Comment by Taniwha

I remember old timer kiwi radio hams telling me (literally) war (WW2) stories of people laying earth return phone lines (ie a single insulated wire with a watered earth stake for a return path at each end) - they were laid along the front in North Africa for RF-free communication.

At one point someone rung down the line and was answered "jawohl?" ..... hung up immediately ..... seems the germans were doing the same thing, path of least resistance was the 2 copper wires ... they found a German speaker to listen in until the front moved

Those old timers told some great stories, don't know how true this one was, it's at least plausible