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 It's an interesting one, I think GPS is just packet data sent over a GHz frequency, they obviously can't kill that whole frequency though.
So can it be the individual handsets getting scrambled with something else? Is there a military frequency over writing the civvie stuff? But how is that controlled to one area?
Maybe they have a big device which hums all day long in the forest and sends out bogus signals?
It's way over my head but I'd be interested in hearing a laymans version.
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I know how it can be done with mobile phones as they have jammers that can block the signal but with a GPS it is coming from a satellite afaik unless A-GPS which also uses mobile signals I believe to get a quicker fix. Without that though your GPS still works off Satellites and the only thing I can think of that will stop an electronic device from working would be an EMP and I can't picture them doing that over a massive area of countryside?
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 The signal from the Satellite is incredibly weak a ground "satellite" could easily swamp a local receiver or alternatively send incorect timing info, throwing it off. The military have always had the capability of doing this, you will rememeber that the first civilian sets used to be less accurate than the military ones due to an error that was introduced to the signal. Later they developed systems to allow for battlefield interference, so that civilian sets could be disrupted, I presume that this is what they are using. A lot of army personnel are using shop bought kit, maybe it is to try and wean them off this stuff! Steve D
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Here is a thought. I know that GPS navigation was developed for the military, but I wonder where they now stand with regards to the extensive use made of the technology by civilian and commercial users? Never mind about us wandering about the hills, what about civilian emergency services, our police cars are tracked and managed using GPS, I presume the ambulance service does something similar. If an ambulance or Firetruck is late arriving to my home because the GPS system is disrupted, can I sue the army? I know of hundreds of boaters that rely on digital charts and GPS to navigate and it is very accurate indeed. My kit will tell me if I am in the right finger on the pontoon, that is accurate to within the length of the boat! Steve D
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 Pretty sure its the American army, and I'd be cautious about sueing them  Think they can block it at will though. Thats one of the reasons for the European Galileo thing.
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 If an ambulance or Firetruck is late arriving to my home because the GPS system is disrupted, can I sue the army? Do you think they could have made it to your home in the dark days before GPS? Anyway, the US can basically scramble GPS signals on a whim, but it isn't likely to happen these days, given the availability of alternatives (GLONASS right now, and the upcoming EU and Chinese sattelite constellations over the next few years). The MOD can and do use localised GPS jamming, but they tend to do it out in the sticks and give everyone a lot of warning ahead of time. They've already halted one jamming exercise due to protest from fishermen, who can better justify their need for GPS than road users.
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I know that they managed before GPS, but the fact is that we rely on it now, we managed before mobile phones and computers as well! Steve D
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 in the first oil driven desert foray the merkin military didn't have enough gps units to go round. so they issued the troops with garmin units. not much use introducing errors when your own troops are using the equipment. so they switched the errors off. that drove localised jamming developments. as a matter of global largesse, i.e. the military no longer needed to introduce errors into the signal as they extensively used "consumer" units, they bigheartedly switched the errors off permanently. gps is owned by the merkin military so in theory they can do what they want with it - just as any privately owned or government owned system can. jamming is just switching the volume up on something to drown out the neighbours dog barking. the gps signal is very, very weak. the units are quite marvellous what they can do. the signal is around 100w from 20,000 odd miles away. so it's fairly easy to swamp a signal. gps accuracy is further enhanced by ground station broadcasts. and as i love a good conspiracy theory are there actually military only gps satellites up there?
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The chances of GPS being switched off by anyone is pretty remote - if only because of all the emergency services across the globe that now depend on it, not to mention all the "tracking" devices in use by the likes of cash handling companies etc. As for jamming - given the strength of the signal - doesnt take a lot especially if the aim is not to blank out the satellite signal, just to confuse the reciever and make it unuseable. There are (I think) some military only frequencies, but there is no mention anywhere of military only satellites
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and as i love a good conspiracy theory are there actually military only gps satellites up there?
I don't know, but the UK military communications satellites are part of skynet 
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