NWA SLF
the flight plan would become active at take-off and this message and the relevant times when to expect the aircraft at their area of responsibility is sent on to each ATC unit downline.
However, military centers would not care to look closely at something flying on an airway or outside of their boundaries. And unless they at least receive the data from the civilians they would not know which aircraft is not supposed to be there. And the coordination between the military and the civils does not work all too well in may countries.