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Automated counter attack systems exist already, at least to a degree [0]. Hypersonic weapons may make a first strike more feasible, but not that much. SLBMs with a depressed trajectory already have very short flight times [1]. The defenses against this apply to hypersonic weapons as well. The defenses being maintaining a survivable second strike capability in the form of a very stealthy SSBN fleet and a launch on warning posture.

Having lethal automated weapons systems is a scary idea, but hopefully we've already learned how to avoid using them for strategic deterrence.

[0] https://en.wikipedia.org/wiki/Dead_Hand

[1] https://www.scienceandglobalsecurity.org/archive/sgs03gronlu...