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Codeword Overlord: Keeping D-Day top secret
Seventy-five years ago, on 6 June 1944, 168,000 Allied troops stormed ashore on the beaches of Normandy to begin the liberation of Nazi-occupied Europe, supported by 12,000 aircraft and nearly 7,000 ships. The invasion plan, initially codenamed Overlord and then designated Neptune and a dozen other subordinate components, was the largest amphibious assault ever contemplated, and was an extraordinarily high-risk enterprise.
The daunting requirement to deliver a large number of heavily armed soldiers, and their supporting weaponry, to a well-defended coastline imposed significant challenges. The key to success would be the element of surprise, but the enemy was fully aware that an invasion attempt was probable sometime during the summer of 1944. The only issues at stake were the precise timing, and the exact location. If the ultimate Allied objective was to cross the Rhine, occupy the industrial assets of the Ruhr and reach Berlin, the most direct route seemed obvious.
Conventional military doctrine dictated that the invading forces should be at sea for a minimum period, so as to avoid a major naval engagement in which the convoys of troopships would be bound to suffer heavy losses. The less time the troops were afloat, the smaller the chance of a U-boat attack, of convoys blundering into a minefield, or of discovery by an E-boat patrol, maritime picket or by aerial reconnaissance. These and similar considerations dictated that the most propitious route would be across the shortest distance, the 23 miles from the Kent ports to the Pas-de-Calais. As regards timing, the tides, moon and weather would be crucial.
Such a plan enjoyed many merits, including the opportunity to provide maximum air cover over the combat zone, with Allied aircraft requiring only the minimum time to return to base to refuel and rearm. Considering that a fully equipped Spitfire only carried enough ammunition to fire its .303 Browning machine guns for less than twenty seconds, this factor was likely to be mission-critical, especially as ground support and air superiority would be absolutely vital in seizing and holding any beachhead.
Another significant necessity was the logistical resupply, involving armour, food, fuel, ammunition and transport. Past experience of beach landings had demonstrated the need to capture a medium sized, deep-water port, with its handling facilities intact. This was a tall order, but the Calais region boasted several such towns, including Dunkirk and Boulogne, and opened up the possibility of cargo ships sailing directly from the United States.
Hitler understood the strategic implications of allowing a beachhead to be gained, and on 3 November 1943 he had issued Führer Directive 51 to prepare for what he saw as the coming Allied offensive. However, Field Marshal Rommel’s preferred solution was a swift armoured counter-attack mounted by some of the ten Panzer divisions already garrisoned in France.
The Allies’ masterplan was devilishly complex, involving the embarkation of troops at eleven different south coast ports, from Falmouth in the west to Newhaven in the east, destined for the five designated beaches in Normandy. In recognition of what might go awry, they deployed fifteen hospital ships, staffed by 10,000 doctors, and prepared 124,000 beds for potential casualties.
When weighed objectively, taking into account all the relevant military and political considerations, it seemed obvious that if the Allies were to have the slightest chance of overwhelming Rommel’s so-called impregnable Atlantic Wall, manned by fifty-eight divisions of the 7th and 15th Armies, they would have to assemble in south-east England and rush across the Channel to Calais during the full moon, at high tide, perhaps relying on a diversionary attack elsewhere to draw the defenders in the wrong direction.
Of course, we now know that the focus of D-Day was in Normandy, and that in the absence of any available ports the Allies constructed two huge Mulberry harbours off the beach where the pontoons were protected by sunken block-ships acting as breakwaters. Innovative engineers also designed and installed an underwater fuel pipeline code-named Pluto (‘pipeline under the ocean’), laid on the seafloor from Niton in the Isle of Wight, to sustain the invasion vehicles, thus reducing the need for vulnerable tankers to make the long voyage from Plymouth or Southampton in seas likely to be infested by an estimated 125 U-boats.
For many years much secrecy surrounded the concept of strategic deception, but a series of disclosures in the 1970s revealed that a group of ingenious American and British planners had persuaded the Allied Supreme Commander, General Dwight D. Eisenhower, that a gamble on Normandy in preference to the more obvious choice, might catch the enemy off guard and enable a sizeable beachhead to be achieved before encountering the danger of counter-attack. The argument was that the Oberkommando der Wehrmacht was predisposed to accept the Pas-de-Calais as the only sensible invasion objective, and the Allies possessed the means to reinforce this judgment by providing the necessary evidence. Indeed, the deception planners exercised control over the enemy’s network of spies, had access to his most confidential communications, enjoyed air superiority and could impose the very strictest security conditions on the British Isles that could not be matched anywhere on the Continent with its porous land frontiers. These factors combined to create a unique set of circumstances that could be exploited by an intelligence community that had experimented with deception schemes in the Mediterranean and Middle East to gain unprecedented experience of the art of misdirecting the Axis. The results achieved in those theatres suggested that skilful, co-ordinated manipulation of wireless traffic, double agents and camouflage could accomplish much by exaggerating strengths, disguising weaknesses and confusing the adversary.
The gamble, concealed by the codeword Bodyguard, was momentous in every respect. Experience gained at Dunkirk, Dieppe, North Africa, Sicily, Salerno, Anzio, Attu and Kwajalein showed that Allied troops were at their most susceptible when they made their way ashore in slow, poorly protected landing craft, to then negotiate the beach obstacles and evade the lethal crossfire from heavily fortified installations manned by seasoned veterans of the Russian front. The implications of a major defeat on the Cherbourg peninsula, with the invaders pushed back into the sea, would be dire, and certainly delay any further attempt for another year. Following his victory, Hitler would be free to move reinforcements to the east, and he would also have the benefit of the V-1 and V-2 onslaught on England. Perhaps, with his stock high, the Wehrmacht would not have been motivated to attempt a coup on 20 July, and he might have bought sufficient time, maybe an extra two years, to develop jet fighters and invest in an atomic bomb. This is sheer speculation, but such conjecture gives some context to what was riding on the chance to free Europe from Nazi tyranny.
Extracted from Codeword Overlord: Axis Espionage and the D-Day Landings by Nigel West
