A secret Second World War bunker built on the orders of Winston Churchill lay hidden under a Thorpe St Andrew estate for almost 70 years.
Its entrance is behind a bookcase, its aerial was disguised in a tree with the feeder cable under the bark, and there was an escape tunnel in case its operatives were discovered.
Now the underground wireless station, on private land at Pinebanks, off Yarmouth Road, has been protected as a scheduled monument by the government on the advice of Historic England.
The rare IN-Station, also known as a Zero Station, was part of a mysterious secret wireless network operated mostly by civilian agents.
Wireless stations were set up in 1940 by Winston Churchill in response to the increasing threat of German invasion.
It is thought that just 32 of the bunkers were built in England during the Second World War, with just a dozen discovered so far and the Pinebanks bunker is one of the most intact examples.
The station, which received messages from OUT-Stations in enemy-occupied areas, was found by a retired groundsman in the gardens of Pinebanks in 2012.
It has now been awarded special protected status to preserve it and to celebrate its history.
Heritage minister David Evennett said: “This underground wireless station is a rare and unusual example of our Second World War heritage and deserves to be protected.
“It is a reminder too of the often forgotten role so many civilians played in the war effort often acting in secret and undercover.”
The recruits in Churchill’s Secret Army, also known as the British Resistance Organisation, had to verbally swear to secrecy, with one hand on a Bible. In some cases even their families knew nothing of the role that required them to leave their homes regularly at night.
Historic England’s Tony Calladine said: “This amazing place that has survived intact played a highly secret but vitally important role in preparing us for a feared invasion during the Second World War. Because so much information about the stations was either hidden or destroyed, this small but significant dugout has great potential to teach us about a relatively little-known area of our 20th century military history.”
A spokesman for Ocubis Ltd, development manager for site owner Berliet Ltd, said: “We have been liaising with BDC and Historic England and, as we have always stated, will ensure the setting of this historically important former Norwich WW2 IN-station in Thorpe St Andrew is preserved.”
It is thought that the bunker was built under the Jarrold family’s tennis court at Pinebanks in the 1940s.
Details only emerged after the family’s former gardener, who had to sign the Official Secrets Act, told a young groundsman about the construction work he had witnessed.
The gardener did not disclose this until after his retirement, and he did not reveal the location, with this emerging later.
Winston Churchill had set up a secret army unit called GHQ Auxillary Units with a particular branch known as Special Duties, and wireless stations were built as part of this.
Civilian volunteers living in the most threatened coastal areas of the country were trained to spy and report on German military activities from within occupied areas, with their messages received by IN-Stations like the one at Pinebanks.
Details about their locations and construction were kept secret and very little documentation of the stations exists.
Information was protected in case they should be needed again in the future.
Historic England is asking the public to come forward with information about family members who were trained to be civilian spies, or any clues as to where the remaining 20 IN-stations lay hidden.
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