Tapping Hitler's Generals

During World War II probably all the belligerents listened-in secretly to their prisoners. The general rule seems to have been that the interrogation of selected prisoners was documented, but not the private conversations. Richard Overy has published the protocols of National Socialist leaders under interrogation in 1945–46.[16] Other trials were run by the United States, Great Britain, Germany and the Soviet Union.[17] As far as is known, it was the British who perfected eavesdropping as a method of intelligence gathering. At Farm Hall in Cambridgeshire, the conversations of the interned German nuclear physicists were secretly recorded in the attempt to discover how far Germany had advanced towards building an atomic bomb,[18] but the British did not disclose their practice of having listened-in systematically to selected prisoners of war for several years before that.

The British intelligence service began planning to use the method from the beginning of the war. On 26 October 1939, orders were given to set up the Combined Services Detailed Interrogation Centre. Initially under MI9, from December 1941 it fell within the ambit of the British Army’s newly formed MI19 Department at the War Office under Lt-Colonel A. R. Rawlinson. All reports originating at CSDIC were to be distributed to the three arms of service for collation with other information, e.g. signals intercepts and air reconnaissance photographs, to compose a specific intelligence picture.[19] The CSDIC organisation in England was complemented later by a centre in North Africa (CSDIC Middle East) and from the autumn of 1944 another in France/Germany run by the US Army (CSDIC West).

The UK interrogation centre had modest beginnings: in September 1939, only six officers (three Army, two RAF and one RN) had been appointed to question German prisoners at the Tower of London. In December that year the centre was relocated to Trent Park, a large mansion with extensive grounds near Cockfosters, north of London. German prisoners of war–in the early years a manageable number of Luftwaffe and Kriegsmarine men–together with Italian prisoners were ‘pre-sorted’ in transit camps by the PoW Department and those believed to have important knowledge were sent to Trent Park for comprehensive questioning and the secret monitoring of their conversations.

CSDIC (UK) used a variety of refined tricks to tap the required knowledge. ‘Cooperative’ prisoners and German exiles were used as stool pigeons to get conversations moving along the desired track[20] while prisoners of equal rank but from different units or arms of service would be bunched together. This method paid off: U-boat men would air their experiences at length, airmen would explain the technology of their aircraft and combat tactics in great detail to naval comrades. Army men arrived at Trent Park relatively quickly after capture–from a few days to a couple of weeks. They would often still be suffering the dramatic effects of their capture, perhaps having narrowly escaped death–and would be anxious to talk about their experiences.

On 5 October 1940 it was decided to increase CSDIC (UK) staffing levels to enable two camps to be run simultaneously. Trent Park could house only a limited number of prisoners and space for the constantly growing number of assessors was inadequate. It was also considered prudent to have two centres in order to reduce the risk of losing everything in a Luftwaffe air raid.

On 15 July 1942 CSDIC (UK) moved with its entire staff into the new interrogation centre at Latimer House at Chesham, Buckinghamshire (No. 1 Distribution Centre) with a maximum capacity of 204 prisoners. On 13 December a second new centre ten miles away at Wilton Park, Beaconsfield (No. 2 Distribution Centre) was opened with room for 142 prisoners, mainly Italians.[21]

The opening of the two new institutions allowed Trent Park to be converted into a long-term centre for German Staff officers. In the relaxed atmosphere it was hoped that its high-ranking population would reveal secrets in their private discussions.[22] The first new prisoner was General Ludwig Crüwell. He had been captured in North Africa on 29 May 1942 and arrived at Trent Park on 26 August after a long sea voyage. He was joined on 20 November 1942 by General Wilhelm Ritter von Thoma, a prisoner of the British for the previous two weeks.