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As German tanks rolled over the border and occupied Poland on 1 September 1939, one of Britain's most senior spymasters, MI6 intelligence officer Thomas Joseph Kendrick, arrived at the Tower of London to open a unit that would secretly bug the conversations of German prisoners of war. Here, the prisoners gave nothing away in interrogation, but when returned to their comrades they began to boast about what they had not revealed. Little did they realise that the light fittings and fireplaces had hidden microphones, supplied by the Radio Corporation of America (RCA), which were wired to a secret listening room. So successful was the operation that Kendrick requisitioned the large country estate of Trent Park at Cockfosters in North London and 'wired it for sound' for Axis prisoners captured from 1940. The volume of intelligence gathered was staggering: from intelligence ahead of the Battle of Britain in 1940 and new enemy technology to night fighter strategy, new aircraft and fighting capability, U-boat operations and construction, German campaigns on the Russian front, detailed information on coastal defences, their construction and enemy operations ahead of D-Day. Crucially, too, they amassed details of the concentration camps as well as admissions from the prisoners about Hitler's annihilation of European Jewry.
Within two weeks of the bombing of Pearl Harbor in December 1941, American intelligence officers arrived at Trent Park. They were from the USAAF, the US Navy and Army, and the Office for Strategic Services (OSS, the forerunner of the CIA), and would make an essential contribution to this clandestine operation based in Britain. They were assigned to the interrogation of prisoners and 'befriending' of Hitler's generals after capture on the battlefields of North Africa and later during the D-Day landings, the Normandy and Ardennes campaigns. By now the microphones at Trent Park were embedded deep in the walls, behind skirting boards, under floorboards, in plant pots, the billiards table and even the trees in the garden. The Generals were wined and dined, looked after by a fake aristocrat 'Lord Aberfeldy' (intelligence officer Ian Munro) and taken on day trips. Their favourite excursion was to the Ritz Hotel in central London where they were given copious supplies of gin and good food. This frivolity and outlandish treatment had one aim – to win the intelligence war. It led to the Generals inadvertently giving away Hitler's secret weapon and atomic bomb programmes as well as shocking details of the concentration camps.
Kendrick opened two further bugging sites at Latimer House and Wilton Park, some 20 miles from London, again with US intelligence personnel, to process 10,000 lower rank prisoners. His staff continued to provide intelligence that fed into every campaign of the war: masses of information that impacted on the devastating U-boat attacks on transatlantic Allied shipping and the wider Battle of the Atlantic. The intelligence also yielded a vast array of material on new German weapons that demonstrated Nazi Germany's determination to win the tech war, and campaigns after D-Day, including the Ardennes campaign. Information on mass atrocities and concentration camps in bugged conversations from 1943 became increasingly more detailed and graphic, providing a clear picture of precisely how the Nazi war machine was murdering Europe's Jews in their millions.
Several hundred American officers received instruction at Kendrick's unit, and went on to serve in American mobile intelligence units. In June 1942, Lieutenant-Colonel W. Stull Holt of the United States Army Air Force (USAAF) was appointed to command the American presence at both Latimer House and Wilton Park. Other US personnel, including from the FBI in Washington, passed through the sites for special intelligence training by Kendrick's officers for anything from two weeks to two months. In August 1942, Mr Witney Shepardson and Mr Maddox of the OSS came on a special visit to Latimer House from America. After this visit, a special British intelligence committee ruled that copies of all transcripts emanating from the 'M Room' should now be circulated with American intelligence, and copies sent to Washington. The following month, Mr H M Kimball of the FBI made a transatlantic visit to Latimer to see the work at first hand. Kendrick impressed Kimball with the highly efficient nature of the covert work. A grateful J Edgar Hoover, head of the FBI, wrote a personal letter of thanks to Kendrick afterwards.
The following twelve months saw a number of visits from personnel of the US army to Latimer and Wilton Park, including Brigadier-General Kroner (Chief of Military Intelligence Section, USA), Cdr Riheldaffer (US Navy) from Fort Hunt, and Colonel Catesby-Jones (POW department, Washington). In October 1942, the US Air Force joined the air intelligence section at Latimer House which was under the command of Denys Felkin. Felkin later wrote: 'A successful fusion of the RAF and USAAF air interrogation was founded. This cooperation was maintained with the highest measure of success until well after the closure of the war.'
American intelligence officer Heimwarth Jestin soon joined Kendrick's sites. Jestin was originally attached to the US 169th Infantry Regiment, 43rd Division and, after several training postings within the United States, he was sent to Fort Ritchie at Cascade, Maryland where officers received in-depth training in interrogation and intelligence work. Then in February 1943 he received orders for an overseas transfer to England for hush-hush work. Under the cover-name 'Lieutenant Colonel Jenkins', he interrogated special prisoners. He recalled in his private memoirs: 'We were vetted in regard to language usage, technique, and ability to understand the prisoners we talked to. It was a thorough and careful training.' Once in the United Kingdom, he found himself interrogating German prisoners of the Afrika Korps, captured in North Africa in 1943. He later said that: 'the interrogation was more exacting, for these prisoners were, on the whole, intelligent and unwilling to disclose information.' Jenkins was posted from Latimer House to Wilton Park for the remainder of the war. Here, he interrogated German generals captured on the battlefields of Normandy after D-Day, and before their transfer to Trent Park. His work was so important that the British honoured him with a medal – the OBE. Commanding Officer Kendrick provided valuable training to OSS officers and was honoured with the Legion of Merit by Edgar Hoover in 1947.
The 'theatrical stage set' with the Generals at Trent Park in particular could not have been created better as fiction. Fortunately, the 'mad hatters tea party' of daily life at Trent Park has been recorded in the weekly intelligence reports and the transcripts of conversations – now available to historians. These preserve rare real conversations of the war and an unprecedentedly unique snapshot into daily life in the Second World War. And therein lies the extraordinary gem. This was no fiction, but one of the greatest deceptions against Nazi Germany of the Second World War and one in which the early American Secret Service played a vital role. But it would be 65 years before any whisper of these secrets finally came out and only after 75,000 files were released into the National Archives in the United Kingdom and America.
Today, Trent Park is set to become a national museum to this secret war and the bugging operation. The American contribution will be part of the interpretation and story there. As soon as funds have been secured, the ground floor and basement of the mansion house at Trent Park will open as the museum in 2022. More information on the American personnel and this history is needed to do justice to the American wartime contribution. If you have information and photographs, please contact Helen on: www.helen-fry.com. For more information on developments with Trent Park Museum, see trentparkmuseum.org.uk
Historian Helen Fry is the author of The Walls Have Ears: The Greatest Intelligence Operation of WWII (Yale:Sept 2019) She writes occassionally for The Wall Street Journal