The key part of the strategy was to attempt to hide the amount of troop buildup in Southern England, by developing threats across the European theatre, and to emphasise an Allied focus on major bombing campaigns.

Through the signals work at Bletchley Park, many of the German lines of communication were compromised since intercepts, codenamed Ultra, gave the Allies insights into how effectively their deceptions were operating.

Bodyguard was preceded in late 1943 by Operation Cockade, which was intended to confuse the German high command as to Allied intentions and to draw them into air battles across the Channel.

The departments responsible for deception, 'A' Force, COSSAC's Ops (B) and the London Controlling Section, began to address the problem of achieving tactical surprise for Overlord.

Codenamed Jael, a reference to the Old Testament heroine who killed an enemy commander by deception, it would have attempted to deceive the Germans into thinking that the Allies had delayed the invasion for a further year but instead concentrated on the Balkan theatre and on air bombardment of Germany throughout 1944.

The plan had a mixed reception in the Allied High command, and in October, a decision on the draft was deferred until after the Tehran Conference, a month later.

Instead, the core of the plan suggested misleading the Germans as to the exact time and location of the invasion and keeping them on the back foot once it had landed.

The new name had been chosen based on a comment by Winston Churchill to Joseph Stalin at the Tehran Conference: "In wartime, truth is so precious that she should always be attended by a bodyguard of lies".

It included Allied belief in air bombardment as an effective way of winning the war, with the 1944 focus on building bomber fleets.

Their cooperation was essential in creating the illusion of large-scale troop movements that would mislead the Germans and prevent them from reinforcing the Western Front.

However, persuading the Soviet leadership to participate and ensuring they fully understood the intricacies of the plan, posed a significant diplomatic challenge.

Col. John Bevan, the chief architect of the operation from the British side, and Col. William H. Baumer, his American counterpart on Eisenhower's staff, were chosen to present the plan and negotiate Soviet involvement.

The planners created Fortitude, building on elements of the earlier Cockade, which encapsulated an entire fictional Allied invasion plan against targets in France and Norway.

Its main undertaking was, through the various deception techniques, to overstate the size of the Allied forces in Britain through early 1944, enabling them to threaten multiple targets at once.

The Fourth Army had first been activated the previous year, as part of Cockade to threaten Norway and tie down the enemy divisions stationed there.

France was the crux of the Bodyguard plan: with Calais as the most logical choice for an invasion, the Allied high command had to mislead the German defences in a very small geographical area.

The Pas-de-Calais offered advantages over the chosen invasion site, such as the shortest crossing of the English Channel and the quickest route into Germany.

[18] General Bernard Montgomery, commanding the Allied landing forces, knew that the crucial aspect of any invasion was the ability to grow a beachhead into a full front.

[18] While Fortitude represented the major thrust of Bodyguard in support of the Normandy landings, several smaller plans added to the overall picture of confusion.

[19] The Twenty Committee, in charge of anti-espionage and deception operations of British military intelligence, feared the plausibility of the story and so did not promote it too heavily through their agents.

[22] That, combined with the fact that Bordeaux was an implausible target (the landing site was far outside the range of fighter cover from the United Kingdom), meant that the Germans took very little notice of the rumours and even went as far as to identify it as a probable deception.

[24] Despite not gaining much traction with the targeted governments, Graffham still influenced the thinking of German commanders and pushed them towards accepting other aspects of Bodyguard.

The operation involved meetings between several British and Swedish officials as well as the purchase of Norwegian securities and the use of the Double-Cross System to spread false rumours.

Sweden maintained a neutral stance during the war, and if its government believed in an imminent Allied invasion of Norway, that would filter through to German intelligence.

Building on the approach of Graffham, he hoped to support other Bodyguard deceptions in the Western and Mediterranean theatres by making political overtures to Sweden, Spain and Turkey.

'A' Force used similar tactics as before by simulating the existence of the Ninth, Tenth and Twelfth Armies in Egypt via exercises and radio traffic.

This information was transmitted at the behest of the British High Command in order to increase his credibility to the Germans and was done at a time when it was too late to fortify Normandy.

[44][45] The practice of using mock tanks and other military hardware had been developed during the North Africa campaign, especially in Operation Bertram for the attack at El Alamein.

For Bodyguard, the Allies put less reliance in those forms of deception since they believed that the German ability to directly reconnoitre England was limited.

Operation Bodyguard is regarded as a tactical success, delaying the Fifteenth Army in the Pas-de-Calais for seven weeks thus allowing the Allies to build a beachhead and ultimately win the Battle of Normandy.