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Example: Gen. Mark Milley calls China's hypersonic weapon test 'very concerning'

If we currently have mutually assured destruction (MAD) where nobody can fire nuclear weapons because the other side can retaliate and wipe both parties out, then why do these hypersonic weapons matter? It just means that China has joined the MAD club. The only practical restriction is that none of the already-established MAD club members can fire nuclear weapons at China.

Neither of the two obvious explanations I can see are very appealing:

  • The US was intending to fire nuclear weapons at China, so China's newfound ability to retaliate is not welcome (and China calling the US bellicose is fully justified).
  • The US doesn't believe in MAD, and we are all fantastically lucky there hasn't been a nuclear war yet.

Cynically, there is also:

  • The US doesn't actually care. Only the US military does, because if they can get the rest of the US to care, they'd also receive more funding.

I am wondering which, if any, of these are the right explanation.

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    The official explanation is that hypersonic weapon are impossible to stop: time.com/6108450/china-missile-test-reported-significance. Specifically Time writes: "The U.S. currently has no way to stop such a weapon, especially if it were maneuverable".
    – markvs
    Oct 29 at 6:32
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    If you can fire something fast and unstoppable at other people's missile silos, mutual destruction might become a lot less assured, and thus less of a deterrent to nuclear war. Oct 29 at 7:40
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    @EikePierstorff as I understand it, that's why a lot of nuclear deterrence is submarine-based: even if you destroy the other side's entire country, you can't destroy their submarines which are somewhere in the oceans, and they can retaliate.
    – Allure
    Oct 29 at 7:44
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    @markvs doesn't the US also currently have no way to stop a full fleet of ICBMs by any of the other MAD club members?
    – Allure
    Oct 29 at 7:45
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    You could add: why does the US care so much about China's when Russia has already deployed Avandard.
    – Fizz
    Oct 29 at 10:18
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Hypersonic weapons threaten Mutual Assured Destruction by allowing possible decapitation strikes

In order for Mutual Assured Destruction to work, the side who has been attacked must be able to retaliate symmetrically against the attacker. Hypersonic weapons give an advantage to whoever can use them in a first strike, making a second strike less effective. If second strikes are no longer effective, you no longer have MAD.

I note in your comments that you point out that second strike capability could be preserved by submarines. That kind of strategy can work very well if you are a country that can effectively deploy ballistic missile submarines at large scale to launch a second strike that will destroy China, e.g. US or Russia. It doesn't work very well if you aren't such a country and aren't directly aligned with US or Russia, like India (who only has one such submarine).

A world where China is only constrained by MAD is actually a lot more dangerous

China has stated their intent to invade Taiwan for decades. China has not invaded Taiwan in part because of the United States policy of strategic ambiguity that heavily implies US would go to war with China if this happens. Hypersonic weapons would change how this war could happen by making it necessarily involve a nuclear exchange between China and US as the opening move. Most Americans are not in favor of being reduced to ash over some island in Asia, so that would presumably make US less likely to intervene, and therefore China to be less deterred from invading Taiwan than it is today.

Nobody officially believes in MAD anyway

Historically, neither the US nor the USSR officially adopted MAD as part of their policy on nuclear weapons. The official Soviet policy was that nuclear wars were survivable and therefore winnable, which contradicts MAD. Official US policy at several times included the possibility of limited nuclear strikes that would not necessarily entail mutual destruction (e.g. "tactical" nuclear strikes to blunt potential Soviet armored advances through the Fulda Gap).

Chinese views on MAD are less well understood, in part because China's nuclear policy is changing in ways that are less well understood. There are indications that Chinese military leadership is not interested in having large nuclear arsenals like the US and Russia. Instead, they would like to have a smaller arsenal that is more technologically sophisticated, and tailored specifically for threats that China wishes to counter. That would imply a rejection of the MAD framework as it has been traditionally understood.

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    I would question this. The cornerstone of MAD is second-strike capability -- i.e. I know you can take me out, but if I go, you go too. Prevention of enemy first-strike of various kinds, is a higher standard than MAD. Preventing an enemy strike entirely opens the door to one's own use of tactical nuclear weapons as a "means of persuasion" (to phrase it in an entirely amoral way), since there would no longer be fear of escalation by the other side.
    – Pete W
    Oct 29 at 15:13
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    @PeteW If you strike first to prevent the enemy from striking, then the enemy's prevented strike is the second strike typically discussed by MAD.
    – Joe
    Oct 29 at 16:11
  • It doesn't work very well if you aren't such a country and aren't directly aligned with US or Russia, like India (who only has one such submarine). Wouldn't this justify India being concerned about China's hypersonic weapons, but not the US?
    – Allure
    Oct 29 at 16:23
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    @Joe - right, that's one way to defeat a second strike, by identifying ALL the enemy's launchers and taking out ALL of them in one move. My understanding is that this is considered unrealistic for a large country, due to road-mobile launchers (which are indistinguishable from potentially much more numerous decoys), and of course submarines. It was hoped/feared that the less unrealistic way to defeat a second strike capability was with ABM. My unerstanding is that this, not a winning first-strike, was the motivating scenario, and it even resulted in the now defunct ABM treaty.
    – Pete W
    Oct 29 at 16:47
  • @Allure I'm sure the 330 million citizens of the United States who could be annihilated in a Chinese first strike would find the submarine launched second strike a very cold comfort.
    – Joe
    Oct 29 at 18:09
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Hypersonic glide vehicles like Russia's Avangard (already deployed in small numbers) present the problem of unpredictable target/trajectory:

“If you’re going Mach 13 at the very northern edge of Hudson Bay, you have enough residual velocity to hit all 48 of the continental United States and all of Alaska. You can choose [to] point it left or right, and hit Maine or Alaska, or you can hit San Diego or Key West. That’s a monstrous problem,” Paul Selva, the former Vice Chief of Staff, said last year.

The US is funding some reseach programs how to shoot them down such as "Glide Breaker", but given the level of funding (a dozen million $) they're in the early stage. At more advanced stage (i.e. billions are being spent already), but not yet complete are space-based "cold" sensors that might detect hypersonic vehicles in flight, such as the "Next-Gen OPIR" currently being deployed, but the deployment schedule of which (stretching to 2029) apparently has the Pentagon uneasy.

What China has tested recently is not entirely clear though. Some speak of a FOBS-like system instead... which somewhat more roundabout than merely launching a missile that goes directly in the general direction of the enemy, even with hypersonic glide. A FOBS enters partial orbit and can e.g. go around the south pole to hit the US rather than from the usual general direction that an attack would be expected from a know adversary.

The weapons [...] were meant to counter the U.S. Safeguard missile defense system. Safeguard was designed to use Spartan and Sprint missiles to shoot down Soviet warheads targeting U.S. ICBMs. The Soviet Union would use FOBS to target the system's radar network from the rear, rendering the ICBMs vulnerable again.

The U.S. government canceled Safeguard in 1975, and the Soviet Union retired its FOBS weapons in 1983. Since then, none of the world's nuclear powers have considered FOBS useful enough to field an operational system.

In September, incoming Secretary of the Air Force Frank Kendall made an oblique reference to a Chinese FOBS system, describing Chinese advances in missile and space technology. He specifically mentioned the FOBS concept—though he did not actually come out and say definitively that China conducted a test.

According to The Economist, China has possibly tested a G-FOBS, i.e. FOBS launching a hypersonic glider, or in more prosaic terms "space shuttle with nukes"

China’s tests, however, involved a twist. The gliders did not simply go up and coast down, but also circled the Earth in space. This is similar to the approach employed by the Soviet Union’s Fractional Orbital Bombardment System—fractional because it did not involve a full revolution around the Earth—which was deployed between 1969 and 1983. The advantage of an orbital weapon is that it can go over the South Pole and reach America from a direction where the country has neither ground-based radar nor perfect coverage from infra-red satellites that can spot rocket engines.

The combination of orbiter and glider is not in itself new. America’s old space shuttle and its current X-37B spaceplane are examples of things that are sent up by rocket, go into orbit and then glide back. The difference is that the shuttle was not built to crash to the ground with nukes attached. China appears to be the first to turn this combination into a prototype of a weapon, says Tong Zhao of the Carnegie-Tsinghua Centre for Global Policy in Beijing.

Speaking of MAD, the US has some 44 ICBM interceptors in Alaska and California, and 20 more have been budgeted this year. China has only like 110 ICBMs seemingly with 185 warheads. News as of this June was that China was building 145 to as many as 250 more ICBM silos, although just like the US does, analysts expect China will play a "shell game" and not stock every one of them with a missile.

According to a 2020 study by a Chinese academic, until the year 2000, China had basically no chance of any retaliatory nuclear strike against a fist stirke by the US, which had the capability to preemptively destroy all Chinese nuclear weapons (including submarine based). US analysts were basically in concurrence with this assessment. The Chinese academic put the probability that China could have hit back with just one warhead at 0.3-1.6%, depending on the readiness level of the Chinese forces. With the deployment of (about 100) road mobile ICBMs by China, in 2010, it had managed to attain a 38-90% chance of striking back with one warhead, 4-37% with three warheads, and 1-6% with five. The small number of warheads however was assumed to be a serious problem in the face of increasing US interceptor numbers. According to this model, the US can afford to fire four interceptors at every Chinese warhead that would have survived a US first strike.

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China already has ICBMs that are capable reaching the entire USA, although in limited numbers and they'd need to be located in the more eastern areas of China, so in one sense low earth orbit hypersonic missiles aren't massive leap forwards in China's nuclear deterrent capability. But that might be a somewhat simplistic view.

Firstly, the US has leaned towards the idea of developing an anti-missile shield, and withdrew from the anti-ballistic missile treaty in 2002 to enable it to pursue this goal. It is of questionable value against the hundreds or thousands of ICBMs that Russia could launch in a full scale strike, but China is estimated to only have 20-40 ICBMs capable of reaching the US (although Fizz's answer has much more up to date and reliable data on China's ICBM capability). Allowing for malfunctions, misses and successful intercepts, it's conceivably that the US could survive a Chinese strike with heavy but far from overwhelming damage.

There is also the factor that China's existing ICBMs are at the limits of their range in hitting the US mainland, which means launching from close to the Chinese east coast, and potentially being more vulnerable to boost-phase interception from ground based systems in e.g. Korea, or sea based systems.

A delivery vehicle that can be launched to orbit the earth one or more times before choosing a target can obviously be launched from just about anywhere in China, well out of range of any boost-phase interception.

A second factor is that hypersonic missiles obviously move faster than older ICBMs, at least at some points in the trajectory (arguably any missile getting close to low earth orbit is moving at roughly orbital speed at its midpoint). Faster moving targets are harder to hit and thus less likely to be intercepted, making any USA missile defense systems less effective - although it is unknown how effective they'd be in any case.

Thirdly, no-one really knows what a technological advantage will mean in practice until it is used in anger. It wasn't obvious to anyone when the Wright brothers made the first powered flight that less than 40 years later the aircraft carrier would render the battleship obsolete. It wasn't obvious to many people how the invention of the machine gun would completely change infantry warfare. It wasn't just a faster-firing gun. It completely changed how infantry engagements were fought, and was the death-knell of mounted cavalry. When the tank was invented, most just saw it as a mobile pillbox. Very effective, but primarily in support of the infantry. But then Germany showed that it opened up a completely different kind of mobile warfare that no-one had any idea how to counter at first.

So maybe hypersonic missiles will be as relevant as 3-D cinema - gets lots of headlines for a while but makes no difference. Or maybe the added capability is itself enough to make a critical difference. Maybe it enables anti-satellite capabilities in a previously unmatched way, enabling nations to wipe out the space-based intelligence gathering, communication and GPS capabilities of an opponent. Whether it will turn out to be a difference maker like that is hard to say.

Of course there is always another factor to consider (aside from the one in the question about the military just agitating for funding). The USA is obviously moving very much in to a 'containing China' strategy, and as such it is politically necessary to talk up the threat that China poses to US interests. Russia and North Korea have previously tested hypersonic missiles (I don't know how believable NK's claims are). Other countries such as France and India are also working on such systems. Those have generated much less alarm in the US than China has, although China's test system seems to be significantly more advanced. But China is already the US's primary strategic threat, so there are political reasons to talk up the dangers.

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There are two concerns. First is that China develops a nuclear deterrent on par with US and Russia. This traditionally means a second-strike capability that can guarantee that if a country with this capability were destroyed in a strategic exchange, the country who started it would share the same fate.

A second-strike capability (against ABM defenses) can be done simply by producing "ordinary" ICBM's, and launch platforms, in numbers large enough to overwhelm defenses. Given the balance of industrial capacity between US and China, and demonstrated ability to land things on the moon and mars etc, there it is a not a question of ability, but one of financial cost. With hypersonic weapons, it would be cheaper to get the same end result.

The second equally important concern, is that additional options open up by having a weapon type that can defeat ABM and air defenses singly, rather than by virtue of overwhelming numbers. This would make it possible to respond proportionally to possible US "kinetic" actions, that would be very inflammatory but short of total war, without limiting the possible responses to ones that are highly likely to produce full escalation.

To elaborate:

"Hypersonic weapons" referenced by this question are maneuverable, fly with lower trajectories, can hit targets with precision better than that required for strategic nukes, and most importantly, can avoid ABM and air defense systems individually, rather than relying on safety in numbers. All ICBM's are technically hypersonic in terms of speed alone, that by itself isn't sufficient.

From the point of view of China, the first use-case for this technology is to be able to respond to US making "limited" attacks on mainland China, such as a conventional attack on a key target like a port. The ability to make a proportional (non-escalatory) retaliatory strike on the continental US would take this threat off the table.

The second use-case for this technology, from the point of view of China, is to take out naval targets, as well as land bases for naval aviation, at extremely long range, covering much of, or even all of the Pacific Ocean. The context for the above is that it would increase the cost and risk of the US attempting a naval blockade of China.

The third use-case, from the point of view of China, is that it would make it possible to respond to the use of tactical nukes, again without having to escalate to a world-destroying MAD event.

It is believed in some quarters, typically by those who place a high value to unchallenged US "primacy" in use of force, that each of the above would "reduce the credibility" of the US position in international discussions.

We should also bear in mind that all of these scenarios are very unlikely. It is partly because of very generous budgeting, that there is an entire industry of planners and analysts and who work full time to write papers about the subject and publicize their findings, so it can generate unnecessary excitement.

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For the exact same reason that it cared about the missiles in Cuba during the 60's which was not enough time to react. Part of the problem with MAD is it requires the other side to be able to respond and there are ways to prevent that. It can be as simple as destroying the weapons first or preventing anyone with authority from ordering a counter strike.

https://www.britannica.com/event/Cuban-missile-crisis

Such missiles could hit much of the eastern United States within a few minutes if launched from Cuba.

As far as I am aware the president is the only person who can order a counter strike. If the first strike is designed in a way to take out a large portion of the chain of command before they can respond it could prevent a response at all.

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