JOIN USThe piece of paper, which was a communication sent to the Nazis by their most trusted spy in Britain Juan Pujol Garcia, reveals how the agent gave deceptive information on Allies' D-Day landing plans in 1944.
Pujol, a Spanish businessman who was believed by the Germans as one of their top assets in the UK, was actually working for Britain's intelligence during the World War II.
The paper shows how the double-cross helped an elaborate British wartime plot succeeded in convincing Hitler that the Allies were about to stage the bulk of the D-Day landings in Pas de Calais rather than on the Normandy coast -- a diversion that proved crucial in guaranteeing the invasion's success in 1944, the BBC reported.
The key to the plot's success was however linked to the success of Bletchley Park -- the decryption centre depicted in the film 'Enigma' -- which had decoded the intercepted memo written with Enigma code.
This enabled them to monitor the success of their counter espionage and put in place the ultimate double cross that almost certainly shortened the war and save thousands of lives, said the report.
Over 10,000 people were employed at Bletchley Park and they were saluted by former British Prime Minister Winston Churchill who in his biography described them as "an army of unarmed intellectuals."
Now archivists at the site of the code-breaking centre hope that a new project to digitise and put online millions of documents, such as this document by Pujol, will uncover further glimpses into its extraordinary past.
According to the report, Pujol, who was referred as Garbo by British intelligence officials, used a fictitious web of informants and the reports he sent back to Germany were designed, ultimately, to mislead.
But the double agent was so completely trusted at the top level of the Nazi high command that he was honoured for his services to Germany, with the approval of Hitler himself, making him one of the few people to be given both the Iron Cross and the MBE for his WW-II exploits.
"He was no James Bond -- he was a balding, boring, unsmiling little man," Amyas Godfrey, an associate fellow at the Royal United Services Institute, was quoted as saying.
"But he had the Germans completely fooled. They thought the information he was sending was so accurate."
According to the report, Garbo gave some absolutely genuine information to the Germans to maintain his cover. But when it came to the looming Allied invasion of France, he fooled the Nazis.
Citing intelligence from his fake "agents", he informed the Nazis that the invasion had been a red herring and "critical attacks" would follow elsewhere -- most likely down the coast in Pas de Calais. He also falsely reported that 75 divisions had been massed in England before D-Day, meaning that many more were still to land in France.
It was an account the Nazis took extremely seriously and as a result, German troops were kept in the Calais area in case of an assault, preventing them from offering their fullest possible defence to Normandy.
When the document was decoded by experts at Bletchley Park, the Allies knew they could press forward with confidence that thousands of German troops would be tied up vainly standing guard at Calais.
The intercepted document has been found by volunteers digging through Bletchley Park's archives.