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  • Normandy Crucible by John Prados

    The Decisive Battle that Shaped World War Two in Europe

    The Allied Intelligence Advantage

    Cobra's breakout took American troops through a succession of ruined villages and towns. Here a Stuart tank and other armor passes a road control team on its way to find the Germans, July 27. (c. National Archives, Normandy Crucible, Amberley Publishing)

    The first-generation histories of D-Day and the Allied campaign in, and breakout from Normandy were written at a time when the success of Allied codebreakers remained a deep secret. Hence the contributions of ULTRA, an umbrella term for the product of work against the German codes, was lost to history. Since the 1970s and the revelation of ULTRA, conversely, this intelligence source has often been represented as omniscient, making the Allies supremely aware of every Nazi maneuver. Neither version is correct. There were inherent limitations on what potential ULTRA had, but given those boundaries, it is impressive what advantages the codebreakers provided for the Allied side in this decisive campaign in the West.

    For the European Theater, codebreaking activities were centered at Bletchley Park, location of the British Government Code & Cypher School (GC&CS). By the spring of 1944 some 5,600 people here worked on deciphering, translating, or interpreting messages intercepted by legions of radio operators located throughout the war zones. British and Americans worked together. But what they could accomplish also depended upon what was possible. We have actual data on German communications for just one day—January 31, 1945—because Hitler’s operations staff chief, Colonel General Alfred Jodl chose to record the numbers. That day Fuehrer Headquarters fielded 120,000 telephone calls, sent or received 33,000 messages by high-speed teleprinter (geheimschreiber), and dealt with 1,200 radio messages. Only the radio messages—if intercepted—were fully vulnerable to decryption. Teleprinter traffic was proof so long as it went by landline (sometimes radio transmission became necessary). Between July and September 1944, for example, the Allies recovered an average of only 56 of the teleprinter messages daily, a minute fraction.

    The other key drawback was that ULTRA could provide only what passed over communications. For example, Hitler gathered the German commanders Von Rundstedt and Rommel at Margival on June 17 where they made a strategic decision to respond to the Allied invasion by means of a multi-corps offensive. Many German actions over subsequent weeks concerned gathering the forces for such an attack, finding a target, or countering Allied moves which could make the offensive impossible. But the only message traffic about Margival concerned Hitler’s movements or those of his generals.

    Vital to assisint the Normandy breakout, the French Resistance helped in all manner of ways. Here a Jedburgh team receives its final briefing in London before parachuting into France. (c. National Archives, Normandy Crucible, Amberley Publishing)

    Given those caveats, a survey of ULTRA revelations during the Normandy campaign shows just how valuable it was:

    – ULTRA plus radio direction finding identified the headquarters of the Germans’ Panzer Group West, hit by a powerful air raid on June 10, wounding its commander, Colonel General Geyr von Schweppenberg.

    – Hitler suspected his generals of defying orders to send more troops into the Norman port of Cherbourg, demanding a run down on the garrison. ULTRA got the June 18 response, providing Allied leaders with a complete order of battle on the Germans at Cherbourg.

    – On June 24 ULTRA could report that the II SS Panzer Corps, with 9th and 10th SS Panzer Divisions, were arriving at the front, but that they had had to detrain in eastern France, almost a week earlier. This bespoke the effectiveness of the French Resistance and Allied air attacks in disrupting German communications.

    – On July 5 ULTRA warned that the powerful Panzer Lehr Division would transfer from the British to the American sector. This came in time for air attacks to block roads, delaying the move. A few days later ULTRA warned Panzer Lehr would attack.

    – To help General Montgomery’s operations, on July 10 and 14 ULTRA provided the troop list for German forces defending the Bourguébus sector.

    A platoon of 2nd Armored Division tanks waits outside a village on August 10 for orders to resume the advance. (c. National Archives, Normandy Crucible, Amberley Publishing)

    – When the Americans moved to break out of their end of Normandy by means of Operation Cobra, ULTRA provided a succession of intelligence tips—quickly, that German stocks of artillery shells were running short; on July 26 a complete order of battle for the defending German LXXXIV Corps; on the 28th and again two days later that the corps had lost contact with its entire left wing; on July 29 warning of a panzer concentration for an attack into the U.S. flank; and on July 30 notice that the battered Panzer Lehr Division had begun leaving the front.

    – During the first week of August ULTRA reported the concentration for what became the Germans’ Mortain offensive, and, when that appeared to fail, on August 9 a Fuehrer order to continue the attack, even though risking being caught in the developing Falaise Pocket. Ironically, Hitler sent his order by radio because, after the July 20 Plot, he did not trust the landline networks to transmit his directives.

    – On August 17 ULTRA intercepted six of the ten parts of the message from the German high command in the West to withdraw from Normandy, beginning the Nazi maneuver to escape the Falaise trap. That the Allies ultimately could not seal the Nazis in was a product of tense command decisions, German desperation, and field coordination problems, not a lack of intelligence.

    Lyman B. Kirkpatrick, an intelligence officer with Omar Bradley’s American army group, once wrote that 70 percent of the best came from combat intelligence, by which he meant aerial scouts, the Resistance, and prisoner interrogation. This list of ULTRA accomplishments shows that Kirkpatrick indulged in a bit of deception of historians. Alternatively, the 30 percent includes some pretty incredible intelligence, which went far towards ensuring Allied victory in Normandy.

    John Prados's new book Normandy Crucible: The Decisive Battle that Shaped World War Two in Europe is available for purchase now.

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