| Summary: | Since the inception of the current hypersonic weapons arms race roughly two decades ago, many analysts and commentators have suggested that hypersonic weapons will increase the likelihood of conflict between the global superpowers. In this thesis, I provide an in-depth analysis of one variety of these concerns: that hypersonic weapons will increase the likelihood of nuclear war and incentivize nuclear arms racing. Two issues have prompted analysts to make this provocative prediction. One is that the United States' efforts to develop highly accurate, conventional hypersonic boost-glide weapons (HBGWs) may produce systems capable of conducting disarming strikes against US adversaries' nuclear retaliatory forces. This would enable the United States to increase its counterforce capabilities unhindered by its obligations under nuclear arms control treaties, and may therefore prompt its adversaries to do likewise
To evaluate HBGWs' efficacy as counterforce weapons, I assess the vulnerability of silo-based intercontinental ballistic missiles (ICBMs) to conventional hypersonic weapons. I find that such weapons may prove comparable to nuclear armed ballistic missiles in their efficacy as counter-silo weapons if they achieve the ambitious accuracy goals set forth for US weapons. They may also be able to achieve comparable kill probabilities against silos as nuclear ballistic missiles with the levels of accuracy that have been previously reported for hypersonic flight vehicles, though in a manner that would render them highly vulnerable to missile defenses. I therefore recommend that conventional HBGWs with intercontinental ranges be treated as strategically-salient weapons and subjected to numerical limits under arms control treaties.
The second issue is that, due to hypersonic weapons' ability to maneuver throughout flight, their intended targets cannot be determined with certainty. States could therefore misinterpret the intent of an attack. Of particular concern are attacks against conventional military forces being mistaken for counter-nuclear strikes or decapitating strikes, or an attack against one country being mistaken by a neighboring country for an attack against itself. Such misunderstandings could escalate conventional conflicts to nuclear war, or initiate hostilities between states not presently at war.
I find that, if states are unable to reliably detect and track incoming weapons, such misunderstandings would be highly plausible in many scenarios. However, if weapons can be reliably detected at least in the vicinity of high-value assets–such as strategic nuclear assets or national leadership–the risk of inadvertent escalation may be very low in most cases. I further find that providing for sufficient missile early warning coverage to minimize the risks associated with destination ambiguity is well within the capabilities of the preeminent nuclear powers. However, regardless of the extent of states' early warning coverage, I find attacks by HBGWs with speeds of roughly Mach 15 and above could still plausibly be mistaken for decapitating strikes if the target nation's leadership believes the weapons may be nuclear-armed. I therefore recommend states forgo HBGWs with speeds in excess of Mach 15 for conventional warfighting, establish no-fly zones for hypersonic weapons about their adversaries' capital cities, and that hypersonic weapons be exclusively armed with conventional payloads.
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