into an underground factory, probably Spring Quarry, Corsham, Wiltshire, 1942. Credit: Wikimedia Commons, Public Domain.

But how do you hide something on that scale?

Thousands of workers had been involved in preparing the underground sites, while military personnel, railway traffic and supplies became increasingly visible. Local people could hardly fail to realise that something unusual was happening.

One explanation allowed to circulate was that the Ministry of Food was creating an emergency food store underground. It sounded believable enough, but later recollections suggest many locals knew, or at least strongly suspected, that it was not the truth. The aircraft factory and what some simply called “the dump” appear to have been fairly well known locally, even if the full scale of the operation was not.

Corsham contained a lot more than ammunition. After the Bristol Aeroplane Company’s works at Filton were badly bombed in September 1940, the government became increasingly worried about the vulnerability of aircraft production. Spring Quarry was chosen for a huge underground aircraft-engine factory.

Transforming an old quarry into a modern factory was hugely difficult. Rubble had to be removed, floors levelled, roofs strengthened and electricity and ventilation installed. Lifts and even escalators were provided to move workers between the underground complex and the surface.

Spring Quarry never became quite the vast production centre originally imagined. Construction took longer and cost more than expected, and by the time much of it was ready, the immediate bombing threat had reduced. Aircraft-related work did take place underground, but on a smaller scale than first planned.

Other Corsham quarries had completely different roles. Clubhouse Quarry was used by De La Rue to store replacement currency for occupied European countries, while other underground spaces were used for military storage and headquarters.

And Wiltshire was not alone.

At Drakelow in Worcestershire, tunnels were excavated into sandstone from 1941 to create an underground factory connected with aircraft-engine production. By 1943, Rover was carrying out work there as part of the wartime shadow-factory programme, while unused parts of the complex were used by the RAF for storage.

These underground sites were not easier places to work. They brought problems with ventilation, damp, lighting and transport. But that was not the point. They existed because factories, ammunition and essential services hidden beneath layers of rock were far harder to destroy from the air.

I keep wondering what it must have been like for people living nearby. They saw buses carrying workers towards guarded entrances, increased railway traffic and military personnel, but they may never have understood the true scale of the hidden world beneath them.

Above ground, wartime Britain carried on while, below it, another Britain was working in secret.

If you had lived nearby, do you think you would have believed the official story, or would you have worked out what was really happening underground?