Uh, it's not exactly a secret that FEMA has a think tank group that sets up protocols to counter any possible scenario that would constitute an existential threat to the United States, its government and larger population centers (nukes, nerve gas, tornados, asteroids, conventional military invasion,etc). They even have one for a zombie apocalypse that serves as a demonstration of what one of those protocols would look like. You can even download a PDF of it if I remember it correctly.