Tapping the Hot Line

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Geheimschreiber

Back on September 7, 1941, Leningrad had been under direct German fire for three days. The famous siege of nine hundred days was about to commence. Immediately to the east, at a place called Shlisselburg, troops of the Soviet NKVD desperately resisted advance elements of the German Sixteenth Army. Three hundred aircraft of the German Luftwaffe swept in to strafe the holdouts, and by nightfall the city on the shores of Lake Ladoga was engulfed in flames.

Far to the south, but also on the eastern front, panzer chieftain Heinz Guderian had turned his tank columns in a drive across the Russian rear in the Ukraine. He soon would meet another German pincer sweep and close the vast encirclement of Kiev. At the center of the eastern front another huge haul of prisoners and territory was in prospect for the German Army Group Center driving toward Vyazma.

A world in such tumult paid little attention to a radio-telephone call late that day from still-peaceable Washington, D.C., to London. In that innocuous pulsing across the Atlantic—also the scene of raging war—a newly arrived British official merely asked his superiors in London to provide him an assistant.

Innocuous as the call may have seemed, the German enemy heard, recorded and understood the conversation—no matter that it was “scrambled.” The occasion, in fact, was a red-letter day for a certain set of German eavesdroppers—this was their first intercept of many on the very same transatlantic “line” that Winston Churchill and Franklin Roosevelt would be using throughout the war to discuss Allied strategy, tactics, and policy.

If the Allies had their super-secret ULTRA code-breaking operation as an ear to Nazi Germany’s pulse, the Germans, as an intelligence coup of their own, had solved the Allied “scramble” device and could listen in when the two heads of state, or their many functionaries, picked up the scramble phone on either side of the Atlantic.

So secret was ULTRA that only the highest Allied officials and the most select intelligence personnel knew about it. So secret, likewise, was the German radio-telephone intercept that military intelligence was left out of the game almost entirely. Hitler and his closest Nazi Party coterie kept this one pretty much to themselves.

And they could thank the man equivalent to America’s postmaster general for the coup, rather than Germany’s professional spies.

Ladislas Farago told the story of Reich’s Post Minister Wilhelm Ohnesorge’s contribution to the German war effort in the 1971 book, The Game of the Foxes. The tale actually begins in 1939, when a German agent in New York noticed a story in the New York Times that was headlined: “Roosevelt Protected in Talks to Envoys by Radio ‘Scrambling’ to Foil Spies Abroad.”

Roosevelt’s scrambler was located in a soundproof room in the basement of the White House. Later in the war, Churchill would do his conversing from a scramble instrument located in his underground War Cabinet Rooms in London. For the moment, though, America was still a neutral party, and FDR’s first use of the scramble phone had been to hear about the unprovoked German invasion of Poland on September 1 from his ambassador in Paris, William C. Bullitt.

Developed by Bell Telephone, the A-3 scramble device would break up the frequency band and scatter the voice impulses at one end, all to be sorted out by a descrambler at the other end of the radio-telephone link. From the White House, FDR’s conversation was piped into an AT&T security room in New York for the transatlantic transmission in unintelligible form.

The German spy in New York dutifully forwarded his clipping from the Times, but in Germany there was no immediate or significant reaction within the intelligence community. Still, the Allied “hot line” did interest one expert outside normal German intelligence circles—Wilhelm Ohnesorge.

As Reichs post minister, Ohnesorge was in charge not only of Germany’s postal system, but also its telephone and telegraph network. He was just the man to focus upon the ballyhooed radio-telephone “scramble” link between England and America, which he did without delay. His laboratories and engineers set to work entirely lacking in visible evidence of the highly secret Bell apparatus—no blueprints, models, or the like. But, beginning his work in 1940, Ohnesorge’s chief research engineer, Kurt Vetterlein, had developed experimental models of both the scrambling and descrambling devices by September 1941. The first interception was of the British official’s call to London from Washington late on September 7, even as Leningrad came under siege.

Keeping their experimental work secret, Ohnesorge and Vetterlein soon perfected their intercept system. They built a monitoring station on the coast of occupied Holland, complete with directional antennas to pick up the radio signals from nearby England. By March 1942, they were ready to begin their intercepts on a regular basis.

At this early stage of the war—for America, especially—FDR and Churchill had a great many military secrets to talk about. The Normandy invasion was still two years away; the Anglo-American invasion of North Africa was still months in the future, and for both Allies, the war in the Pacific against Germany’s Axis partner Japan still appeared an unmitigated disaster.

As David Kahn further explained in his 1978 book, Hitler’s Spies, wartime developments gradually encroached upon the listening unit’s original location in a onetime youth hostel on the Dutch coast. Commando raids on coastal radar stations prompted the Germans to move their Forschungsstelle, or “research post,” to Valkenswaard in southeastern Holland. “Here a compact brick-and-concrete bunker, in the shape of an L, was built for it in the woods….” wrote Kahn. “The men worked in areas guarded by inch-thick steel doors, cooked in their own kitchen, slept in rooms with dormer windows, and relaxed in a living room with a fireplace.”

By the fall of 1944, after the Normandy invasion, the exigencies of war forced the Germans to relocate again—this time as distantly from England as Bavaria. “But here the distance from the [England-based] transmitter considerably impaired its results.”

The original, early war locale, of course, had been the best for Engineer Vetterlein’s operation. That spot, two hundred yards from the sea, “could pick up both the ground wave of the transmitter in England and the back lob of its beam toward America.” Vetterlein’s equipment included single sideband receivers, filters, modulators, switching equipment, tape recorders, timers and, for the intercepts themselves, two rhombic antennas. The latter took in the Allied signals in their scrambled form, but with the supporting equipment, Vetterlein and his men would find the Allied chitchat “instantaneously disentangled by the apparatus, and tape-recorded in the clear.”

As Kahn also noted, Vetterlein did not exactly begin his work from a point zero. His Deutsche Reichspost agency had owned an A-3 device allowing radiotelephone communication with the United States. The trick for Vetterlein and his crowd was to descramble, even if they understood the operating principles.

Thus, they first attacked the problem using American transmissions intercepted near occupied Bordeaux, France. They “attacked the problem with oscilloscopes and spectrographs, filters and patience. By the end of 1940, they had reconstructed the A-3’s secret parameters—the widths of the subbands, their division points, their inversions, and their intersubstitutions, which changed thirty-six times every twelve minutes.”

The painstaking work led eventually to the equipment that would descramble the overheard conversations “as they were being spoken,” although it did take months—until fall of 1941—to effectively intercept and descramble the cross-Atlantic messages. Later, when the intelligence operation was in full swing, the Germans monitored the hot line around the clock, with thirty to sixty calls to choose from every day.

Churchill and his counterpart in Washington would not discuss everything by radio-telephone, to be sure. They did have their wartime conferences; they communicated by other means, and they had many subordinates shuttling back and forth. Many of those subordinates, however, both military and diplomatic, would be using the scramble phone too.

Unknown to any of the Allied principals, the German monitoring station first located in Holland produced an intelligence bonanza from the start. “Its equipment was so efficient,” wrote Farago in his book, “that the intercepted conversations could be ‘deciphered’ instantaneously, losing only a few syllables after each key change (which occurred at intervals of twenty seconds) until the proper key was found automatically. The German transcripts were sent to Berlin on a G-Schreiber, a classified teletype that had its own scrambler system. The entire operation, from the interception to the arrival of its transcript in Berlin, usually required only a couple of hours. It was probably the fastest means of intelligence procurement in secret service history.”

Reichs Post Minister Ohnesorge waited until the intercept system was working perfectly before informing Hitler of the great success. On March 6, 1942, he wrote the Führer to report that his was the only agency in the Third Reich “that succeeded in rendering conversations that had been made unintelligible, intelligible again at the instant of reception.”

As a direct result, among other helpful intelligence gleanings, the Germans in July of 1943 were able to confirm that the Italian government, having deposed Mussolini, was seeking an armistice with the Allies.

Various signs had pointed toward the wavering of the Italian ally, but Hitler and his close advisors were unsure what to expect. When Marshal Pietro Badoglio’s new government took over on July 25, confusion reigned in Nazi Germany’s highest councils.

On July 29, however, Post Minister Ohnesorge’s latest intercept, delivered in a sealed envelope marked with a big U, settled the controversy—and resulted in Hitler’s next fateful decision. At 1 A.M. that day, Churchill and Roosevelt had talked on their scramble phone about the tumultuous events in Italy. They had discussed the possibility of an impending armistice with the new government.

Since there had been no official peace-feeler by the Badoglio regime, they might have been premature in anticipating such a move just then. And they apparently did speak in a conditional sense, even if their expectations were made quite clear.

Whatever the tone of the conversation, it was enough for the eavesdropping Germans. They saw it as hard evidence that armistice negotiations were under way.

As a result, Hitler’s uncertainty was ended. He immediately ordered the occupation of Italy, and soon twenty German divisions stood in the Allied pathway up the Italian boot, instead of the mere eight that were stationed there before the telephone intercept. The Allies would spend the rest of the war subduing the German forces in Italy—at horrendous cost to both sides.

While the Deutsche Reichpost had more than proved the value of its listening post in Holland, Germany’s military forces were not often to share in the intelligence harvest that resulted. “This was a Nazi triumph, and it was to remain a Nazi operation,” wrote Farago. “Distribution of the intercepts was strictly limited. A single copy of the original transcript was sent to Heinrich Himmler to be distributed at his discretion. The [military] Abwehr was bypassed, as were the intelligence departments of the Army, Navy, and Luftwaffe.”

After SS Chief Himmler’s scrutiny of the incoming intercepts, the “choicest” were sent on to Hitler. A few went to Foreign Minister Joachim von Ribbentrop, but he apparently was discouraged by the fact that the Allied speakers on the radio-telephone were often guarded even in their scrambled conversations. “Owing to the fact that these conversations are camouflaged,” he once complained, “there is very little one can learn from them.”

Wiser members of the Third Reich’s ruling circles were, of course, more impressed. The Himmler protégé Walter Schellenberg, who had vaulted to head of all German espionage by 1944, recognized an obvious “bull’s-eye” when the Holland intercept picked up an FDR-Churchill conversation on May 5, 1944, about an Allied buildup in England. There, straight from “the horse’s mouth,” was confirmation that the invasion of France was imminent. And when it did take place, just a month later, it wasn’t the Deutsche Reichspost’s fault that Germany was unable to stop it. Germany’s postmaster general and his engineers had done their job—what could be done about the information they provided was another matter altogether.

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