CASTLE ROCK is a reference to D-Day (today). I understand the symbolism to mean that a.) we have been infiltrated and taken over (i.e. France) and the day has come for Patriots to fight back with a massive response (i.e., 5,000 craft attack force) and begin taking the country (i.e. America) back from the Leftists (i.e. Nazis). There is a type or stone quarried in Caen France near Normandy that is used for building Castles and more.
https://en.wikipedia.org/wiki/Caen_stone