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Bugging the Nazis in World War II

Helen Fry

In 1939 British intelligence took over Trent Park in North London, the former country house of the aristocrat Sir Philip Sassoon. The house was “wired for sound,” and a hidden workforce of men and women moved in. This was one of three secret sites where German prisoners, and later Hitler’s generals, were held to try to surreptitiously gain intelligence from them. The whole deception was centered on microphones hidden in the house.

Didn’t the German prisoners ever find the microphones? It is a question that I am frequently asked. An interesting early transcript has emerged of a bugged conversation between three German U-boat prisoners. It does not give the prisoners’ names but designates them N.209, N.210, and N.184. It was January 1940:

Prisoner N 209 bangs on the wall to gain the attention of N 184 in the next room. “We have a microphone in our room,” he says, “built in above the fireplace. I unscrewed the lid.”

Meanwhile another prisoner (N.210) tries signalling his name to N.184 by tapping on the wall. N.184 implores him to come closer to the wall so they can talk:

“They have microphones in here after all,” he says.

The transcript of the bugged conversation then adds in brackets:

Begins to knock on the walls to find the microphone.

There is no evidence that the prisoners had actually found the device. The guard came running into the room and disrupted the conversation. The irony of this incident is that their actions and comments were all being overheard and recorded via the microphones hidden in the light fittings and fireplaces in the rooms. The microphones were wired to the “M Room” (M for miked) in the basement of the house. The game would have been up if prisoners had found the devices. Intelligence was needed to win this war—a war that Germany could have won if the new technology and secret weapons at secret sites in Germany had not been discovered by the Allies through this elaborate operation. The Allies were subsequently able to destroy Germany’s experimental weapon sites as well as the launch sites for the V-1 and V-2. The security-conscious prisoner was moved to another camp to avoid rumours spreading about microphones.

Seventy-five years later, working as the official historian at Trent Park during the transformation into a museum, I can understand why the German prisoners, and later Hitler’s captured generals, never found a single microphone. All the original WWII wiring has been discovered in the house. It is so deeply embedded in hollow spaces behind elegant panels and in the walls of the sitting rooms, throughout the bedrooms and behind skirting boards, that unless a German general had smashed the panelled walls or prized away the skirting boards, there was no way the microphones could be found. The microphones had long since gone to protect the secrecy of the wartime operation. 

When shown the largest bedroom on the first floor, the site manager says: “Whoever was in this room must have been important because it is the most heavily bugged room in the whole house. Microphones every one meter!”

This was probably the bedroom for General von Arnim, the commander who surrendered in North Africa in May 1943 with 350,000 men. The other generals would have sat around the fireplace in his room for discussions because he was appointed by them as their camp leader while at Trent Park.

Today, in a deep cavity in the bathroom behind his bedroom was found the main artery of the whole bugging operation. The original wires are connected in hidden cavities and false ceilings down to the ground floor stately rooms, behind skirting boards and every fireplace. The special lead-lined wires go down into the basement. There are thousands of meters of wiring from the attic, to the second and first floors, to the ground floor into the basement and feeding to the far end. It all ends at the three “M Rooms”—the listening rooms that had special recording equipment.

With these “archaeological” findings, it is possible to understand exactly how the physical wartime operation worked. The microphones may have gone, but small hollowed gaps exist in the skirting boards where they once were. The gaps were found today with bits of old newspaper plugged in them from the 1970s. During any work over the last few decades, it is unlikely that anyone knew what the gaps were for and plugged them.

The whole bugging operation was an extraordinarily clever deception against Nazi Germany. It resulted in the British and American intelligence services holding fifty-nine German generals in the house plus forty senior German officers captured from the battlefields of North Africa and Europe. To ensure they kept talking and stayed relaxed, the generals were treated according to their status as “military gentlemen” and wined and dined. It included elaborate lunches at posh restaurants in central London to pamper to their egos and self-importance. The aim was to relax them enough so they would talk freely within earshot of the microphones. It worked. Unlike prisoner N.209, they never suspected the microphones—as demonstrated by a letter written to Captain Hamley, one of the British interpreters at Trent Park, on his retirement from Field Marshal Gerd von Rundstedt, who is being held in the house. It is dated September 1945:

We all regret your departure very much! You have never seen in us the victims of a mis-directed policy, the enemy, but always the human beings. . . . [you] lighten the heavy burden of captivity for every one of us. . . . our sincerest wishes for your further welfare and assure you that we shall always preserve a true and grateful memory of you.

They were fooled to the end . . .

Helen Fry is the author of The London Cage and over twenty books focusing on intelligence and POWs in World War II. She consulted on the docudrama Spying on Hitler’s Army and appeared in BBC’s Home Front Heroes.

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