British intelligence chiefs tried to guess Hitler's plans by studying his horoscope, according to files released by the National Archives.
Hungarian Ludwig von Wohl persuaded senior intelligence figures that he could replicate the forecasts of the Nazi leader's personal astrologer.
He claimed that if London knew what advice Hitler, born on 20 April, was getting, they would know his next move.
But the security service MI5 had warned that von Wohl was a "charlatan".
Von Wohl, who was also known as Louis de Wohl, was a controversial figure.
Although he was dismissed as a buffoon and a scoundrel by some of the military people he met, others suggested that he was extremely astute, with a keen insight into the thinking of leading Nazis.
Despite dismissing his claims of being from Hungarian nobility, MI5 hoped de Wohl could feed them information about his clients among the "great and the good".
But the Special Operations Executive (SOE) - the wartime sabotage organisation - recruited de Wohl for its SO2 propaganda section, giving him the rank of captain and an army uniform.
He is said to have loved to "strut" around London in his military clothes.
In 1940 SOE sent de Wohl on a lecture tour of the United States aimed at convincing a sceptical public that Hitler could be defeated, and therefore that the US should enter the war.
His mission was regarded as a great success, with his talks and interviews being given significant publicity.
But the Japanese attack on Pearl Harbour in December 1941 dramatically brought the US into the conflict as Britain's ally.
De Wohl returned to London and then came up with his proposal to examine the astrological advice being given to Hitler by Swiss stargazer Karl Ernst Krafft.
De Wohl claimed that as Hitler relied heavily on Krafft's predictions, which were based on mathematics surrounding birthdates, the British could gain a unique insight into his thinking if they knew the astrological advice he was receiving.
The plan appealed to some leading figures, including the Director of Naval Intelligence Admiral John Godfrey, who found Hitler's erratic strategic moves hard to work out.
While his plan was enthusiastically embraced by member of SOE and the Political Warfare Executive, MI5 and MI6 were appalled.
"One of our senior officers comments that he cannot believe that anyone is going to re-employ this dangerous charlatan and confidence-trick merchant," a report from MI6 said.
Another MI5 officer said none of de Wohl's predictions had come true, apart from his forecast of Italy's entry into the war, which he made when it was "quite patent to anybody with the slightest knowledge of international affairs".
Historians now say that Hitler took no notice at all of astrological forecasts.
All the released files can be viewed at the National Archives in Kew, west London.