He proposed to take a captured German plane, fill it with German-speaking Brits, crash it into the English Channel, wait for a German rescue boat to come by, board it, sabotage it, and run off with the loot. (Or, in Fleming's brilliantly terse formulation: "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.") Even better, he was able to put together a team and await the opportunity to put his plan into action -- but one never came up, and higher-ups started to worry about the crew being killed in the crash or drowning.
The Times speculates that this may have inspired the plot of From Russia With Love, which involved a mission to steal a Russian encryption device. But I'm not sure even Bond would have been up for the mission on which Fleming was about to lead a few real-life British sailors. Hats off to the guy. His fictional creation doesn't have much on him. You can find tales of Fleming's other WWII exploits on his Wikipedia page, but this one seems to be new.
[hat tip: Movie City News]