The military in the U.S. developed local GPS jamming techniques before turning off Selective Availability. SA was the deliberate, worldwide distortion of the GPS signal data to make GPS very inaccurate (off by as much as 100 meters), rendering it useless or even dangerous not only for the bad guys but also for many of the applications for which it is now being used. SA was added as an afterthough (like anti-spoofing encryption), after the military discovered that GPS was vastly more accurate than it had expected (15 meters, instead of 500). After effective local jamming techniques were developed, SA was permanently turned off.
For better or for worse, GPS is extremely easy to jam, which is one reason why it should not be relied upon as the sole means of navigation for aircraft. The military regularly conducts jamming tests in the U.S., and I'm sure jamming in active theaters is common, although obviously NOTAMs for the latter are not necessarily going to be published.
Galileo is another one of Europe's catch-up projects to try to show that it can do tech just as well as the U.S. On rare occasions, Europe is successful with such projects (e.g., GSM), but more often it just wastes taxpayer money and time while dozens of countries bicker endlessly with each other, turning practically every project into a political fiasco. It looks like Galileo may be going in that direction. And the idea of making people pay for something that is already free is highly illogical. Then again, pan-European projects like this often defy logic.