The Americans have form switching off the GPS or scrambling it.
At Zero Hour -1 of the First Gulf War, the British Battle Groups were on the start line in Saudi, ready to cross the berm into Kuwait.
Then all of the GPS signals became scrambled and unusable to everyone except the US Forces.
They 'forgot' to tell the Brits and other Coalition Forces.
Due to the type of terrain and it being dark, navigation was pretty difficult at the best of times and would have meant that the timings for the operation would slip.
Not good for all concerned.
Those were the days when the military weren't as heavily dependant on GPS as they are now...it was still in its infancy.
The Yanks were surprised to see the Brits set off on time in the right direction with accurate fire support, despite protestations at National level to get the GPS signal unscrambled.
How did the Brits achieve all their objectives on time in such a difficult navigation environment?
They grabbed a Naval Officer with a Sextant and stuck him ontop of a 432 to direct the lead elements navigation.