What’s the big deal about hypersonic missiles?


  • 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.[1] In June 2019, the New York Times ran an ar­ti­cle ti­tled “Hyper­sonic Mis­siles Are Un­stop­pable. And They’re Start­ing a New Global Arms Race”.[2] 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.[3]

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.[4] 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[5], 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.[6] 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.[7] The fric­tion and heat gen­er­ated by at­mo­spheric flight cre­ates prob­lems for nav­i­ga­tion and elec­tron­ics.[8] 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.[9]


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”.[10] 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”.[11] 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”.[12] 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.[13] US de­ter­rence is based on as­sured sec­ond strike, not the abil­ity to block in­com­ing at­tacks.[14]

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”.

[1] How­ever, the DoD has been in­con­sis­tent about its top pri­ori­ties. See The Defense Depart­ment Needs a Real Tech­nol­ogy Strat­egy by Paul Scharre (2020).

[2] 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.

[3] 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.

[4] 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.

[5] 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.

[6] Richard Gar­win, ‘Tech­ni­cal Aspects of Bal­lis­tic Mis­sile Defense’, 1999, https://​​fas.org/​​rlg/​​gar­win-aps.htm.

[7] 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.

[8] Bal­lis­tic mis­siles avoid these is­sues be­cause they spend most of their flight in low-earth or­bit.

[9] 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).

[10] Smith, ‘Hyper­sonic Mis­siles Are Un­stop­pable. And They’re Start­ing a New Global Arms Race.’

[11] 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.

[12] Cock­burn, ‘Like a Ball of Fire’.

[13] 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/​​.

[14] Sayler, ‘Hyper­sonic Weapons: Back­ground and Is­sues for Congress’.