But it really happened:
The answer is of course, Operation Cornflakes. Which is a lame name for a kickass project:
Operation Cornflakes was a World War II Office of Strategic Services PSYOP mission in 1944 and 1945 which involved tricking the German postal service Deutsche Reichspost into inadvertently delivering anti-Nazi propaganda to German citizens through mail.Pretty rad. Shame about the name. I guess they can't all be Operation Midnight Climax.
The operation involved special planes that were instructed to airdrop bags of false, but properly addressed mail in the vicinity of bombed mail trains. When recovering the mail during clean-up of the wreck, the postal service would hopefully confuse the false mail for the real thing and deliver it to the various addresses.
The content of the mail often included copies of Das Neue Deutschland, the Allies' German language propaganda news sheet. In addition, the postage stamps used were subtly designed to resemble the standard stamp with Adolf Hitler's face, but a close examination would reveal that his face is made to look like an exposed skull or similarly unflattering imagery. Also, the country identifier 'Deutsches Reich' (German Empire) read 'Futsches Reich' (Kaput Empire).
The first mission of Operation Cornflakes took place on 5 February 1945, when a mail train to Linz was bombed. Bags containing a total of about 3800 propaganda letters were then dropped at the site of the wreck, which were subsequently picked up and delivered to Germans by the postal service.
You can read more about Operation Cornflakes here.
Thanks to Slaky for tipping me off to the existence of Operation Cornflakes, and Dan for