I know that when military aircraft operates in civilian airspace, that they need to file a flight plan just like any other flight, so that ATC can provide separation.
But if a military plane is flying near or over "hostile" territory (like a reconaissance plane, or a bomber) on a mission, then wouldn't it be possible that they might want the plane's flight path to remain a secret, or even the fact that such and such a plane is flying at all?
1. File no flight plan at all (is MARSA the right term?)
2. File a complete flight plan and trust that whoever gets to see it in ATC isn't working for the enemy and passing the info on.
3. File a partial flight plan that only covers the plane's flight route in "friendly" territory