How the US Military Made Your GPS Wrong on Purpose

Your GPS was once wrong on purpose — and the military can still shut it down in any region.

GPS wasn't built for Google Maps. It was built for war. So how did civilians get it — and how did the military protect itself?

GPS runs on 31 satellites with atomic clocks. Your phone trilaterates your position from their signal timings. But from 1990 to 2000, the military ran a program called Selective Availability. They deliberately dithered the civilian signal — up to 100 metres of error — so enemies couldn't use American satellites to guide weapons. Military receivers, though, used the encrypted P(Y) code, which ignored the dithering and kept the real position.

On May 1st, 2000, Clinton switched Selective Availability off — accuracy jumped from 100 metres to under 10. And it's gone for good: new satellites are built without it. But the military kept control — switching to regional denial, jamming GPS over one battlefield while everyone else stays sharp. Your GPS is global. Who gets to use it isn't.

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