US doesn't have a defense....The fallout from the missile blowing if you consider those aegis missiles a defense would kill pretty much everything in a 5-20 miles instantly and if you were looking that way your eyes would melt do to how bright and how hot it is....
The USA never had a defense other than the phrase "You nuke us we nuke you..."
Fun fact for the day: if one Nuclear warhead going the speed that North Korea's go, than we could shoot it out of the sky, but Hawaii might be screwed no matter what.
If nuclear war breaks out (I live in Texas) I'm going straight Northwest, maybe south if it gets that bad. I'll have filled up every container in my house with water, including all toilets and bathtubs. I will make currency into soda can TABS instead of Bottle caps, because there are alot more of those. I will also purposely expose at least one person around me to large amounts of radiation to see if ghouls are real. If they are, then i do the same thing to myself. I'll survive 200+ years as a ghoul! ANYWAY, me and my brainwashed army of super rednecks armed to the teeth will capture any remaining buildings and immediately clean them (something no one in falllout has apparently even thought of) I will also gather anyone and everyone who has said that they have problems with slaves or subjugating the community, they will either become slaves, be killed on the spot, or be used for breeding. In post nuclear holocaust we cannot survive unless we have dictatorships, at least in the beginning we will need groups like that of the book of Eli, all living together as one happy family, under the dictatorship of one man with a vision. I will, after all rivals have been dealt with, begin rebuilding the small town I set up shop in, first by securing a clean source of water, then be clearing as much rubble out as possible and recycling it in the new buildings. As my city grws I will begin work on a primitive aqueduct system using Salvaged gutters and PVC piping.