I would definitely buy stock in a compass making company because we'd have to revert back to using maps and compasses.
What would happen to our Military if someone found a way to knock out our GPS system?
Without GPS we would return to "old school" methods. Tried and true.
We would still dominate!
We haven't had gps forever.
We fought and won without it and could again !
I'm sure the military has ways to navigate naturally, like I'm sure the navy has to use the stars.