'Cornflakes' was a US psychological warfare undertaking by the Office of Strategic Services to trick the German postal service into delivering Allied propaganda to German addresses (1944/45).

The operation involved the use of aircraft to drop bags of properly addressed mail in the vicinity of the mail cars of trains which had been attacked from the air. On recovering the mail, the postal service would, it was hoped, mistake 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 new sheet. In addition, the 'postage stamps' affixed to the false main were carefully designed to resemble the standard stamp but with Adolf Hitler’s face made to look like an exposed skull or another equally unflattering image.

The OSS’s Morale Operations Branch searched constantly for new ways to deliver propaganda, and one method was adapted from a Hungarian operation and supervised by Morale Operation’s John Fistere. This 'Cornflakes' was developed by Jan Libich and Jack Daniels late in 1944 and involved 21 Morale Operations personnel. After Libich investigated the workings of the German postal system, replicas of mailbags were made, complete with official markings. The bags were then filled with propaganda items such as poison-pen letters, 'black' newspapers, leaflets and posters bearing forged and cancelled postage stamps as well as actual addresses gleaned from pre-war German telephone directories. Aircraft of Major General Nathan F. Twining’s US 15^th AAF and Colonel Daniel S. Campbell’s US 14^th Fighter Group then dropped the bags during the course of routine bombing and strafing missions of railway marshalling yards and trains in Germany between February and April 1945.

Care was taken to ensure that the targeted areas were on the actual routes where the mail was addressed, and postage stamps were cancelled to coincide with the date of the raids. The planners reasoned that Germans finding the bags would assume they were from destroyed mail cars and return them to postal authorities, by whom the contents would be distributed with the 15 million other pieces of mail handled daily, thereby solving what would otherwise have been a major distribution problem.

The operation was described as a major success, and it was claimed that 'Cornflakes' weakened civilian and military morale, added more confusion to an already chaotic communication and transportation network, and convinced many Germans of the existence of significant anti-Nazi groups within Germany.

Some 20 such missions were conducted, and these delivered 320 bags of propaganda materials. Post-war interrogations of German prisoners revealed that many soldiers received copies of Das Neue Deutschland via 'Cornflakes' mail, resulting in many Gestapo investigations and prosecutions.

Though air dissemination was the key to the Morale Operation’s distribution requirement, US air commanders were not always co-operative. Late in the war, Morale Operations decided to drop millions of issues of Das Neue Deutschland from heavy bombers to supplement the normal 75,000 copies distributed through agents. The Psychological Warfare Branch of the Allied Forces Headquarters immediately protested that if Morale Operation’s 'black' material was found in the proximity as the Psychological Warfare Branch’s 'white' propaganda, it would have a deteriorating effect on both. Morale Operation’s solution, revealed in 'Pig Iron', was to reduce the size of the newspaper and label each with the message that it was a reprinted issue of the original product captured by Allied troops. This version, measuring 10 by 6.5 in (254 by 165 mm), was at first dropped over Germany at the rate of 1 million copies per month but later of 1 million copies per week. More than 10 million such small newspapers were eventually disseminated.

Forgeries were always a staple of the 'black' propaganda generated by the Office of Strategic Services. Morale Operations developed postage stamps bearing the likeness of Reichsführer-SS Heinrich Himmler rather than Adolf Hitler to give Germans the impression that the latter had been ousted in a secret coup. In conjunction with the British Political Warfare Executive, Morale Operations produced counterfeit ration cards and forged civil certificates, forms, vouchers, military travel orders, and sick leave and furlough passes. The Office of Strategic Services' Planning Group even considered counterfeiting German currency to destabilise the German economy. In another plan, to increase the likelihood of troops picking up Morale Operation’s material, it was suggested that propaganda be printed on the back of counterfeit banknotes or that special offers of rations or privileges be guaranteed to a person bearing the note when surrendering.

In co-operation with the Office of Strategic Services' research and development branch and the UK’s Political Warfare Executive, Morale Operations also developed a variety of unusual gadgets intended to lower morale, such as an exploding ink pen. Another idea was to produce ammunition in German calibres but filled with HE rather than smokeless propellant. Smuggled into the German military supply system, the rounds would, on being fired, explode to destroy the weapon and kill the firer.