It was a different era. Most places allowed carry before the war, long guns especially, but openly worn handguns as well. (Not NYC of course, their anti firearms laws were older than that)
Civilian "militia" or "state guard", often composed of males too old or too young to enter the regular armed forces, patroled dams, power plants, and other "high value" targets. Many women were part of a network of aircraft spotters, at least on the coasts and in Hawaii. Early in the war civilian boats, yachts actually, were pressed into anti submarine patrol, as were private aircraft. Some of those yachts were even armed with depth charges, IIRC.
You know what? This sounds very do-able in this day and age. I'm betting that if things get any worse we would have very little trouble recruiting patriotic Americans to do this sort of thing. Liberals would stand in our way, of course--they'd do anything to stop this country from defending itself--but if we can manage al quaeda we can manage liberals.