Alright, I stayed up and read all of the book last night. It was somewhat compelling as a read, but very problematic in terms of the author's world view, understanding of model battles, and his lack of understanding and perhaps naive view of the military and military logistics.
I liked the Lost Regiment series quite a bit, though admittedly I was younger when I read it. The current "Destroyermen" series by Taylor Anderson is even better and Anderson is a gun nut.
Forstchen obviously has spent his time only with historical accounts of the military and perhaps teaching staff officers. This isn't without value, but he lacks an understanding of a good many things or else was mislead in his research.
While there is, or rather was, prepositioned military equipment overseas, a lot of it was expended already in the war on terror. If you want horror story matierial, delve into some of what our National Guard actually has on had to work with in the way of substitute standard back home and the three days of supplies, at best, that hospitals now have I suppose.
Anyway, "the entire Navy" as described in the book would be unlikely to come to the rescue. Carriers sitting in port, as a number are at any given time, only have a little bit on board in terms of food, bombs, etc. Unless one is just about to leave on a cruise, it isn't packed to the gills with supplies. It would also be arguable how much of the crew - much of which is ashore at any given time - would be willing/able to report. Esp if comms were out (you get a cell phone call via a phone tree to report), families weren't secured, etc.
While there are working tanks, Bradleys, etc afield in Iraq now, supporting them requires a lot of work. Basically, modern military gear, esp planes, relies on parts and maintenance that involve a lot of people, not only in uniforms, but contractors. Parts are made all over the world. Want to keep a plane running? Build some more bombs? Parts come from China, Taiwan, Japan, Korea... A member of the Japanese parliament pointed this out in Gulf War One - that American smart bombs wouldn't be working, let alone smart, without Japanese electronic components.
Anyway, moving even light infantry from point A to point B in brigade strength requires a major outlay on the part of the USAF in terms of capacity. Moving heavy forces, like armor, is even more complex. Abrams and the like don't get very far when their supply chain gets messy. They throw tracks, need engine overhauls, etc. Lacking a manufacturing base that is functional, they rather quickly become expensive pillboxes.
It would be even more unlikely for any American forces to return from Afghanistan, where supplies are tenuous and rely on large airlift abilities and the goodwill of Pakistan and Russia.
It's further naive to expect a functional chain of command and that units - which by the end of the book described as wearing piece work crazy quilt uniforms of various gear - would hold together under orders and become a stabilizing force instead of something more akin to "better give up some corn if you're within artillery range".
The town's leadership is a fascist enterprise since no one elected them, save the mayor, and she's essentially driven from power. A staff officer colonel that no one elects makes the decision to let a good bit of the population starve to get keep his troops (such as they are) fed. He mouths platitudes about America, yet they leave people to die outside the town - and make no effort to so much as organize refugee sanitation outside the town in addition to refusing more refugees. Yet the raiders are supposed to be worse, I suppose, for not making a pretense about what they're doing to survive...
Anyway... There's still a lack of understanding in the book about what it takes to actually get an EMP device of the type described into action. Essentially, it requires quite a bit of yield (a powerful, expensive, hard to make weapon) and an orbital launch capability. Despite the "this could happen" atmosphere - and it could - of hysteria that went with the book's publication, only a handful of nations have the ability to do this at the current time. The obvious culprit of such, China, is so heavily invested and dependent on the US as a market for their goods (if we were destroyed and couldn't buy Chinese crap, their own economy would collapse) as to make war unlikely.
The U.S. military itself either fields, or is soon fielding, a variety of EMP weapons of their own - mostly non nukes. An early one shut the lights out in Iraq as part of the shock and awe stage of thing some years ago, and this even showed up in early press report mentions (CBS, etc). This would lead many observers relying on open sources to think that at least some gear is shielded/tested. The PRC-77 for example apparently has seen this process take place, and the PRC-25 apparently mostly worked as well.
When Congress did testing, they found that things like semis, most vehicles (90 percent ish),trains etc still worked, though there would be problems with the power grid,switches of railroads, etc.
Shortwave radio would also still work, and there are quite a few sets operational in the U.S. and sitting in drawers, ammo cans, etc that would pick up international news feeds. Satellites on the other hand would be affected by an atmospheric detonation, so GPS and the like, necessary for our current global shipping needs would be a problem.