I'm currently looking at a world on the onset of a Zombie outbreak. The military and also the civilian population do not yet know that the dead are rising. Only the highest levels of command know about it.
The setting is in the US near a city where some scientists are inside and need to be extracted at all costs (as they possibly hold the key to a cure or to get it under control).
My first idea was that the characters would be Rangers with the orders to extract them.
"According to the rules that restrict the US Military from acting on US Grounds, what conditions are laid out that would allow them to break that rule?" The Posse Comitatus Act may have specific provisions in it or later attached to it that allow for when it may be violated
As such my question would be what could be a possible reason to involve rangers in that mission?