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As early as the 1880s, the German intelligence services developed plans to sabotage railways and engineering structures in order to disrupt the mobilisation and concentration of the French armies. Many clues, intelligence reports and original documents were collected on this subject and testify both to the ingenuity deployed to design these plans and to the willingness to use all the new technical means to implement them. In the spring of 1914, a complete German destruction plan was drawn up using special agents called “U” agents. The French high command did not rule out this threat to their networks, which would not be without consequences for the smooth running of Plan XVII. Public opinion was also very much aware of this on the eve of the war. In order to prepare for this eventuality, a communications guard service (GVC) made up of soldiers and reservists from the territorial army was gradually set up and perfected from 1887 onwards. It was supplemented in 1909 by the Restricted Security System (DRS), which was to function from the period of political tension onwards. These measures contributed to the complete defeat of German sabotage at the beginning of the 1914 war.