For a military operational area? Quite frankly I'm surprised that GPS signals aren't jammed today. At the very least, with the advent of cheap drones, and the dangerous payloads they can carry, I've got to believe that it will be forthcoming soon, regardless of the loss of intel that can be occurring.
The military created GPS. It wouldn't be very productive to jam their own signals on their own bases.
Military bases already have rules covering use of electronics like laptops, cameras, and phones, so adding smart watches to that list isn't very surprising.
