Editing Operation Fortitude (section)

==Impact==
The Allies were able to judge how well Fortitude worked because of [[Ultra (cryptography)|Ultra]], the [[signals intelligence]] that was obtained by breaking German codes and ciphers. On 1 June, a decrypted transmission by [[Hiroshi Ōshima]], the Japanese ambassador, to his government recounted a recent conversation with Hitler and confirmed the effectiveness of Fortitude. When asked for Hitler's thoughts on the Allied battle plan, he had said, "I think that diversionary actions will take place in a number of places{{snd}} against Norway, Denmark, the southern part of western France, and the French Mediterranean coast".<ref name=HoltUltra>Holt 2004, pp. 565–566</ref> He added that he expected the Allies would then attack in force across the [[Strait of Dover]].<ref name=HoltUltra/>

The deception was also assisted by very high German assessments of Allied capabilities. In an appreciation of 8 May von Rundstedt said:{{sfn| Kenyon |2019|p=170}}

{{Quote|Observed tonnage of landing shipping could be taken as sufficient for 12 or 13 divisions (less heavy equipment and rear elements) for fairly short sea routes. In all (estimating the capacity of the other English ports not so far covered by visual and photo recce) probable employment of at least 20 and probably more divisions in first wave must be expected. To these must be added strong air-landing forces.}}

During the course of Fortitude, the almost-complete lack of German aerial reconnaissance, together with the absence of uncontrolled German agents in Britain, came to make physical deception almost irrelevant. The unreliability of "diplomatic leaks" resulted in their discontinuance. Most deception in the south was carried out by means of false wireless traffic and through German double agents. However, those methods had significantly less impact for Fortitude North. In his 2000 book, ''Fortitude: The D-Day Deception Campaign'', [[Roger Fleetwood-Hesketh]], a member of Ops (B), concluded that "no evidence has so far been found to show that wireless deception or visual misdirection made any contribution". It is thought that the Germans were not actually monitoring the radio traffic that was being simulated.<ref>Hesketh, p. 167</ref>

Overall, Fortitude was successful for several reasons:

* The long-term view taken by British Intelligence to cultivate double agents as channels of [[disinformation]] to the enemy.
* The use of Ultra decrypts of machine-encrypted messages between the [[Abwehr]] and the [[Oberkommando der Wehrmacht|German High Command]], which quickly indicated the effectiveness of deception tactics. That is one of the early uses of a [[Control theory#Closed-loop transfer function|closed-loop]] deception system. The messages were usually encrypted by [[Fish (cryptography)|Fish]], rather than [[Enigma machine|Enigma]] machines.
* [[Reginald Victor Jones]], the Assistant Director Intelligence (Science) at the British [[Air Ministry]], insisted that for reasons of tactical deception, for every radar station attacked within the real invasion area, two were to be attacked outside it.
* The extensive nature of the German intelligence machinery and the rivalry among the various elements.
* [[General (United States)|General]] [[George Patton]] was the leader whom the Germans feared the most, and they considered him the Allies' best general.<ref name=Beevor571/> Therefore, the German High Command believed that he would lead the daring attack.

One author says that on 5 June before he gave the ''Go'' message for Overlord, Eisenhower received a message that was couriered from Bletchley Park and had been sent by Hitler to Rommel with battle orders that the invasion of Normandy was imminent but that it was a feint to draw troops away from the real invasion five days later against the Channel Ports, and Rommel was not to move any troops. That would mean that the Allies would have five days without determined opposition. It was sent in a ''Fish'' radio message and decrypted by Colossus, according to an account by Tommy Flowers.{{sfn|Abrutat |2019|p=173}} Another author doubts whether Hitler would have sent messages about the invasion at the time since the invasion fleet had sailed on 4 June but was then postponed for 24 hours, and even with Colossus, Fish decrypts could take days or weeks. He thinks that Flowers may have embellished or misremembered the story in later life. Hitler’s views on the real invasion are widely attributed to the message from the Japanese ambassador to Berlin, Ōshima, after a 27 May meeting. Anyway, during the first week of June 1944, Eisenhower was more concerned with the weather than whether the Germans had been misled about the invasion's location.{{sfn|Kenyon |2019|pp=59,60,175}}