They could also blow up the tunnels and bridges into Manhattan and make it an island fortress. There are also ton of minor islands in North Carolina, South Carolina, Virginia, and Florida. Also, since the infection begins in Boston (fast infected cannot run forever or will wear out eventually), the U.S. government have time to be relocated to different places like Mount Weather, Site R, STRATCOM bunker in Offutt AFB, Nebraska (Bush stayed here during 9/11), Cheyenne Mountain Complex, or even an offshore carrier and submarine. Norfolk is just at D.C.'s next door. Greenbrier is already closed so Congress would be evacuated to Mount Weather as some of them were during 9/11.
- It seems that, using major transport axis, New York is at 350km from Boston. A human walk a 5km, and sprint at 10km/h, so you can safely assume that you have between a few days and two week before shit hit the fans in New York. That depend of a lot of parameters, like how is the stamina of the infected, but it's hard to give a precise estimation given we are by definition in ASB territory. Napoleon Grande Armée was able to walk 40km a day tho.
- In the meantime, the government will have to figure exactly what the fuck is happening (12 to 48hours ? ), define an action plan, mobilize the means to execute it and implements it. Evacuating millions of peoples in such a time, especially with most of the personnel available to carry such an evac being trained and briefed for it is, IMO, impossible.
- That’s what I think it’s impossible to save the North-Eastern metropolis. Massive deployment on nuke and chemical weapons (they are not zombies, so nerve gas should be more efficient than nukes) will work, but good luck to convince your government to deploy them on what will be still considered as your own civilians.
- Concerning safezones in the North-East, you’ll need to cram millions of peoples, without probably enough supply to feed them and personnel to control them. I might be mistaken, but they aren’t a lot of firearms in circulation in the zone, so relying on “militia” to plug the hole into your line of defense will be hard. Long Island seems to be savable, but you’ll again need to act very fast and “harshly” (ie blowing bridge with millions of people still crossing, trapped on the other side) and deploy enough military to maintain order until the infection “burn out” by itself (knowing that only a few infected going through might ruin your plans).
Then, I don’t see the US fall. It’s actually “easy” to contain the spread if the government maintain to keep control and act rationally:
- Releasing chemical weapons of the main infected concentration might be enough to reduce the hordes that will be roaming outside of the metropolis and avoiding the “problem” of fallout. Good luck dealing with the political fallout of collateral damage tho.
- If the Army act “smart” they can “lure” the infected in predefined killing zone, again removing a large part of the “large hordes”.
- For the isolated group/individuals that might go through, briefing the civilian about what to do (barricading themselves in upper floors etc…) might slow down the spread enough to have the situation controllable.
In the end, it’s also a question of logistic: will enough personnel, ammo, fuel, etc… be avalaible for deployement fast enough to contains the threat without the “social tissue” of the country collapsing and ruining any chance to maintain control? USA got some space to trade and more means than Britain, so I think there is a chance. No idea if the stopping line will be the Potomac, the Missipi or the Rockies tho.