Irrespective of nuclear war the design goal was always to create a network of redundant nodes across wide geographical dispersion. That solves two problems: 1

Irrespective of nuclear war the design goal was always to create a network of redundant nodes across wide geographical dispersion. That solves two problems: 1. Increases network durability. 2. Allows uninterrupted participation by geographically separated parties. This is a hallmark of military technology still very much in use today and it goes as far back as the mid-1860s when the new US Army Signal Corps began experimenting with and integrating into conflict locations the first electronic communication technologies. Geographically dispersed redundancies are still import to military communications. On a tactical level this typically involves things like radio relays on hilltops, tropospheric shots, and various line of sight technologies. On the strategic level it involves having multiple routes through the internet over different kinds of physical media moving in different geographic directions. You don't see this as much in the commercial world, because sending network traffic through less efficient routes is slow and costly, so redundancies are only an emergency fallback. From a military perspective the network will go down at any moment, so slow and expensive are still favorable to disconnection. As a result the military will eagerly employ many layers of many redundant options. Cost is a less significant factor for the military since they are the only ones to own all layers of their own stack and thus able to operate in isolation.