I think it's also worth noting that the physical infrastructure of certain portions of the circuit-switched AT&T Long Lines network (which also carried the AUTO

I think it's also worth noting that the physical infrastructure of certain portions of the circuit-switched AT&T Long Lines network (which also carried the AUTOVON network for the DoD) were designed, or at least attempted to be designed, to survive a nuclear strike. Theoretically traffic would have been manually re-routed around destroyed areas in a post-strike scenario. There's certain underground bunker sites on the historical L4 transcontinental coaxial cable routes which were designed with equipment mounted on springs, massively thick concrete walls, decontamination showers, and so on. Other mountain top and flat land area microwave point to point relay sites were designed to take a certain amount of overpressure and possibly would have survived nearby smaller nuclear weapon strikes (though obviously not a direct hit). Much of this pre-dates 1969 and the concept of the ARPANET. If you dig into things like what telecom services/links supported the NIKE missile batteries built around major cities and so forth. And what telecom services/medium to long distance links supported the data feeds from regional radar sites into the SAGE direction centers. Here's a fairly typical example of the more costly site of site, which you can see the photos of under construction and how much extremely reinforced underground concrete is involved. https://coldwar-ct.com/Home_Page_S1DO.html https://coldwar-ct.com/Home_Page_S1DO.html