A hidden tunnel complex that formed Britain's first line of defence in World War II opened to the public this week after six decades buried as a forgotten time capsule.

The underground labyrinth is inside the White Cliffs of Dover, an iconic symbol of England on its southeastern tip and a natural coastal defence at the closest point to continental Europe.

Standing at the clifftop entrance, tour guide Gordon Wise looked across the busy Channel.

"You can actually see France, 21 miles (34 kilometres) away, just 70 seconds flying time for a shell," he said as he surveyed the lights, buildings and beaches visible on the other side.

"You get some idea that this was really the frontline. This was where the defence of Britain had to start."

The tunnel network, 75 feet (23 metres) down inside the chalk cliffs, supported the 185 troops and their four officers who manned three gun batteries and slept in bunks.

The digging began after prime minister Winston Churchill visited Dover in July 1940 and was enraged to see enemy German ships sailing unopposed through the straits between Britain and Nazi-occupied France.

The Fan Bay Deep Shelter tunnels were constructed within 100 days.

The 3,500 square feet (325 square metres) of tunnels were abandoned in the 1950s and filled in with debris in the 1970s. Only a metal cover plate on the grassy clifftop gave any clue as to what lay beneath.

- Trap door into the past -

The National Trust conservation body rediscovered the shelter after purchasing this section of the cherished cliffs in 2012, and began a mission to revive the tunnels.

Fifty volunteers -- Wise among them -- spent 3,000 hours over 18 months removing by hand the 100 tonnes of rubble tipped down the surface entrance.

"It's an important piece of wartime heritage and it's also a piece of forgotten history," said Jon Barker, the site's project manager.

"The story of the cross-Channel guns was largely forgotten," he told AFP.

Some 125 steps down, the tunnels are damp with condensation due to the moist, warm summer air. They smell of the creosote on the wooden support beams.

The tunnels are lined with rusting corrugated steel arching, some of which was removed for scrap in the 1950s, revealing the fossil-filled pristine white chalk behind it.

The temperature remains a cool 54 degrees Fahrenheit (12 degrees Celsius) all year round.

"Today the tunnels are abandoned, they feel quite spacious and they're very quiet," said Barker.

"But during the 1940s, it would have been an extremely busy place. It would have been quite hot, noisy and smelly."

- Saucy graffiti -

The project's volunteers found abundant traces of the long forgotten soldiers' lives.

Cigarette packets, telegrams, improvised clothes hooks, football betting coupons and rifle rounds were discovered, while a copy of "The Shadow on the Quarterdeck," a 1903 raunchy naval adventure, had been stashed on top of an air duct.

The chalk walls are etched with graffiti, usually the names of troops, such as "Nobby Clark 7/11/42."

Elsewhere there is a game of noughts and crosses, a tiny carved face, and some bawdy graffiti on bricks from the latrines, making light of the lack of toilet paper.

"Parade is due I dare not linger / here goes I'll use my finger," reads one example.

Later graffiti carvers left their mark, including adventurous cavers and locals. "Nick and Julie" snuck inside for many enjoyable visits in the 1970s.

"It was very difficult and dangerous to get in. Because of that, it's kept the tunnels in fantastic condition, which is why they're a time capsule from the 1940s," said Barker.

The dig also uncovered two rare World War I acoustic mirrors built into the cliff face.

Before the advent of radar, the 15-foot (4.6-metre) diameter concave sculptures concentrated sound waves and gave an early warning on the direction of incoming aircraft, shipping and enemy fire.

Hosted by volunteer enthusiasts, a torchlit guided visit down the tunnels costs £10 ($15.50, 14 euros).

Telephones from the 1940s connect the shelter to the surface. The handset in the tunnel suddenly rings and a jovial volunteer answers, "Hello? Winston?"
Source: AFP