He’s torn. Ripped in opposite directions. Pulled this way and that, can Sefton Delmer even tell which is the real him?

At the age of ten, he is the only British boy in a German school in the opening months of World War I. It’s the first day of term. From the top of a hall packed with German schoolchildren he can hear the voice of the Herr Direktor—his headmaster—up above the crowd on the raised stage. The director’s voice is different today. He’s normally so calm, but now he’s shouting, screeching about the British, those wretched people who have brought this war upon peace-loving Germany and its peace-loving kaiser. The British, that nation of petty traders, are jealous of how Germany is rising, of Germany’s new wealth, of its expanding territories. The British have plotted long and deceitfully to encircle us, and now these British assassins have struck. It is a moment for death and glory.

When Sefton greets the other pupils in the changing room, the children who were his good friends just a few weeks ago, they all hiss back at him: “Verräter!” (traitor), and the words fill the room like the judgement of a lynch mob. After school, in the Tiergarten, the boys wheel around Sefton, surround him, and the fattest one sets upon him with his fists.

With every morning, assemblies grow more fervent. The boys march round and round the hall, dust rising from the floor as they stamp in circles, crying in unison, “God! Kaiser! Fatherland!” their lungs beating out songs about bloody dawns rising over vast armies, about the sweet yearning to perish on the battlefields just for the joy of seeing Germany’s banner flutter victorious.

He has to march with all the others amid the crash of cries, stamps, songs, chants. And although he knows it isn’t right to feel this way, he can’t help but be filled with enthusiasm, despite himself, by these hymns to German gunsmiths hammering the steel-hard German heart. And he finds his mouth prised open, finds the words take him over, and now he’s singing the German war songs even as they celebrate the destruction of his countrymen.

“To tell the truth,” Sefton Delmer would admit decades later, “I enjoyed singing the German victory songs. Their lift and lilt gave me a thrill of exultation of which I felt quite ashamed. ‘A British boy,’ I would say to myself, ‘has no business feeling like this about these German war songs.’”1

And who, in this moment, is the real Sefton Delmer? Which is his real voice, the one that expresses his “true” identity? The Sefton Delmer who sings along to German war songs? Or the one muttering resistance in English under his breath?

For Delmer, this strain, this splitting of the self, will go on to become the source of his strength and skill. He will grow up to become the nearly forgotten genius of propaganda, a man who understood the secret of how propaganda acts on people, famed for his ability to leave his own personality behind; to cross countries, battle lines and seemingly intractable divides; to reimagine himself as others, become the enemy, climb inside their minds—and then play tricks on them from the inside.

But this quality will also be his greatest vulnerability.

Germany. Summer 1941. Hitler and his allies rule Europe from the Atlantic to the Black Sea. In the West, Britain is isolated. In the East, Soviet cities are falling one after another. In Germany, the streets and squares of the Third Reich are covered in a forest of swastika flags, the red and black illuminated at night with the glow of torch-lit processions.

Triumphant Nazi propaganda celebrates Victory, Unity, Fatherland and Führer in posters and in the songs of schoolchildren, from loudspeakers and in the headlines of newspapers, on cinema screens, and—​most of all—from radios. Ever since they came to power, the Nazis have seen radio as the great force that can bind the country; break down the old divisions, the rifts among classes and regions; unite all Germans; and make real the grand claim of Propaganda Minister Joseph Goebbels that with the arrival of the Nazis, “the individual will be replaced by the Community of the People”: die Volksgemeinschaft, populated by Volksgenossen driving Volkswagen and reading the Völkischer Beobachter.2

The Führer’s speeches were special, festive celebrations, broadcast on radios and blared out from loudspeakers in streets, factories and offices. Every good German was expected to listen. At the sound of a wailing siren, you had to stop whatever you were doing. Whether at home or in an office, on the floor of a factory or in a barracks, life paused. When Hitler spoke, pistons and typewriters across the Reich fell silent. Wardens wearing swastika armbands patrolled the streets, ensuring that everyone was in hearing distance of a radio or loudspeaker so that the whole Volksgemeinschaft would, at one and the same time, be bathed in the Führer’s swelling sea of words about Germany. Germany, this community of fate, a people proud to obey a commanding will, resurrected after years of poverty and misery brought on by cold-blooded foreign powers who, despite our hand of friendship, have forced war on Germany, a war begun by the British and by the Jewish newspapers, by Jewish finance and Jewish Bolsheviks, by parasites, by enemies against whom, I prophesy, we will be victorious. We shall fulfill our destiny. We are the salvation of Europe. Sieg Heil!

Radio helped the Nazis. But it also helped people escape from them. Twiddle the dial on one of the more elaborate radios, and you could slip into other worlds on shortwave. Even cheaper medium-wave radios could, with the help of a few choice wires acting as improvised antennas, be used to travel beyond the official stations of the Reich.

The Nazis knew this vulnerability. Tuning in to foreign broadcasts, and especially to the hated BBC, was a crime punishable by hanging. Foreign radios were jammed. Hitler’s and Goebbels’s speeches repeatedly told about the perfidious lies of enemy propaganda, especially from the British.

Listening to foreign radio stations was something to try only with your most trusted confidants—you never knew who might be listening in. The SD, the Sicherheitsdienst (intelligence agency) of the SS, was created to keep every person in the Reich under “continuous supervision”. Every week these SD reports, delivered by their myriad agents, were collated into an overall analysis of the “attitudes and behaviours of the Volk”, and their radio-listening habits were of special interest.3

In July 1941 the SD tersely noted that Germans (especially those in Chemnitz, Hamburg, Berlin and Potsdam) were tuning in to a new clandestine shortwave station called Gustav Siegfried Eins.4 This secret station was more insidious than the foreign broadcasts. You could legislate and smear foreigners—but here was a seditious voice coming from inside.

Gustav Siegfried Eins opened with the same tune as the main Nazi news show—but instead of the great bells of Weimar, it was played on a wonky-sounding piano. Then an adjutant came on air and announced that der Chef was about to speak.

There was something almost dagger-like in der Chef’s tone: sharp, maybe drunk, definitely bitter. He swore incessantly, with racial slurs about Yankee-swine, stink-Japs, Russian pig–Bolsheviks and Italian lemon-faces. He called Churchill a “dirty, Jew-loving drunk”.

Der Chef loved the army but loathed the Nazi Party. Instead of a Volksgemeinschaft, he attacked what he called “die Parteikommune”, as if the Nazi Party was a clique unto itself. He blamed party officials for living the high life during holidays on the Dalmatian coast while people at home were being bombed by the Royal Air Force. He respected Hitler, who was the sort of man he had fought next to in World War I, but he accused Himmler, Göring and the rest of being soft on Britain. Hadn’t they seen the destruction the British caused in Cologne and Aachen after they launched their first bombing raids in May? When the damn air-raid sirens in Aachen didn’t work and whole swathes of this great German cathedral city were destroyed? Der Chef had been to Aachen, had seen the weeping German women clambering over the wreckage of their houses trying to dig out their children underneath—and what had the Luftwaffe done in response? Nothing. London should be bombed to smithereens. Those shit Britishers should be blown to shit. But the Luftwaffe was docile. The Nazi Party was full of secret Bolsheviks. They didn’t even tell soldiers when their relatives were killed in British bombings. They promoted their SS pals to easy office jobs. They frequented their exclusive SS brothels while soldiers died of dysentery on the front.

Every day, at ten to the hour every hour, for ten full-throated minutes, der Chef flew through this fury. He mentioned names of specific Nazi...