Recently in Bangkok RGP had the privilege of sharing some cold barley soup with a US Vietnam War veteran. He talked about collecting push-to-talk radio signals against the NVA and VC.
He said that in the very beginning of the war they had some success. He said that one develops a sixth sense, that something did not feel right. One night, he was feeling those little hairs on the back of his neck stand up, and so he went and turned on his radios and he noticed a very slight pop on one frequency, and so he waited. Once in a while he heard a small noise on that one particular frequency and so he just kept waiting, listening. He was in a small bunker with a candle, and the small noises became more frequent. Then he heard a word, just one word, but he did not recognize it. He said it was getting really late, and he just sat waiting, for hours. The enemy was moving and keying the microphone by accident as they moved up. He warned his Company Commander. He said the small noises got clearer and clearer, and then when the attack started the voice was so clear that it sounded like that VC soldier was right there in the bunker with him.