RM390,

The GPS System would not have to be "Shut Down" just switched over
to an {Encrypted} Signal.

Civilian 'users' would be temporally "Locked-Out" of the GPS System.
[ They Would Be - "Lost In Space" ]
http://www.virtualheartland.com/lost...axy/index.html

"Only" the US Military certain Federal Agencies would have the
necessary equipment to }Decode{ the GPS Signals.

..
warning, Warning. WARNING ! Will Robertson ~ RHF
http://www.virtualheartland.com/lost...ghts/Robot.htm
..
..