Wireless intercept deception played a critical role in most military operations. In doing so, combatants needed to fool sophisticated traffic analysis.
Both Allies and Axis were really good at traffic analysis of intercepted signals. So good, in fact, that any serious operations needed to include wireless intercept deception. Basically, deny the enemy knowledge of your real intentions; deceive them into making false assumptions.
For example, Operation Overlord contained massive, multi-faceted deception. This included creation of fake armies complete with inflatable tanks, and fictional order of battle. All of these efforts were supported by double-agents and, of course, wireless intercept deception.
Leading up to D-Day, a ruse called Fortitude was created to convince Germans that the invasion would come at Pas de Calais. Starting three months beforehand, a special unit created a false network representing an imaginary army of 150,000 troops. The German T/A actually saw through this ruse but their High Command did not believe them . Once the Normandy invasion started, another wireless deception was implemented to convince the Germans that this was not the main operation. At the same time, aircraft dropped chaff to simulate another invasion fleet moving elsewhere on enemy radar. This was supported by fake wireless messages being sent by small boats below. So, German radar, intercept and direction finding were used against them. The following week, two Canadian warships were positioned on the west side of the Cherbourg peninsula, using scripted wireless chatter to simulate yet another imaginary landing force.
The Japanese used wireless deception at Pearl Harbor. They were aware that American T/A could identify and locate their carriers. They created false traffic which fooled the Americans into thinking the carriers were still in Japanese home waters, while the real ships moved towards Hawaii under radio silence. The original battle group radio operators had been transferred to create the false traffic back home. In preparing for the attack, Japan also did D/F and T/A on reconnaissance aircraft flying out of Hawaii. As a result, they discovered and exploited weaknesses in the surveillance.
Wireless Intercept Deception Techniques
Deception may be carried out with completely or partially false messages, radio silence, or wireless transmissions that simulate false locations, movements or intentions.
Technical analysis can be defeated by padding with fake messages or sending dummy messages to create false patterns in radio traffic. In order to work, T/A deception must be indistinguishable from normal traffic. So, just going radio silent will not defeat the enemy if that creates a new pattern.
The Allies got very good at having their wireless interceptors do T/A on their own traffic, and used this knowledge to create their deceptions. Attention to detail included varying transmitter power, and faking unique characteristics of known transmitters.
For voice communications, careful attention needed to be paid to accents and background noise. Usually, these were also scripted. In one case, a series of vans driving around an airfield, complete with sound effects, was used to simulate a false air force getting ready for an attack.
Other techniques included jamming, and impersonating enemy transmissions. Finally, the Americans would also plant false stories at broadcast radio stations, because it knew the Japanese monitored these extensively.