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A secret broadcast is, simply put, a broadcast that is not for the consumption of the general public. The invention of the wireless was initially greeted as a boon by armies and navies. Units could now be coordinated by nearly instant communications. An adversary could glean valuable and sometimes decisive intelligence from intercepted radio signals: * messages that were not encrypted or poorly encrypted could be read * order of battle and future intentions could be deduced by traffic analysis * individual units could be located using direction finding In the 1920s the United States was able to track Japanese fleet exercises even through fog banks by monitoring their radio transmissions. A doctrine was developed of having units in the field, particularly ships at sea, maintain radio silence except for urgent situations, such as reporting contact with enemy forces. Ships in formation reverted to pre-wireless methods, including semaphore and signal flags, with signal lamps used at night. Communication from headquarters were sent by one-way radio broadcasts. =="Personal messages" on propaganda stations== During WWII, the BBC would include "personal messages" in its broadcasts of news and entertainment to occupied-Europe. Often they were coded messages intended for secret agents. Leo Marks attributes this idea to Georges Bégué, an agent for the Special Operations Executive who felt their use could eliminate a lot of the two-way radio traffic that often compromised agents. Such messages were also used to authenticate agents to sources of assistance in the field. The agent would arrange to have the BBC broadcast any short phrase the other person chose. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Secret broadcast」の詳細全文を読む スポンサード リンク
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