“Right now, we are helpless.” Sen. James Inhofe’s (R-OK) recent remarks on the Senate Armed Services Committee made clear U.S. vulnerability to adversary hypersonic weapons—new weapons that travel at five times the speed of sound with the capability to deliver both conventional and nuclear payloads to U.S. targets and evade existing missile defense systems. This has prompted military planners, defense contractors, and research institutes to call for parallel capabilities to deter such attacks as well as concerns that the U.S. is falling behind its adversaries. Rather than adding fuel to the already considerable rhetorical fire surrounding hypersonics, this analysis considers the best case for U.S. investment in hypersonic weaponry. Then, it examines the potential drawbacks of developing hypersonic weaponry that are worthy of further examination as policy-makers consider the costs and benefits of continuing to invest in hypersonic weaponry. The Best Case for Hypersonics The best argument for the development of hypersonic weaponry is not the compunction to match an adversary—an eye for an eye—but rather as a result of a careful analysis of adversary capabilities and their impact upon the U.S. nuclear deterrent. In the event that adversaries develop capabilities that threaten the survivability of a U.S. second strike using existing ballistic missiles, gravity bombs, and air-launched cruise missiles (ALCMs), then hypersonic weapons might represent a viable avenue for reorganizing U.S. capabilities to offset dangers to the extant deterrence architecture. For example, adversary developments of missile defense capabilities more developed than our own might undermine the existing deterrence architecture and subsequently require capabilities that can evade these defenses, such as hypersonics. Proponents of hypersonics might also point to the increased flexibility provided such weapons—particularly in regional contexts—and the possibility that this will positively contribute to escalation control by providing a symmetrical response to any adversary attack—conventional or otherwise. What this best case should guard against, however, is the development of a capability for the sake of matching a strategic rival and without a clear use—either conventional or nuclear. In terms of strategic balance, it is the relative capabilities and the costs of achieving them and not the tools of warfare that ought to represent the subject of debate when weighing the instabilities introduced by a reinvigorated arms race. Hypersonic Weapons, Arms Race Stability, and Strategic Balance There are significant countervailing arguments against hypersonics that cast doubt on their contributions to strategic stability. Arms race stability, in which strategic competitors do not pursue arms racing behavior, has been theorized to lessen the risks of miscalculation and miscommunication that increase the likelihood of conflict. Proponents of arms race stability—a central component of strategic stability—also suggest that dangerous arms races can be avoided if technologies reinforce rather than undermine the mutual vulnerability that underpins nuclear deterrence. Hypersonics may uniquely undermine arms race stability in several ways. First, hypersonics have already been framed in terms of an arms race—driven in part by President Putin’s speech in March 1st in which he highlighted Russia’s program to develop a highly precise, long-range hypersonic missile and hypersonic warhead for its Sarmat ICBM system. China’s DF-ZF boost glide vehicle has achieved the most success in testing while India and France have been reported to be close behind. Second, hypersonic weaponry may prove useful for limited nuclear warfare and, therefore, reduce the threshold for nuclear use. Traditionally, nuclear conflict involving states well-developed nuclear capabilities would involve barrage attacks to overcome their respective missile defenses. Given their ability to overcome these defenses, however, hypersonic weapons provide a mechanism for a limited attack on nuclear adversaries. A number of scholars of nuclear deterrence going all the way back to Schelling in The Strategy of Conflict have argued that it is the massive nature of nuclear attacks that has hitherto deterred nuclear use and that limited nuclear options increase the risk of nuclear confrontation. It remains unclear whether this logic holds in cases of limited use. Third, hypersonic weapons are inherently dual-use—while not all hypersonics are nuclear, hypersonics can be nuclear—particularly as research and development continues to address the stresses placed on nuclear payloads. This reality complicates signaling to an adversary when hypersonic use is conventional rather than strategic in nature. To the extent that the discrimination problem is real, this may increase the risk that an adversary might mistake a non-strategic, conventional use of boost-glide technology for strategic, nuclear use and escalate the conflict accordingly. Taken together, hypersonic weapons may have a deleterious effect upon the strategic balance that policy-makers, academics, and politicians ought to consider as the United States decides to invest in the capability. A Hammer Without a Nail? Beyond the impact of hypersonic weapons on arms race stability and strategic balance, there are reasonable objections to hypersonic weaponry on a utilitarian basis that policy-makers might consider. Across each type of adversary that United States is likely to face, hypersonic weapons may represent a hammer without a clear nail. Over the course of the past two decades, prompt global strike capabilities—to include hypersonics—have been considered for a variety of targets from non-state actors in the wake of 9/11 to smaller, less-developed states to peer competitors. Following the failed test of a U.S. hypersonic weapon in 2014, for example, Anthony Cordesman of the Center for Strategic and International Studies suggested that hypersonic weaponry would be most useful against smaller, less-developed adversaries like North Korea and Iran. While hypersonic cruise missiles would undoubtedly prove effective against both terrorist groups and small state adversaries, existing standoff alternatives including Tomahawk Land Attack Missiles (TLAMs) and ALCMs arguably already provide adequate counterforce capabilities against these adversaries. Against states with little to no air defense assets, the additional maneuverability provided by hypersonic missiles is immaterial. Forward-deploying naval and ground-based assets may substitute for any delta in time between subsonic and faster hypersonic missiles if deemed necessary to deter a “bolt from the blue attack.” Moreover, the parallel proliferation of hypersonic technologies by less-developed states represents a risk to existing missile defense systems designed to protect the U.S. homeland. As a result, hypersonic weaponry does not appear to constitute a particularly attractive tool to address the threats posed by these types of actors. But what about peer competitors? Existing hysteria concerning hypersonic weapons is driven in large part by the reality that Russia and China enjoy an advantage in the development of hypersonic technology—at least measured by the number of successful hypersonic tests. China, for example, has had seven successful flights of the DF-ZF boost-glide vehicle while Russia successfully tested its Yu-71 hypersonic glide prototype in April 2016. The Yu-71 is part of Russia’s Project 4202 that is developing a hypersonic warhead for the new Sarmat heavy ICBM and is designed to overcome U.S. missile defense systems of the present and future. The second-strike capabilities that underpin nuclear deterrence between strategic competitors, however, remains largely unaffected by hypersonic weaponry—not least because the U.S. missile defense system is not designed to counter a strategic attack from a peer competitor. Indeed, a barrage attack from a peer competitor with existing ballistic missiles and warheads would overwhelm the U.S. missile defense system. While air- and ground-based deterrents might be held at greater risk by hypersonic weapons (or other existing capabilities), the sea-based leg of the triad would remain survivable in the event of their use. Thus, U.S. hypersonic weapons may have little effect upon the reality of nuclear deterrence that conditions behavior between the United States, China, and Russia. Opportunity Costs Policy-makers might also consider the opportunity costs of developing hypersonic weaponry. To date, the hypersonic weapon program in the United States has cost approximately $1 billion. Amidst a hefty nuclear modernization program, the development of this capability represents a significant opportunity cost. Calls to build hypersonic development into the program of record for modernization of the ground-based strategic deterrent (GBSD) to replace Minuteman IIIs are particularly problematic given the clear—rather than theorized—role of ICBMs in the strategic arsenal and the uncertain consequences of adding hypersonic technology to the program—particularly given past failures to develop military capabilities on time and on budget. At best, the United States develops a weapon system that it may not need alongside the GBSD system tasked with replacing its Minuteman III system. At worst, both GBSD and hypersonic weapons fail to materialize or suffer from delays that the United States can ill afford. Policy-makers must also balance the investments in hypersonic weaponry with the need to develop countermeasures to adversary hypersonic capabilities. STRATCOM’s Gen. Hyten, for example, has noted that next-generation, space-based early warning systems are needed to deal with an adversary’s development of hypersonic technology and sustain nuclear deterrence—not a tit for tat capability. Given that China and Russia are both developing hypersonic weaponry, these capabilities are of central importance. At the same time, ensuring survivability of the nuclear triad in the face of adversary hypersonic weaponry is of paramount importance rather than matching for matching’s sake. Puzzlingly, the concerns surrounding the ability of hypersonic weaponry to overcome missile defense have played an outsized role in arguments for developing U.S. hypersonic weapons—despite the vulnerability of these same missile defense systems to the existing capabilities of strategic competitors. U.S. missile defense capabilities comprised of satellite surveillance systems, radar systems such as the Sea-Based X-Band Radar, and SM-3, GBI, PAC-3, Aegis, and THAAD batteries are scoped to protect the United States against a small number of adversary ballistic missiles with simple countermeasures—not significant strategic conflict. Conclusion This article argues that there are substantial questions for policy-makers to answer as the United State weighs the inclusion of hypersonic weapons to its arsenal. While hypersonics may offer an attractive offset mechanism to adversary capabilities, there are clear questions concerning their impact upon arms race stability, utility, and the opportunity costs associated with developing them. In simple terms, the development of hypersonics ought not to be considered a foregone conclusion amid a broader conversation concerning U.S. strategic posture. All views expressed in this editorial are the authors own and do not necessarily reflect the views of the institutions with which he is affiliated. The author would like to thank Will Caplan, Bethany Goldblum, Ariel Petrovics, and Wes Spain for helpful comments. All shortcomings in the piece are the author’s own.