Disbanding WCIU in September 1948 also removed what was left of Britain’s wartime interrogation system. That system had started as a few prison cells in the Tower of London, earmarked for the small number of German prisoners who were expected to be brought to Britain. It ended nine years later and only six miles away, in Kensington’s London District Cage, where some of the crimes of that war had been investigated. In the intervening years, Europe’s Jewry was almost completely wiped out; millions more were systematically targeted, dying in combat, during forced labour or by starvation, and others were simply murdered in their towns. Large parts of Europe were bombed out, economies were completely devastated, regimes had fallen and civil wars erupted.

As the reality of the conflict was unfolding, assumptions of what response it needed changed, as did beliefs about what individuals knew that could assist the war effort. This transformed the role of interrogation. The initial idea that a few cells in the Tower of London would suffice for an interrogation camp was abandoned very quickly. Dozens of sites – schools, mansions, racecourses – were repurposed in order to facilitate interrogation. Hundreds of thousands of people were caught up in those camps. This was, after all, a total war and so the people of interest to intelligence services spanned well beyond a few soldiers. The reach of the resulting interrogation system was vast and unprecedented, affecting every single prisoner of war, every refugee and every civilian who was believed to be in Britain clandestinely. All of these people underwent some kind of questioning. Most were sifted out, but a fraction were interrogated in detail on a broad spectrum of topics. Those select few were also the ones whose conversations were recorded. A similar process had to be repeated before anyone could leave the country, this time to ensure that no war criminals slipped through the net. Those believed to have either committed or witnessed war crimes were interrogated in detail and some of those also had their conversations recorded.

The nine-year history that the Tower and the Cage bookended was, as a result, far more compelling than one might expect of interrogation. It is a history neither of a mundane process nor, at the other extreme, of an activity that was by design sinister. It is instead a history of improvisation, of expertise, of unequal dynamics, of psychology and of the emotional charge of war. At its core, it is the history of how a process that was absent from Britain’s intelligence machinery in 1939 developed into one capable of producing a remarkable flow of information on different topics.

Certain broad conclusions emerge from the three case studies examined in this book, one being that interrogation was an important and central part of the wartime intelligence system. This is not because it was producing intelligence on a specific topic, but because it was in constant dialogue with various other parts of the intelligence machine. When it came to soldiers, their interrogations often refined information already known through signals intelligence, aerial photographs or mail censorship. This was precisely the aim. The ‘eyewitness’ angle that soldiers possessed helped to corroborate and explain what other sources could only hint at, ranging from timelines of events, descriptions of people, weapons and tactics, to living conditions across Europe and to Nazism as an ideology. It also worked in the opposite direction. When completely new intelligence came from interrogation, it would be up to other sources to investigate it. A vast amount of information was collected as a result and, as expertise expanded across the intelligence system, was either checked with other sources or stored for later use. When it came to spies, here too much was already known about them by the time they were held in Camp 020. Yet under interrogation, the Abwehr’s recruits would put real names to aliases, they would describe people and confirm cover addresses and codes, all of which helped to build a clearer picture of enemy espionage. This is therefore not a case of a hierarchy in which interrogation can be easily placed above or below sources such as signals, telegraphic and postal communications, photographic reconnaissance or agents in the field. When it came to war criminals, on the other hand, interrogations were absolutely vital. With Britain determined to pursue ‘show-off’ trials in Germany rather than true show trials, it was only through interrogation that evidence could be secured for successful prosecutions.

Spies, soldiers and war criminals did not produce comparable intelligence, but their interrogations did deliver. While we cannot easily isolate the pieces of information that were operationalised, what is clear is the fact that each camp extracted the intelligence it was asked to extract. Soldiers offered tactical, operational and strategic-level impressions, almost all spies confessed their missions and when suspected war criminals refused to recount their past actions to interrogators, witnesses did that for them. Even if it were possible to isolate the information that was actually used, judging interrogation’s value solely through that information would miss the point. What interrogation was fundamentally about was producing and sustaining a constantly updated body of knowledge that could be referred to whenever needed, even in another war; after all, a future war with Germany was widely regarded as a question of time, and so some of the intelligence was kept explicitly due to its long-term value. Indeed, that wartime body of knowledge was returned to when investigating crimes after the war. The success of interrogation can therefore not be separated from the successes of the intelligence system overall, which was producing a stream of information that was ‘so comprehensive, though never complete’ that it allowed interpretations drawn from it to be ‘generally correct’.¹

This information was the product of a process shaped entirely through improvisation. None of the operations in this book – those of Camp 020, CSDIC and WCIU – had any direct predecessors from which to draw lessons. Even WCIU, which came with six years of interrogation experience, did not have a direct predecessor dealing with the type of investigation that it embarked upon. At the core of this history is therefore improvisation. It all started with a strong suspicion that interrogation could be a useful intelligence-gathering activity and should be utilised more than in the past. Much of that confidence stemmed from a belief that concealed microphones would capture what was needed. And the belief did bear out in practice, but only in part. Interrogators were quick to realise that microphones would be an aid rather than a panacea. They saw that microphones needed to be part of a more deliberate process through which prisoners would first be selected before their conversations would be recorded. The idea that all prisoners should be screened – briefly interrogated – for selection was then applied to all non-British civilians escaping to Britain from the Continent, so that Camp 020 could focus on the few who were almost certainly working for the enemy. By the time war crimes had to be investigated, screening all prisoners who were in the country was a given. What started as an understandably naive operation in the Tower of London turned interrogation into a sophisticated process and a network of camps that was well-coordinated, thorough and useful in different ways.

Responsible for these improvisations were the staff attached to those camps, and who initially were amateurs. Some of their roles did not even have peacetime equivalents, especially those associated with operating the secret microphones and doing the secret listening. Even face-to-face interrogation was something of an unchartered territory for intelligence. But responsiveness to pressure and dedication turned them into experts. At the same time, precisely because interrogation is so heavily reliant on people, bias was always a concern, hence the initially clear division of labour in order to minimise bias and maintain secrecy. In the camps dealing with soldiers, secret listeners were not interrogators. Interrogators were not decision-makers. Much of the time they were not even told why they had to ask prisoners specific questions. Even in the case of spies, where MI5’s Robin Stephens was privy to other intelligence about the people he was handling, he was still not the sole arbiter of what would happen to them after interrogation. This division of labour was lost as soon as the war ended, with near-bankruptcy and demobilisation both underway. At that point, interrogators became translators, liaison officers, assistant legal advisers and almost coroners. Yet they still made an effort to handle individuals based on the evidence rather than their personal views. And thus, for all the wartime innovations that were introduced, interrogation was never perfected: the targets kept changing and improvisation remained necessary.

The deeply human dimension of interrogation brought with it the question of fallibility, which applied to all involved – prisoners and staff. The people working in these camps had their own attitudes and limitations. This was recognised at the time, and measures were put in place to ensure that intelligence was as untainted as it could be. These measures were on the whole effective, in that individual pieces of information were considered reliable, as were the overall assessments of whether a prisoner was being truthful. But there were biases that ran so deep that they were not recognised, and which we can now see. This applied to anything that concerned the Jewish people, be it Jews under interrogation or information about what was happening to Jews in Europe. That Jews agreed to work for the Abwehr as a way to escape occupied Europe was simply not an excuse Camp 020 could accept; they were just as contemptible as anyone else. The language used to describe them, particularly but not only by Stephens, is a strong reminder that antisemitism was a European, not just a German, phenomenon. In CSDIC, too, information about what was happening to Jews in Europe was being recorded but seems not have been joined up; it was instead part of the more generic effort to learn about ‘atrocities’, a catch-all term that made no distinction between different forms of violence and who they were targeting. This remained after the war. But at that point, it became part of a deliberate political decision for WCIU not to differentiate between victims – so long as they were of Allied nationality – and not to deal with crimes against humanity. It may be possible, if one chooses, to explain away what happened in each individual case. Camp 020, for instance, dealt with a small number of Jewish prisoners, while CSDIC was producing an enormous amount of intelligence, much of which was fragmented. Explaining away events is not possible when looking at both the information and attitudes that emerge from these different camps, and the war crimes trials policy Britain pursued after 1945. It is the combination that confirms Britain’s failure to grasp the extent and nature of mass murder and genocide as told by its own sources – as it started to unfold, as it was underway and after the fact.

Interrogation’s success depended upon the willingness of those being interrogated to cooperate. To persuade someone to lower their guard and share useful information – be it when talking to an interrogator or unwittingly – required certain conditions. As a result, interrogation processes were always underpinned by psychological manipulation. Take the most obvious case of soldiers and concealed microphones. The conditions in which microphones were used allowed CSDIC to exploit this technology to the fullest, specifically by using stool pigeons and ‘matey entertainment’ (favourable treatment) which coaxed prisoners to eventually open up. This ‘simulated kindness’, as it was called, was only one way in which psychology was exploited, however. Matey entertainment and the like were not even considered by Stephens in Camp 020, because those were not soldiers captured doing their job but civilians who chose to side with Nazi Germany. For them, psychology was used to demoralise and scare them into admitting all they knew. Matey entertainment was, for more obvious reasons, also not entertained when interrogating suspected war criminals. Instead, witnesses of war crimes made a substantial difference in supplying key evidence where the suspect was uncooperative.

Individual commandants determined much of the psychological atmosphere within each camp. For Stephens and Alexander Scotland, their behaviour during the war was on the borders of what was acceptable even by 1940s standards and even during conflict. In Camp 020, solitary confinement and threats were used to drill into prisoners that they could not fool their interrogators. In the London Cage, Scotland bullied some of the prisoners who disobeyed orders or lied, all under the guise of emulating German-style ‘discipline’. There is nothing in the archive to suggest that CSDIC’s Thomas Kendrick permitted even a trace of the practices associated with Stephens and Scotland.

Yet individual commandants did not determine everything. This is because no individual commandant was going unchecked by higher command, and higher command had reasons to wish humane treatment for all of these groups. With suspected spies in Camp 020, MI5’s primary concern was that coercion or outright violence were counterproductive and would lead to false intelligence. They were also accountable to the Home Secretary, who would have to answer for any scandals if they were to break out. For the soldiers in CSDIC, higher command was concerned that mistreatment of any kind risked reprisals against Allied prisoners. For WCIU’s conduct with war crimes suspects, higher command’s concern was bad publicity in Germany or a defence lawyer casting doubt over how his client’s confession was obtained. Indeed, while initially we may think that the level of secrecy surrounding these camps enabled mistreatment, the opposite was true: the desire to keep these camps secret acted as a counterweight to mistreatment. The effect of secrecy was instead that it created a number of additional questions, particularly what to do with someone once their interrogation in such a top-secret place was concluded. But it did not enable abuse, either by design or negligence. So while abusive practices did occur, and by the commandants no less, they affected a relatively small number of those under interrogation and were out of sync with the overall good standards that were kept in interrogation camps.

For all the intrigue involved in interrogation, the administrative dimension of this history is therefore consequential. Spies, soldiers and war criminals underwent a similar process of screening and interrogation, but each fell under a different administrative structure and, importantly, one that was always discernible. For CSDIC, there was never a doubt that this was a War Office organisation, even if it had permanent Air and Navy Sections stationed within it. For Camp 020, MI5 was certain that this was an MI5 institution, even if they had to liaise closely with the Home Office about it. The same went for the work of the post-war WCIU, which was part of the JAG’s Office, and hence of the War Office. Perhaps had Britain interrogated no one other than the people mentioned in this book, the importance of administration would not have been appreciated. But then Stephens was sent to the chaos that was post-war Germany to set up a successor of Camp 020 and CSDIC. There, he was left to his own devices, without much direction and without any inspections from higher command. Soon enough, both in order to elicit information and to take revenge, prisoners who were a combination of former Nazis and suspected communists were systematically mistreated in ways that fell short of physical beatings (and even those may have occurred).

This brings us back to the point that interrogation was not an insular process, but one that was firmly embedded into the rest of the intelligence apparatus. When interrogation was successful – as it was with spies, soldiers and war criminals – those successes rested heavily on the workings of the broader intelligence machine. It was the iterative process between the three interrogation units of this book and other sections and organisations that allowed interrogators to furnish information that was both useful and accurate. In contrast, when interrogation was either fruitless (as in the Tower of London in 1939) or abusive (as in post-war Germany), this too was a symptom of problems with the broader system, rather than an outlier case.

All of this proves that interrogation is not an abstract event nor is it isolated from other social and military developments. It is instead a complex, human process that reflects assumptions and attitudes of the time. When it is also well recorded, as in the cases studied here, it can provide a ‘first oral history’ of its time, told by individuals whose experiences are otherwise difficult to capture in any large numbers. The majority of the people in these camps were insignificant to Britain. Most of the soldiers that CSDIC interrogated were not distinguished or high-ranking officers. Most of those detained in Camp 020 were not professional spies. War crimes investigations relied much on soldiers denouncing each other and on witnesses recounting what they had experienced. These are not the figures we usually associate with intelligence work. Yet they are the protagonists of interrogation. To view interrogation only through its extremes, or only through the lens of torture, is therefore to overlook its real significance: that taken as a whole, interrogation reflects the deeper workings of the society that produced it.