Back in the day GPS was intentionally offset so countries couldn't use it for weapons.. well except it's owner of course!
> Because SA affects every GPS receiver in a given area almost equally, a fixed station with an accurately known position can measure the SA error values and transmit them to the local GPS receivers so they may correct their position fixes. This is called Differential GPS or DGPS.
https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_...
If you're a civilian doing surveying work, it was fine: you stick the base station at a known location, let it work for a few hours, and then you had high-precision GPS in that area. If you're a military power attacking someone on their own ground, it's not so useful. Even worse if you're at sea.