- The name “hypersonic missiles” is misleading, because speed is not the differentiating characteristic of these weapons. Hypersonic missiles are not necessarily faster than normal missiles.
- In principle, the key difference between hypersonic and ballistic missiles is their flight altitude and lateral maneuverability, which makes detection and target prediction more difficult. In practice, the accuracy and maneuverability of current hypersonic missiles remains uncertain.
- Hypersonic missiles are not unique in their ability to overcome missile defenses. Missile defenses are ineffective; they cannot reliably intercept normal missiles.
- I think inaccurate memes about the capabilities of hypersonic weapons are a non-trivial driver of attention and funding. We could correct notable voices (e.g. the NYTimes article) which fail to mention that regular missiles can penetrate missiles defenses too.
- The biggest uncertainties in this space seem to be the maneuverability and accuracy of current hypersonic missiles, and forecasts for these capabilities. The extent to which the build up of hypersonic hypersonic missiles represents an unusually risky arms race vs. “regular” acquisition of new capabilities remains unclear.
- I spent ~15 hours producing this report, so I expect many errors.
Why care about hypersonic missiles?
In 2018, US undersecretary of Defense Michael D. Griffin said hypersonic weapons were his number one priority. In June 2019, the New York Times ran an article titled “Hypersonic Missiles Are Unstoppable. And They’re Starting a New Global Arms Race”. In December 2019, Russia said it possessed hypersonic missiles and had placed two into service--the first country to do so. Around the same time, China exhibited hypersonic missiles; these missiles are expected to be operational in 2020. In March 2020, the US said it successfully tested an unarmed prototype. The US FY2021 budget for hypersonic programs is US$3.2 billion (up from 2.6 billion in 2020), and its stated goal is to possess a deployable missile by 2023. France, India, Australia, and Japan are also developing hypersonic technologies.
Hypersonic weapons, like other missiles, are destructive in and of themselves. Additionally, they may be a “destabilising technology”, one that increases the likelihood of great power conflict. Some people have characterised ongoing hypersonic development by the US, Russia, and China as an arms race. In his most recent podcast with 80K, Will MacAskill mentioned hypersonic missile policy as something we know very little about but “should be looking into”.
Investigating hypersonic missiles may speak to broader issues related to arms races, Sputnik moments, and how certain technologies become perceived as not “just another technology”.
Types of hypersonic missiles
There are two variants of hypersonic missiles. Hypersonic glide vehicles (HGV) are boosted upward by conventional ballistic missiles or rockets, then “skip” between layers of the atmosphere--like a stone on water--before diving directly towards the target. Hypersonic cruise missiles fly horizontally under the power of a scramjet. HGVs receive almost all of the funding and attention now.
Hypersonic missiles are often defined as missiles that can travel faster than mach 5, or 5x the speed of sound. I find this misleading, because ballistic missiles also travel at hypersonic speeds--they fly at mach 20. Hypersonic missiles fly at mach 10–30. For example, Russia’s Avangard missile apparently has a top speed of mach 27 and average speed of mach 10. So hypersonic missiles are not necessarily faster than ballistic missiles.
The key difference between hypersonic and ballistic missiles is their altitude and maneuverability. Hypersonic missiles fly lower than ballistic missiles, which delays detection time by ground-based radar. In addition, hypersonic missiles may be capable of moving laterally mid-flight, which makes targets harder to predict. In contrast, the target of a ballistic missile is predictable from its launch trajectory.
However, defense analysts have questioned the maneuverability and accuracy of current hypersonic missiles, especially long-range models. The friction and heat generated by atmospheric flight creates problems for navigation and electronics. Designing the right shape and materials to manage these problems remains a major technical challenge.
Implications of speed and trajectory
Assuming they work, hypersonic missiles compress the response time available to decision makers and create uncertainty about intended targets, plausibly increasing the risk of miscalculation or unintended conflict escalation. These issues are exacerbated by warhead ambiguity--the US says that their hypersonic missiles will only carry conventional payloads, while Russia and China say theirs are nuclear-capable.
Some sources claim or imply that hypersonic missiles are “game-changing” because they give possessors the ability to overcome otherwise robust defences. The NYTimes article says “there are no surefire defenses…[hypersonic missiles] are fast, effective, precise and unstoppable”. Both Russia and China seem to be developing hypersonic missiles in response to US ballistic missile defense programs. In 2018, Putin said that US anti-ballistic missile systems are improving, and “if we do not do something, eventually this will result in the complete devaluation of Russia’s nuclear potential”. In other words, Russia and China are pursuing hypersonic missiles as an assured means of penetrating US missile defenses.
The thing is, US missile defenses are not otherwise robust. The US has spent more than US$200 billion on missile defense since 1983, but according to Thomas P. Christie (DoD director of Operational Test and Evaluation from 2001–2005) current defense systems “haven’t worked with any degree of confidence”. A major unsolved problem is that credible decoys are apparently “trivially easy” to build, so much so that during missile defense tests, balloon decoys are made larger than warheads--which is not something a real adversary would do. Even then, tests fail 50% of the time. Andrew W. Reddie adds that US anti-missile defenses are aimed at North Korea and Iran, not Russia and China. US deterrence is based on assured second strike, not the ability to block incoming attacks.
Andrew Cockburn says that hypersonic weapons are a case of “[developing] weapons that don’t work to meet threats that don’t exist”. During the cold war, for example, US accumulation of missiles was originally justified with the non-existent “missile gap”. According to Cockburn, this phenomenon is partly driven by defense industrial dynamics in the US and Russia. In addition to the capabilities of weapons, countries develop weapons for reasons including national pride and pork-barrel politics.
Arms race dynamics
Weapons may be less effective than claimed, and still have implications for international relations. Whatever the actual capabilities of hypersonic weapons, they are currently perceived as crucial by the US, Russia, and China. All three countries will likely possess these weapons by mid-2020, just as major arms-control treaties are being dismantled. There are currently no major discussions about limiting hypersonic weapons. The build-up of weapons which are perceived as important may erode wider cooperation and trust between countries.
I observe some inaccurate memes about the capabilities of hypersonic weapons, especially their ability to overcome otherwise robust defenses. Many popular media articles fail to clarify that ballistic missiles also achieve hypersonic speeds. The differentiating characteristic of hypersonic missiles--their maneuverability--is not fully solved.
These memes, though inaccurate, likely contribute to current attention and funding directed at hypersonic weapons. Names matter--I speculate hypersonic missiles would receive less attention and funding if they were called “maneuverable missiles”. It helps that missiles are a tangible and discrete product, as opposed to, say, electronics. The build-up of hypersonic missiles may increase adversarialism in international relations.
It seems robustly good to correct voices (e.g. the NYTimes article) which say that hypersonic missiles are unique in their ability to penetrate missile defenses and are thus a “game-changer”.
 However, the DoD has been inconsistent about its top priorities. See The Defense Department Needs a Real Technology Strategy by Paul Scharre (2020).
 R. Jeffrey Smith, ‘Hypersonic Missiles Are Unstoppable. And They’re Starting a New Global Arms Race.’, The New York Times, 19 June 2019, sec. Magazine, https://www.nytimes.com/2019/06/19/magazine/hypersonic-missiles.html.
 Kelley M Sayler, ‘Hypersonic Weapons: Background and Issues for Congress’, 2020, 26; Kelley M Sayler and Amy F Woolf, ‘Defense Primer: Hypersonic Boost-Glide Weapons’, 2020, 3.
 Destabilising technologies disturb the current equilibrium where countries lack sufficient incentive to initiate conflict. Toy example: A is deterred from attacking C because C can strike back. If hypersonic missiles are perceived to erode C’s second-strike ability, then A is less deterred from attacking. In turn, C has more incentive to launch a preemptive attack, and so on.
 Roughly, moments when a technological achievement by a competitor spurs a country to greater activity. In the context of AI development, for example, AlphaGo has been called a Sputnik moment for China.
 Richard Garwin, ‘Technical Aspects of Ballistic Missile Defense’, 1999, https://fas.org/rlg/garwin-aps.htm.
 Kyle Mizokami, ‘Hypersonic Missiles Just Aren’t Accurate’, Popular Mechanics, 10 March 2020, https://www.popularmechanics.com/military/weapons/a31295238/hypersonic-missiles-accuracy/; David Axe, ‘Is Kinzhal, Russia’s New Hypersonic Missile, a Game Changer?’, The Daily Beast, 15 March 2018, sec. world, https://www.thedailybeast.com/is-kinzhal-russias-new-hypersonic-missile-a-game-changer; Andrew Cockburn, ‘Like a Ball of Fire’, London Review of Books, 23 February 2020, https://www.lrb.co.uk/the-paper/v42/n05/andrew-cockburn/like-a-ball-of-fire.
 Ballistic missiles avoid these issues because they spend most of their flight in low-earth orbit.
 Sayler and Woolf, ‘Defense Primer: Hypersonic Boost-Glide Weapons’: “Unlike Russia and China, the United States is not developing HGVs for use with nuclear warheads” (p1).
 Smith, ‘Hypersonic Missiles Are Unstoppable. And They’re Starting a New Global Arms Race.’
 Team of the Official Website of the President of Russia, ‘Presidential Address to the Federal Assembly’, President of Russia, accessed 13 May 2020, http://en.kremlin.ru/events/president/news/56957.
 Cockburn, ‘Like a Ball of Fire’.
 Andrew Reddie, ‘Hypersonic Missiles: Why the New “Arms Race” Is Going Nowhere Fast’, Bulletin of the Atomic Scientists (blog), 13 January 2020, https://thebulletin.org/2020/01/hypersonic-missiles-new-arms-race-going-nowhere-fast/.
 Sayler, ‘Hypersonic Weapons: Background and Issues for Congress’.