The Fan Bay Deep Shelter was carved out of chalk in just 100 days in the 1940s as part of Dover’s connected offensive and defensive gun batteries, aimed at foiling German shipping movements in the Channel.
Lying 75ft below the Kent coastline, the 3,500 sq ft of interconnecting tunnels, which are reinforced with iron girders and metal sheeting, accommodated four officers and up to 185 men during the war.
The shelter – which was personally inspected by Churchill in 1941 – was decommissioned in the 1950s before being filled in with rubble and soil and abandoned during the 1970s.
Officials at the National Trust said the tunnels were a “time capsule”, giving fascinating insights into war-time life, with graffiti-covered walls, discarded ammunition and even a pools coupon found in the depths.
Following their rediscovery, 100 tonnes of rubble and soil were removed by hand in a project involving more than 50 volunteers, archaeologists, mine consultants, engineers and a geologist.
After remaining bricked up for more than 40 years, the tunnels open to the public today following an 18-month project and 3,000 man hours.
Jon Barker, visitor experience manager at the White Cliffs, said: “This rediscovered piece of the country’s Second World War heritage is a truly remarkable find. There has been no public access to the tunnels for over 40 years and so they remain much as they were when they were abandoned.
“We’ve carried out extensive conservation work to preserve both the natural decay and authentic atmosphere of the space.”
The shelter was carved out of the chalk by Royal Engineers from the 172nd Tunnelling Company and had a hospital, secure store and five large chambers providing bomb proof accommodation.
Behind the heavy security doors and the 125 steps descending to the tunnels, lie poignant reminders of its war-time history. Etched into the chalk is a large amount of graffiti, including names of military personnel, coarse inscriptions and an intricate 3D face of a young man, possibly a portrait.
Some of the inscriptions are accompanied by the regiment of soldiers, most notably from the Royal Engineers.
1941 is the most popular date which features alongside the signatures.
Written in chalk on a steel shuttering alongside where a bunk bed once stood is the phrase “Russia bleeds whilst Britain blanco’s” – a popular slogan adopted by disaffected soldiers.
Other finds included pieces of wire twisted into home-made hooks by soldiers to hang their uniforms, and a Unity Pools football coupon dated 20 February 1943, recording 14 football matches.
One of the first discoveries made by volunteers when they entered the tunnels was of a needle and thread, believed to be khaki wool, tucked into the tunnel wall.
And bullets, including British .303 cartridges and American 30-calibre ammunition rounds, were found throughout the tunnels, often tucked into small gaps in metal sheeting.
Two rare First World War sound mirrors also form part of the site.
Regarded as one of the first early warning devices invented in the UK, sound mirrors gave advanced notice of approaching enemy aircraft but became obsolete with the invention of radar technology in the 1930s.
White Cliffs volunteer Gordon Wise said: “Seeing the tunnels in their raw state when they were first discovered, handling artefacts and giving tours is like standing in the footsteps of history.”