The plot cooked up by Ian Fleming in September 1940, more than a decade before he created James Bond, was so brilliantly preposterous that it can now be seen as the prototype 007 mission.

Fleming, in his role as a naval intelligence officer during the Second World War, was the architect of Operation Ruthless, a daring scheme to seize a German codebook that may have inspired the plot to From Russia with Love.

His plan, involving a staged plane crash and disguised commandos, is revealed in full at a new exhibition at the Imperial War Museum.

Operation Ruthless was composed after codebreakers at Bletchley Park realised that they could not efficiently decipher messages sent by the German navy without copies of their conversion tables. Fleming hatched a plan to “obtain the loot”.

His idea was to borrow a captured Luftwaffe bomber and fake a crash to attract one of the German rescue boats picking up downed air men in the English Channel. Fleming’s men would then overpower the crew and make off with their codebook.

“Pick a tough crew of five,”he wrote “including a pilot, W/T (wireless/telegraph) operator and word-perfect German speaker. Dress them in German Air Force uniform, add blood and bandages to suit.”

“Crash plane in the Channel after making S.O.S. to rescue service. Once aboard rescue boat, shoot German crew, dump overboard, bring rescue boat back to English port.”

The pilot, he noted with a novelist’s precision, should be a “tough bachelor, able to swim.”

Bletchley Park regarded it as a “very ingenious plot”. A Hienkel He 111 bomber and some German uniforms were sourced. Fleming put his team together and took them down to Dover to await a favourable moment.

It never came. The plan was eventually abandoned because of the lack of rescue boats operating at night. There were also concerns that the crew might be killed in the crash or drown before their “rescue.”

As Fleming himself put it after the Bond books became global bestsellers: “True Secret Service history is very fantastic... certainly no more or less fantastic than what happens in James Bond’s adventures.”

He was particularly good at dreaming up imaginative schemes. Among his odder ideas were: scuttling cement barges in the Danube to block the waterway to German shipping, forging Reichsmarks to disrupt the German economy, sinking a lump of concrete with men inside it off Dieppe to observe coastal defences and offering the French navy the Isle of Wight as French territory until the end of the war.

The exhibition For Your Eyes Only: Ian Fleming and James brings together many of Fleming’s personal effects with memorabilia from the books and films to discover where the identity of the debonair author ended and the fictional secret agent began.

They range from Fleming’s artery-clogging recipe for scrambled egg to the bikini worn by Halle Berry in Die Another Day.

According to James Taylor, the curator of the exhibition, Fleming only discovered a sense of purpose in 1939 after a dissolute career as a hard-living journalist and then “the world’s worst stockbroker”.

“The war was the first time that he found a role in life. The old school tie network got him a job as assistant to the Director of Naval Intelligence but he excelled in the role because of his own intellect, inventiveness and great personal charm.”

Rear Admiral Godfrey, Fleming’s boss and later the model for “M”, said that Fleming was “the only officer who had a finger in practically every pie.”

Fleming had a good war but fought it all from behind his desk in Whitehall.

Peter Smithers, a colleague in naval intelligence, said: “Ian constantly longed to be personally engaged in the excitement. He was of an essentially aggressive nature. It was the repression of all these desires by authority, quite rightly, which in my opinion fired the imagination engaged in his books.”

After the war Fleming became a journalist again and then a writer, dashing off Casino Royale in 1952 and 11 further Bond novels before his death in 1964, at the age of 56.

He was never again an espionage insider. Instead, as the exhibition shows, he reheated his wartime memories and transposed them to the Cold War.

Mr Taylor said: “Most of the heroes and villains in the novels grew out of his wartime experiences. But by the time he was writing, the real British secret service was in disarray with the defections of Burgess, MacLean and Philby the most embarassing examples.”

“Bond was a way of projecting Britain as a first rank power despite all this, to suggest that the plucky nation which won the Battle of Britain was still punching above its weight in the new world order.”

For Your Eyes Only: Ian Fleming and James Bond is at the Imperial War Museum from April 17 2008 to March 1 2009. Book tickets at www.iwm.org.uk/007 or on 020 7416 5439