Helen Fry argues for the importance of a little-known British intelligence program both for the outcome of World War II and for current historians of the war and Nazi Germany. From 1939 until 1945, British intelligence agents covertly listened in on their German prisoners’ private conversations, which yielded “a wealth of information” (274) on German weapons technology and operations. Fry's primary sources of evidence are the transcripts produced by British military intelligence “listeners” who bugged the private quarters of thousands of German prisoners of war. These transcripts appear comparable to similar recordings produced by Americans eavesdropping on their own German prisoners during the same period, both of which were declassified in the late 1990s to early 2000s. These sources, and the methodological problems they present (numerous German memoirists argued that the prisoners were well aware that their quarters were bugged, and so perhaps their statements were not quite as unguarded as Fry describes) have been explored by Norman J.W. Goda and David Bankier (Secret Intelligence and the Holocaust [2006]) and Derek R. Mallett (Hitler's Generals in America: Nazi POWs and Allied Military Intelligence [2013]), although not to the extent that Fry does here.

The Walls Have Ears contains three main points of emphasis, two of which are executed more successfully than the third.

First and foremost, this is a book about what Fry characterizes as “a brilliantly conceived and spectacularly successful strategy to extract information from German prisoners of war” (2). Fry describes the British interrogation program and the backgrounds of the “listeners” in remarkable detail. Given the scale of the program, which expanded from a few rooms in the Tower of London in 1939 to additional sites at Trent Park, Latimer House, and Wilton Park by the end of the war, British intelligence turned to both women and German émigrés (many of whom were Jews) to fill the ranks of the dedicated linguists and transcribers tasked with differentiating otherwise anonymous voices from one another. Here the reader is treated to interesting and often amusing observations about the mechanics of the British deception program that exploited the self-regard of its higher-ranking prisoners. Upon arrival at the interrogation centers, German officers were subjected to sham interrogations, meant to convince them that their British captors were incompetent while also priming the prisoners to talk among themselves afterward. Housed in luxurious private rooms in compounds such as Trent Park and permitted to move freely about the grounds, these prisoners were also routinely buttered up with sojourns to London and surveilled by German refugee “stool pigeons” posing as prisoners, planted among them to encourage open conversations outside of the interrogation rooms. Meanwhile, seemingly every conceivable object from the lamps to the trees in the gardens was bugged, ceaselessly transmitting a stream of information to the British minders (105).

Secondly, through her careful attention to the documentary record of daily life in the interrogation centers, Fry suggests that an untapped resource exists in the archives, consisting of tens of thousands of pages of conversations that provide additional insight into German soldiers and officers’ attitudes toward the war, their political beliefs and views of the Nazi Party leadership (98). The prisoners’ near-constant carping and gossiping, and in-fighting between Nazi true believers and their more politically disillusioned comrades, provides revealing discussions of politics, war, and genocide. Routine complaints about Hitler and his minions articulated by the prisoners and captured on tape informed Allied propaganda against Germany. Other conversations highlight the insidiousness of Nazi antisemitism. Several prisoners slated for transfer to the United States in 1943 worried that they would be given over to the Jews and paraded through the streets of New York (129). Other prisoners, particularly in 1942–1943, spoke openly among themselves about their knowledge of or complicity in the unfolding Holocaust or other war crimes. Such reminiscences occasionally provoked laughter from the other prisoners (226). Although the listeners carefully catalogued and preserved every recording that dealt with atrocities, the files were never released to prosecutors after 1945, largely because of concerns that their public unveiling would jeopardize ongoing postwar eavesdropping operations (254–58).

Ironically, it is in the sections dealing directly with the information gleaned from the German prisoners and contextualizing its importance for the war effort that The Walls Have Ears is less conclusive. On the one hand, Fry can ascertain instances of direct cause and effect, where discrete data obtained covertly through eavesdropping was used to further the Allied war effort. For instance, in 1940, idle German chatter about the technical workings of radio-based Luftwaffe guidance and navigation systems and the locations of German transmitters allowed the RAF to target those sites (46–48). Likewise, in 1944 British intelligence used prisoners’ conversations to uncover the locations of U-boat bases in France unobtainable from RAF reconnaissance flights (176–78). However, Fry's discussion of other matters, such as the V-1 and V-2 weapons programs, are overly broad, given the often vague excerpts presented in the text of German prisoners avidly discussing the deployment of “wonder weapons,” the rumors of which ran rampant in German society during the war and belied little actual knowledge of the weapons’ existence (apart from such specific revelations that a Dr. Von Braun was working on them at a secret site at Peenemünde).

Indeed, as Fry acknowledges throughout the text, the project of intelligence gathering was highly collaborative, with the listening program steering the prisoners to discuss certain subjects based on intelligence from field agents in other agencies, sometimes provided by Allied partners. It is thus exceedingly difficult to try to apportion credit for wartime successes to one discrete office or operation, as Fry attempts to do here. Nevertheless, Fry's conclusion that there is much more good work for historians to do in these files is certainly warranted (273–74).