I always thought that the nuclear strike was designed to be step 1 in a Doomsday scenario--followed almost immediately by the application of weaponized smallpox

I always thought that the nuclear strike was designed to be step 1 in a Doomsday scenario--followed almost immediately by the application of weaponized smallpox and other biological agents. You can't really wipe out humanity with nuclear weapons (you can make a really good start of course), but if you smashed an areas ability to mobilize an effective response applying a biological agent immediately afterwards would allow a very deadly pathogen to spread unchecked.