I wish I was more knowledgeable about this, but the Dieppe raid was originally suggested under the cover of testing the feasibility of the Normandy landings. Though this was partially true, it was revealed last year that it was also a guise to try and capture an Enigma machine. This also opens up the secret can of worms that was Bletchley Park.

Source: http://globalnews.ca/news/274605/breaking-german-codes-real-reason-for-1942-dieppe-raid-historian/

If this is your kind of thing, William Breuer wrote an interesting, easy read about covert operations in WWII (you can say what you wish about the man as an author). In several instances it discusses the activities of Nazi (Abwehr and SD) spies in the United States that were eventually rounded up by the FBI. One was an executive in the motor industry, and posted an ad in an mechanical magazine asking for information about recent developments in the industry. He got dozens of useful responses about the technical specs of US military aircraft.

http://www.amazon.ca/Top-Secret-Tales-World-War/dp/0471078409