Bruce Schneier recently wrote a bit about the Aspidistra transmitter which the Allies used during World War II to spread disinformation in Nazi Germany.
During air raids, the Germans would turn off their radio transmitters so the Allies wouldn’t be able to use them for direction finding. As soon as the genuine German transmitters went off the air, the Allied deception would kick in. According to Wikipedia,
When a targeted transmitter switched off, Aspidistra began transmitting on their original frequency, initially retransmitting the German network broadcast as received from a still-active station. As a deception, false content and pro-Allied propaganda would be inserted into the broadcast. The first such “intrusion” was carried out on March 25, 1945, as shown in the operations order at the right.
On March 30, 1945, “Aspidistra” intruded into the Berlin and Hamburg frequencies warning that the Allies were trying to spread confusion by sending false telephone messages from occupied towns to unoccupied towns. On April 8, 1945, “Aspidistra” intruded into the Hamburg and Leipzig channels to warn of forged banknotes in circulation. On April 9, 1945, there were announcements encouraging people to evacuate to seven bomb-free zones in central and southern Germany. All these announcements were false.
The German radio network tried announcing “The enemy is broadcasting counterfeit instructions on our frequencies. Do not be misled by them. Here is an official announcement of the Reich authority.” The Aspidistra station made similar announcements, to cause confusion and make the official messages ineffective.
You have to love the sheer stupidity of the Nazis telling the German people the airwaves have been compromised by the enemy, but adding you can trust this broadcast. Maybe Hogan’s Heroes wasn’t all farce after all.