In March 1940, Captain Alexander Scotland, a veteran intelligence officer of the Great War, arrived at the Hendon Aerodrome in London. Wearing the tunic that was given to him in 1915 when he joined the British Army, he was there to board a plane that would fly him to Arras in France. This was an unexpected turn of events. Until days prior, Scotland was resigned to the idea that there was no place for him in this war; it was up to ‘young England to do the fighting’, he told himself, after the War Office ignored his offer to lecture new recruits on the conduct of interrogation.¹ He was, after all, fifty-eight and had long retired from service. Then the War Office rang and ordered him to report to Hendon in uniform. Upon landing in Arras, he was taken to Dieppe, where he set up a ‘cage’, a term which in military nomenclature meant a holding camp for the purposes of interrogation.² His stay in Dieppe ended as abruptly as it began, however. Amid the panic caused by the rapid German advance in May, he threw himself and eighteen German prisoners of war onto two fishing boats, on which they reached England the next day. But his stint in this war was far from over. He was able to retire again only at the end of 1948, at the age of sixty-six and at the rank of lieutenant colonel.

The interrogation system Scotland became part of upon his return from France is the subject of this book. This system, which handled hundreds of thousands of prisoners of war, civilians and war crimes suspects, was in operation in Britain for nearly a decade. It was not the only system, in that interrogations were being conducted in active theatres of war, while in Britain itself there were also various establishments for vetting and brief questionings. In-depth interrogations, however, were the reserve of designated camps, and these are the places the book focuses on. Little interest was paid to them until the early 2000s, when historian Sönke Neitzel brought into the mainstream their most intriguing feature: the use of concealed microphones through which some prisoner conversations were recorded, transcribed and circulated to selected government departments.³ The role of interrogation in the war nevertheless remains ambiguous. Histories of interrogation do exist, but these have tended to focus on a single camp rather than the broader process of interrogation.⁴ Perhaps compared to other intelligence activities such as signals and espionage, interrogation might sound like a dull, perfunctory practice whose study may only be warranted when something goes wrong. And indeed, it is only when torture is proven or alleged that it attracts attention, potentially creating a flawed generalisation that interrogation is always a sinister practice.⁵

This book tells a different story. It uncovers a history in which interrogation became a valuable information-gathering method in the context of the Second World War, giving Britain remarkable knowledge of Nazi Germany in the process. Much of that knowledge, concerning individuals, armies, atrocities and numerous other subjects, could not have been gained through any other means in such depth. Not only was it obtained in interrogation camps, but it was also written down in an almost obsessively detailed way and so can be gleaned from tens of thousands of reports, indexes and verbatim transcripts of secretly recorded discussions. This was ‘mass observation’ of a different kind but no less revealing, for the topics Britain chose to focus upon tell us much about how it understood the war it was fighting. In many ways, the sources emanating from interrogation are a ‘first oral history’ of the Second World War.⁶ This is a term that David Cesarani used to describe the interviews of Allied psychologists with German soldiers – some of which had their origins in the interrogation camps studied here – but which is appropriate for much of the archival material that makes up this book.

What makes this history even more intriguing is how unlikely it was. When Neville Chamberlain told the public on 3 September 1939 that German troops had not withdrawn from Poland and that consequently Britain was now at war, there were not even trained interrogators in active service. Despite having been considered useful in the First World War, interrogation was not Britain’s primary source of human intelligence.⁷ The final year of that war – the point when Britain captured large numbers of German prisoners and systematically questioned them for order-of-battle intelligence, as well as to gauge their morale – had nevertheless left a conviction that interrogation must be exploited more in the future.⁸ The founding of the Royal Air Force in April 1918 must have also influenced this thinking, as it created a need for intelligence on a range of new topics pertaining to air power.

Another development that strengthened this thinking was the experience of using microphones to eavesdrop on prisoners, which seems to have happened almost by chance. In 1916, Britain scrambled to match the successes of the Germans and the French in tapping enemy communications, but ended up not benefitting much from wiretapping, which it abandoned by early 1918. The need to repurpose the technology it had developed may have been what sparked the idea to use it in prisoner camps instead.⁹ ‘Other uses to which the listening sets were put’, wrote a wireless officer in 1920, referring to the equipment used for tapping enemy messages, was in the prisoner cages for officers that were established behind the lines. ‘One of these sets would be fitted up with an ordinary telephone microphone, this being the piece you [speak] into while telephoning. This mouthpiece would be put up behind a picture or any other place where it could not be seen.’¹⁰ Another intelligence officer writing in 1920 made similar mention of the use of ‘listening sets’ in prisoner camps: ‘In order to hear what the Germans were saying among themselves and to one another’, he wrote, ‘listening sets, by which the human voice can be heard at a considerable distance, would be installed around the cage’. He explained that ‘the leads of these listening sets would be placed sticking up out of the earth in the very centre of the Germans, buried cables leading back to the listening operator’s hut outside the cage’.¹¹

The years after 1918 nevertheless saw the idea of developing interrogation wither. In the absence of a state of war, and of large numbers of prisoners to actually interrogate, systematic questioning for the purposes of gathering intelligence was abandoned, and so was the idea of developing microphones as an aid to this activity. Not only was it abandoned, but whenever the idea of using microphones resurfaced in the interwar years, usually in a policing context, it kept being dismissed. In 1922, the Chief Commissioner of the Metropolitan Police, upon being presented with a new listening device, emphasised that the usual practice was ‘listening outside a door slightly ajar, boring a hole through a partition, sitting in a cupboard or under a table’.¹² To be on the safe side, the police did purchase the device but a decade on were still asserting that ‘the ancient method of getting inside the cupboard generally works well enough’.¹³ Minds started to change in 1938, when the prospect of war led the government to consider new equipment for purchase. The Home Office, which was to hold demonstrations of how such a device could be used, received so many requests from interested departments that three sessions had to be held to accommodate everyone.

It was soon after those demonstrations, and after the Munich Agreement was signed, that the War Office began its search for an interrogation camp in which to install microphones and have it ready to operate as soon as war – which after years of appeasement efforts now looked inevitable – broke out. The Tower of London was confirmed as the best place in April 1939. Securing the premises was easier than finding the right people to run this operation, since the only ones who had some training were those who had fought the previous war. It is for this reason that people like Alexander Scotland were suddenly asked to put on their old uniform and report for service. Far from being a temporary solution, these veterans were kept in their positions for years, helping to turn interrogation into an invaluable part of the intelligence machine. The argument even went that, had the war broken out in 1949 instead of 1939, interrogation would have been much more limited because those veterans could not have influenced its development.¹⁴ Along with these veterans, interrogation was also comprised of ‘a sprinkling of experienced men from the Security Service and a few detectives seconded from police work’, as well as the women of the Auxiliary Territorial Service and refugees, most of them German and many of them Jewish.¹⁵

Interrogating Nazism is therefore first and foremost a book about the transformation of interrogation into a fully fledged and versatile process, one which elicited intelligence on multiple topics. These included information about different aspects of the German war effort – operations, tactics, morale, espionage – as well as evidence of war crimes that would shape the course of trials after 1945. Not all the information produced was useful, and even less of it was acted upon. Which pieces of information were operationalised is generally difficult to tell, even though illustrative examples are used throughout the book. In the case of soldiers, any information used had to first lose its origin in order to maintain the secrecy of the source, making it difficult for the historian to trace. In the case of spies, the use of relevant information often concerns the activities of the Secret Intelligence Service (SIS, or MI6) and thus remains classified. And when it comes to war criminals, we cannot know whether judges were directly influenced by information furnished by interrogators because their opinions were not written down. One thing is nevertheless certain: that interrogation camps were there, constantly producing an enormous amount of information which was perceived to be accurate and was ready to be used if and when needed.¹⁶ Indeed, what came to be considered as ‘intelligence’ in these camps demonstrates how elastic the term became, with interrogation establishments constantly evolving in order to capture it.

This flow of information was not natural. After all, the people in this book were not expected to want to share information with Britain. German soldiers, even when they disagreed with the Nazi regime, felt bound by a sense of military honour not to betray their oath and country. Although many of the German agents sent to Britain were not professional spies and so were not trained at evading questioning, they had a more pragmatic concern that anything incriminating they said would cost them their lives. War crimes suspects were also concerned that the price of talking would be a death sentence, and some tried to lie about who they were altogether. Unable to rely on a prisoner’s willingness to speak, interrogation necessitated an elaborate process, developed to elicit intelligence without prisoners realising what they were giving away. Microphones were at the heart of this process, but it was people who decided what to record and how to prime prisoners in order to share information that was worth recording. It was, in other words, the people overseeing this process who mastered the practice of interrogation on behalf of Britain. Interrogating Nazism is therefore also a book about a unique form of face-to-face interaction between the Axis and the Allies, all taking place on the British home front, which was a much more diverse and complex place than tends to be remembered.¹⁷

The people giving that intelligence were far from a homogeneous group. Many were committed Nazis; some were patriotic Germans; others were not even German; a small number were anti-Nazis; more were opportunists; and many more from across these different categories were anti-communists. Why were they all fighting for Hitler? Why were German soldiers not deserting, despite unfavourable odds? Why did they commit war crimes? Why were some French, Norwegians, Poles and Britons spying for Nazi Germany? Interrogation provided a first means to answer these profound questions, rendering Interrogating Nazism also a book about the role of ideology in this war, and specifically of how Nazism was perceived by Britain at the time.¹⁸

The story starts with those sent to Britain to spy, all of whom as far as we know were captured and interrogated by the Security Service (MI5). Not only were they captured, some were also ‘turned’ into double agents, feeding false intelligence back to Germany as part of the infamous ‘Double-Cross System’.¹⁹ It is those few – ten or so – who became double agents that we know something about, even though some 400 agents were arrested altogether, most of them nationals of Western Allied countries. What happened to them after capture? And what happened to the vast majority who were not used in deception operations? These are the questions answered in the first chapter, which looks at how MI5 interrogated these people in Camp 020 in Richmond, south-west London and uncovers how interrogation worked together with other intelligence activities – particularly signals intelligence – to frustrate the Abwehr’s rather pitiful attempts to infiltrate Britain. What is also a mystery is who the Abwehr chose for the ‘job’, and why people agreed to do it.²⁰ The second chapter uses the interrogation reports produced in Camp 020 to show that those who were sent as Nazi Germany’s spies proved to be quite different from those we might conventionally expect, and unlike the intriguing characters we tend to associate with intelligence activities more generally.

In far larger numbers imprisoned in the country were German soldiers.²¹ Of the over three million captured by Britain, almost all went through an interrogation system designed to identify those who held important intelligence. Those identified were sent to designated camps in Britain, part of a War Office organisation called the Combined Services Detailed Interrogation Centre (CSDIC, pronounced sizdik). This type of camp, whose work centred around concealed microphones, had no precedent. Yet in 1945, the Joint Intelligence Sub-Committee praised CSDIC for having provided invaluable operational, technical, economic and political intelligence. The third chapter looks at the processes that explain how this nascent organisation developed such an esteemed reputation. The intelligence sought is then the focus of the fourth chapter. Untangling the enormous paper trail produced by CSDIC in the UK shows the kind of information Britain valued, ranging from tactical intelligence to assist military operations, to scientific assessments of soldiers’ morale to prepare for the occupation of Germany.²²

Some of those prisoners were identified as suspected war criminals when the war ended. They were known as minor war criminals – concentration camp personnel, soldiers who tortured and murdered as well as their superiors who gave them the orders – in contrast to the ‘major’ decision-makers tried by Nuremberg’s International Military Tribunal, about whom much is known.²³ The final part of the book turns to these ‘minor’ war criminals, many of whom were interrogated on the very site in Kensington that today houses the Russian Embassy, and which at the time housed a camp known as the London District Cage. These were the final interrogations overseen by Alexander Scotland before he could retire again. The fifth chapter situates the role of interrogation in the policy landscape surrounding the war crimes trials, a landscape which was messy and politicised, and posed serious practical difficulties to interrogators who were faced with an unprecedented and thankless task.²⁴ The outcome of the resulting interrogations conducted by Scotland’s team – the War Crimes Interrogation Unit – between 1945 and 1948 is the focus of the sixth chapter. Drawing on the resulting interrogation reports, with both suspects and witnesses, the chapter shows the incredible difficulty of identifying suspects, the importance of witnesses and the emotional burden of these investigations on all involved.

The six chapters are divided into three parts, each dealing with a different category of prisoner – spies, soldiers and war criminals. This reflects the distinct institutional settings that governed the interrogation of each group. All of these people were questioned in depth, but they were questioned by different – albeit intertwined – bureaucracies, which were interested in very different things. For example, soldiers were usually interrogated on strategic-level intelligence, with little or no information recorded about them as individuals. In contrast, spies were questioned precisely in order to establish their true identity and motives. As a result, Chapter 4 on soldiers’ interrogation reports focuses more on the intelligence they gave, whereas Chapter 2 on spies’ interrogation reports focuses more on who those people were and why they agreed to spy for Nazi Germany. Each section, in other words, follows the logic of the material that each camp produced, allowing the book to reveal the diverse interests and priorities at work across Britain’s interrogation system.

The book, however, does not tell three disconnected histories of interrogation. It uses these cases to come to broader conclusions about the history of interrogation in this war than any single case alone could offer. The first conclusion is about the role and uses of interrogation. This was, after all, the war in which many different intelligence-gathering efforts thrived, yet where interrogation fits into this picture remains unclear.²⁵ The second conclusion is about the methods developed to get people to give information. Understanding the typical from the atypical experience in these camps – all of which were completely secret and, in theory, could have been lawless – shows what Britain considered acceptable behaviour amid total war. The camps in this book show that physical abuse was rare, but that psychological manipulation was an integral part of the process that emerged from the conflict. The book nevertheless does not overlook the fact that abusive interrogations did take place immediately after the war and outside Britain, especially in colonial counter-insurgencies, and the Epilogue reflects on this sharp contrast.

Important as the questions of how and why the state interrogated are, a comprehensive history of interrogation needs also to look at who was affected by it. The third conclusion concerns those who were caught up in these interrogation camps. We currently know only the tip of the iceberg – individual German spies who became double agents, such as Eddie Chapman; German generals who were held as prisoners of war, such as Ludwig Crüwell; and senior Nazis who were then tried as war criminals, such as Albert Kesselring and Nikolaus von Falkenhorst. A focus on these people, who were indeed interrogated in the camps in this book and who for various reasons stand out, nevertheless hides the fact that the overwhelming majority who passed through Britain’s interrogation camps were not Chapmans or Kesselrings, as neither were tens of millions of people who fought and suffered in this war. Most of the people interrogated were unremarkable in terms of their past and future trajectories. Yet much of the material that interrogation produced is about them. The temptation to simply focus on the individuals who stand out has been deliberately resisted. In keeping with the aim of allowing the material that interrogation produced to shape the analysis, the chapters use the stories of various individuals in order to bring to life the otherwise abstract categories of ‘soldiers’, ‘perpetrators and witnesses’, ‘agents and spies’. Through their interrogation reports, we see the different ways in which soldiers experienced the war, some of the dilemmas faced by civilians in occupied Europe and the messiness of investigating war crimes after six horrific war years – including cases that never reached a courtroom. We also see that many of the people interrogated did not conform to simple binaries of pro- or anti-Nazi, something that was realised at the time. All of this makes Interrogating Nazism as much a history of an intelligence process as of an intellectual one: that of Britain trying to comprehend the very enemy it was fighting.