You see this warning on all WWII German transmitters, but where did this warning originate?
The answer is World War One.
In the first month after the German invasion of France in 1914, wireless communications were extensively used by the Germans. Certainly the lack of adequate organisation, discipline and security permitted the French to counter most German tactical operations, which finally culminated in the "Miracle of the Marne", where the German military progress on the western front was ultimately stopped. After this turning point in history, the western front began to stabilize and the construction of telephone facilities increased day by day on both sides of the front line.
To economize on the construction of telephone lines (wire), most short distance lines were asymmetrically built, so that only one signal wire had to be deployed, and the ground (earth or soil) was used for the return circuit.
Its simplicity of deployment and operation is obvious, but from the perspective of security such a telephone circuit was a real nightmare. All belligerents were employing so-called "search electrodes" which were stuck into the ground to look for any kind of modulated electrical earth currents.
The answer is World War One.
In the first month after the German invasion of France in 1914, wireless communications were extensively used by the Germans. Certainly the lack of adequate organisation, discipline and security permitted the French to counter most German tactical operations, which finally culminated in the "Miracle of the Marne", where the German military progress on the western front was ultimately stopped. After this turning point in history, the western front began to stabilize and the construction of telephone facilities increased day by day on both sides of the front line.
To economize on the construction of telephone lines (wire), most short distance lines were asymmetrically built, so that only one signal wire had to be deployed, and the ground (earth or soil) was used for the return circuit.
Its simplicity of deployment and operation is obvious, but from the perspective of security such a telephone circuit was a real nightmare. All belligerents were employing so-called "search electrodes" which were stuck into the ground to look for any kind of modulated electrical earth currents.
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