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Rubber Tanks and Sonic Trucks: the Ghost Army of World War II (hackaday.com)
szczys writes: While you may have heard of the Ghost Army that was used to fake troop movements during WWII, it's unlikely that you truly grasp the level of skill and success these elite groups achieved. At its surface, the story is about inflatable armies that could fool German intelligence from afar. That is one visual component, but there were many more involving sound and radio communications. Before the digital age, it was quite a trick making authentic audio recordings of military vehicle sounds on 2-mile long spools of very thin wire played back from vehicles outfitted with 500 Watt speakers. The A/V wasn't complete without radio communications spoofed to look like the Ghost Army was the real deal: this used the best of personal-morse-code-style impersonators. Elite groups trained in these phony arts operated throughout the European theater. Their story was top secret long after the war because the craft was considered a strategic asset well into the cold war era.
Probably a really good thing that they ran, as they would have been dramatically outnumbered if they'd hung around to 'fight'.
Keep in mind that this was a couple of guys in a vehicle pretending to be a whole battalion. So any attack on them would have been made by a force big enough to have some chance of success against the much larger 'illusory' target.