Canal Defence Light
On the surface, the Canal Defence Light, which was invented by the British, seems kind of dumb: it’s just a big light bulb on top of a tank. But, when a special shutter was operated that opened and closed six times a second, it produced a strobing pattern that made it actually impossible to see the tank.
In multiple tests, gunners tried to fire on tanks equipped with the CDL but were unable to hit it. The same technology has evolved into immobilization devices like the one being developed by Peak Beam, but for some reason the CDL wasn’t ever deployed on the battlefield despite its impressive results. Can you imagine the terror of seeing a tank bearing down on you, guns blazing, and you being incapable of landing a single shot in response?