File:Communication Cable.jpg

English: This is an example of German signal wire that was picked up in the area of Vimy Ridge. It was common for a telephone or telegraph to use a single wire, with the return circuit laid through the ground. This meant that the signals could be detected on nearby wires, including those of the enemy. Specialized signals units listened to detect the "spillage" that escaped from the wires, and this was a valuable means of intelligence. To overcome this problem, telephone and telegraph lines used two wires, which were either twisted together or placed in a sheath. This formed a closed system that was much less prone to leakage.