Much of what I have written about Taiwan defense issues assumes that the primary challenge facing Taiwanese forces and their allies is defeating (and thus deterring) a proper amphibious invasion. Two recent reports argue—convincingly, I think—that this assumption is wrong.
If ordered to compel reunification by military force, the PLA would bring every tool to bear. Among its most effective lines of operations would be a long-term air, maritime, and information blockade of Taiwan. Such a blockade could be the main effort, eschewing an attempted landing altogether, or it could be part of a larger invasion campaign. Most importantly, even if the landing failed, the PLA could continue the blockade indefinitely and neither US nor Taiwan forces would have much ability to overcome it.
The Communist Party (CCP) leadership could not afford to accept defeat. The passions aroused by the war itself and by the propaganda effort in support of the war would not allow the Party to stop short of a political outcome they could credibly sell as a victory. If such a formula were available in the immediate wake of a failed landing, they might be tempted to take it. If not, they would have no choice but to continue the conflict by whatever means remained.
Even at this point in the conflict, after weeks or months of intense fighting, the loss of much of its landing force, expenditure of its ballistic missile inventory, and very severe attrition of its navy and air force, the PLA could still have the upper hand in enforcing the blockade. The distinctive geography of the Taiwan theater would finally start working in the PLA’s favor and its remaining short-range strike assets would still be useful.
...In my assessment, China could continue the blockade operation indefinitely even with the severely diminished force that remained after a failed landing and months of air and naval attrition. US forces could probably push through a trickle of relief supplies, but not much more. 
Henley is disturbed by how little we know about how this scenario will play out:
Unlike Taiwan’s will to resist, its ability to resist a long-term blockade is something we should know much more about than we do. I am aware of no study in the United States or Taiwan examining Taiwan’s wartime consumption rate of critical materials, its peacetime stockpiles, or which stockpiles would likely be lost to PLA fires. There is no assessment of what must get through a blockade to keep Taiwan alive, what types of materiel in what quantities, or what Taiwan’s domestic production of food, water, supplies, and equipment might be under wartime conditions. And to the best of my knowledge, no one has considered in detail how to get enough materiel through a PLA air and maritime blockade, day after day, week after week, while working to break down the blockade itself.
I am aware of one such study from 2013 that attempts to assess Taiwanese stocks of oil and jet fuel. It concludes:
Taiwan’s total stockpile from government and commercial sources could provide 732 days, or about two years, of civilian consumption. Such an amount is beyond adequate for a plausible emergency scenario, assuming there is no active military component. Factoring in military demand, however, causes the days of available supply to drop precipitously. In an air war such as the one modeled above, Taiwan could supply 100 percent of military needs and 100 percent of civilian needs for 152 days, or about five months—still a solid emergency cushion, though a much smaller one.Now that study is seven years old. I do not know how accurate it is now. Moreover, it assumes that the Taiwanese do not lose any fuel to PLAF or PLARF attacks, a wildly implausible operating assumption. But it does present a rosier picture of Taiwanese preparedness than Henley seems to fear.
It would not surprise me if nestled away in Taiwanese military journals are a few more studies of this type, but I am not aware of them. In English there is nothing else to draw on. What we have is not enough. Henley argues that given how little this has been studied, security analysts' confidence that the Chinese will not resort to blockade, and that if Chinese did so resort their blockade would not succeed, is unfounded.
It is hard to argue with this logic.
Henley's blockade worries give him an unorthodox take on the true "center of gravity" of a cross straits conflict. Current Taiwanese defense planning sees the center of gravity on the landing beach, and their strategy is built around destroying the PLA landing force before it can dig in there. Americans, perhaps influenced by the traditional naval leadership of INDOPACOM, instead tend to see victory in terms of the number of PLAN vessels sunk. Talk cross straits contingencies with enough American military officers and you will see this pattern. Their optimism or pessimism usually rests on their personal assessment of America's submarine forces and Chinese ASW capabilities. Those confident that American attack submarines can pierce the Chinese anti-access bubble are bearish on the PLAN successfully getting a proper invasion force across the strait. Those who think the Chinese can keep American submarines at bay are far more pessimistic.
Henley focuses on a different domain altogether:
The center of gravity for this entire conflict, in my judgment, is the PLA air defense network. Over many years of participating in Taiwan Strait war games and tabletop exercises, I observe that Taiwan’s air defenses are almost always disabled within the first few days of the conflict, but China’s integrated air defense system (IADS) along the Taiwan Strait remains effective for as far into the conflict as the exercise examines. This in turn limits the United States to long-range stand-off weapons or precision-strike incursions by stealth platforms. I assume I am not the only person to have observed this and that US forces are working on the issue.
Success in this area would have the greatest impact on the overall conflict, more even than finding a way to defend US air bases from Chinese missile strikes. Poorly defended bases will still generate some combat sorties, particularly as the conflict drags on and the Chinese expend their inventory of theater-range missiles. But a functioning air defense network greatly reduces the impact those sorties can have. Conversely, defeating the Chinese IADS would open the door to the kind of air campaign that has proven decisive against less capable opponents. More specifically, enabling US air operations over the Strait would be our best hope for getting cargo into Taiwan’s western ports. The PLA’s short-range anti-ship assets can be extremely effective under a tight air defense umbrella, but much less so in the glare of US air power. The PLA air blockade, meanwhile, simply ceases to exist without the IADS. 
If Henley is right and the Chinese IADS are the critical node in the Chinese war effort, this has important strategic and diplomatic consequences. Most important is this: the core of the Chinese IADS are mobile surface to air missile systems (like the Russian bought S400, S300, and the indigenous HQ-9) and the mobile radar systems that support them. These forces—which the Pentagon admits outclass their American counterparts—are ground based.- The PLAN's destroyers and the PLARF's small fleet of airborne early warning and control ("AEWAC") planes are also a part of this system, but they play the smaller part. Any fight to destroy the Chinese IADS is a fight to destroy ground based missile launchers—missile launchers that will be located on mainland Chinese soil.
These ground based systems will not be destroyed quickly. As one helpful review of the Chinese IADS system concludes that, while "completely rolling back an IADS the size, depth and complexity of those of Russia or China" is possible, it "would most likely take weeks and possibly months of full-scale warfighting."
Part of the appeal of the "destroy the invasion fleet" strategy is precisely that it avoids months of full-time warfighting, especially months of attacks on mainland targets. Those who want to avoid escalation eagerly search for ways to keep the fight "in theater." But with surface to air missiles being fired from mainland locations hundreds of kilometers inland, the distinction between military platforms "in theater" and on the mainland grows blurry.So there are real stakes then to this debate. It is interesting to see how much of this debate turns on essentially political questions. Just how willing is Beijing to accept the costs of a multi-month blockade after having lost much of its Navy or an invasion force? Henley thinks they will be willing to keep plugging away, confident that if nothing else they can outlast the Taiwanese:
Most of the operational approaches available to US forces would not serve to end the war. Defeating the landing operation is feasible given a large enough US effort, but to repeat my earlier point, that would merely move the war into the next very extended phase. It would not end the military conflict, nor would it necessarily go very far toward creating the conditions for a political settlement...
The problem is that Chinese leaders certainly would think far more than twice before going to war against the United States. The military cost is only one of myriad reasons not to do it, and not the most important reason by far. If they decide they must do so anyway, they will have made that decision in full acceptance that the war will be economically devastating to China for decades to come and that its failure would severely endanger the Communist Party’s hold on power. At that point, the “cost imposition” dial is at 11; it won’t go any higher.
This brings us back to my central point: if we can’t defeat the blockade, we can’t prevail.
I would not be so confident. One of the odd things about American strategic culture is the cataclysmic nature of our strategic thinking. We jump immediately to total ends: for two centuries we have equated "war termination" with total surrender. But this is not the historical norm. It certainly is not a marked feature of Chinese military history. I can imagine many scenarios where the Chinese conclude that, after having destroyed the ROC Navy and Air Force, killed Taiwan's leaders, reduced her communications bases, air defense system, and radar stations to rubble, and inflected incalculable suffering on the Taiwanese people, they have successfully "taught a lesson" to the Taiwanese and seek a termination of hostilities in exchange for a return to the status quo (knowing full well they will recover from their losses far faster than the Taiwanese can hope to).
I can also imagine a scenario of rising discontent at home. It is it so fanciful to picture a Chinese people dispirited by battlefield defeats or afraid of escalating destruction as the Americans and Japanese get involved in a war they assumed would be full of quick and easy victories? Behind this scenario is the recognition that all costs are marginal costs. In the face of domestic discontent marginal domestic costs of continuing operations—especially operations like a blockade, which don't offer any morale-boosting headlines—may exceed the marginal costs of admitting defeat.
This sounds more plausible when we consider the types of costs such a war will impose on the Chinese people by default. A recent report by Robert Blackwill and Philip Zelikow reminds us of these costs:
In this context, it is useful to recall and review what happens when the United States goes to war with a country, even a small war. First, the United States would freeze all assets owned by that country, or its citizens, in the United States. In this case, the United States could have to recognize an independent Taiwanese government, even in extremis a government-in-exile of some kind, in order to distinguish and protect Taiwanese-owned assets from being seized and possibly forfeited along with all Chinese-owned assets.
Second, the United States would cut off, and strictly control, any business transactions or dollar transactions with China. No trading with the enemy would be conducted. This would necessarily end any payment of interest on American securities, government or private, held by Chinese citizens or the Chinese government. It would include at least the suspension of interest payments on Treasury bonds held by the Chinese government or Chinese citizens.And all of that is without cyber-attacks, blockades, and other measures less automatic than the ones that Blackwill and Zelikow describe. Of course, Henley is right: if Beijing opts for war that means it opts for war with full knowledge all of this may happen. But if the Party leadership (or just as importantly, the Chinese people) go to war with the belief that victory will be a quick and easy thing, their tolerance for bearing these costs over an extended period of time might be much smaller than Henley predicts.
These are profound measures. They would affect trillions of dollars of assets in the United States and around the world. We presume that China would retaliate in kind. These moves would immediately trigger a large and devastating financial and economic crisis (as also happened immediately after the outbreak of war in August 1914, because of the asset controls and commercial closures, not because of the impact of the military operations themselves.
These effects would be so great that it is not credible to threaten them as sanctions. We are not proposing a strategy of coercive diplomacy. This is a strategy to spell out how world politics and the world economy are likely to fracture after such a terrible break. That is why robust U.S. and allied local military capability is so essential. Without the impetus of an outbreak of fighting, Washington’s deterrence threat of such gigantic measures could seem hollow.However, if a violent local conflict does occur, such extraordinary measures would not only be adopted but also likely implemented practically overnight. If Japanese citizens had also been killed, and Japan was embroiled in the local war, then Japan would probably adopt a similar set of draconian measures.
Given their sensitivity to the costs of full campaigning, Blackwill and Zelikow suggest another measure short of armed invasion that the PLA may opt for. They call it a "quarantine":
By quarantine, we do not mean blockade. In a quarantine scenario, the Chinese government would effectively take control of the air and sea borders of Taiwan. It would declare control over Taiwan’s airspace so that, in effect, Taipei’s Taoyuan International Airport was no longer its own international gateway, and Kaohsiung was no longer its own international port. The Chinese government would run effectively a clearance operation offshore or in the air to screen incoming ships and aircraft. The screeners could then wave along what they regarded as innocent traffic. Or they could request that suspect ships or aircraft divert for full Chinese customs clearance at a neighboring airport on the mainland or in a neighboring port, such as Fuzhou or Guangzhou, or Xiamen or Shantou. China has excellent “domain awareness,” having plenty of ships from its navy, coast guard, and maritime militia at its disposal to accomplish this task....
The Chinese government could run such a quarantine without actually trying to take effective control of the Taiwanese people themselves. In this scenario, the Chinese government would allow the people in Taiwan to run their own affairs on the island, at least for some time, as China showed that it controlled who came (and perhaps who went).
This scenario includes variations, in which China engages Taiwan’s air and naval forces that contest this quarantine, or fires salvoes of missiles into Taiwan to intimidate its citizens into compliance. The point is that, in all of these scenarios, China neither invades Taiwan nor attempts to cut off supplies of food or energy, as it would in a full siege. The goal is to force Taiwan to accept a loss of control, cutting Taiwan off from, at least, transfers of military equipment and associated foreign experts. This scenario places a heavy burden on foreigners to decide whether they will deliberately choose to make a military challenge to this assertion of Chinese sovereignty. In this context, with the Chinese making these arguments, the outsider, such as the United States or Japan, would first have to negotiate the divided and contentious domestic politics surrounding such a deliberate and dangerous military challenge. At the same time, all would be watching the behavior of Taiwan’s citizens and their political divisions and quarrels about how to proceed....
This scenario could then seem to offer the prospect, to a Chinese planner, of relatively manageable risks and high rewards. China would not only demonstrate meaningful sovereignty; it would gain the military benefit of effectively blocking the further military modernization of Taiwan’s defenses, possibly permanently. If that were successful, the longer-term effects on Taiwan’s domestic politics could be imagined.
I find this scenario particularly disturbing: I do not think the United States and Japan currently have any easy proportional counter-response to employ against a "quarantine." While Japanese defense officials have recently sent some very strong signals about the importance of Taiwan to Japan's national defense, they have not communicated this effectively to the Japanese public. Moreover, American and Japanese officials have not done joint contingency planning for nor gamed out responses to this sort of Taiwan challenge. It will be difficult to do so on the fly, with the American and Japanese publics unenthusiastic about Taiwanese liberties and significant business interests in both countries resolutely opposed to actions that might threaten their China-buoyed bottom lines.
Something similar could be said for Chinese attacks on Taiwan's outer islands. In all cases, we will be in a far better position to respond to Chinese aggression if Taiwanese, Japanese, and American officials have been coordinating, contingency planning, and vigorously preparing public opinion for a robust response well before the crisis arrives. The time to think through these problems is now.
 Lonnie Henley, "PLA Operational Concepts and Centers of Gravity in a Taiwan Conflict," Testimony before the U.S.-China Economic and Security Review Commission (18 February 2021), 4.
 ibid., 6.
 Rosemary Kelanic, "Oil Security and Conventional War: Lessons From a China-Taiwan Air Scenario," Council on Foreign Relations report (October 2013), 8.
 The best English language overview of the current Taiwan defense concept is Lee Hsi-min and Eric Lee, "Taiwan's Overall Defense Concept, Explained," The Diplomat (3 November 2020). For examples of American views see Michelle Flournoy's comments in Foreign Affairs last year:
if the US military had the capability to credibly threaten to sink all of China's military vessels, submarines, and merchant ships in the South China Sea within 72 hours, Chinese leaders might think twice before, say, launching a blockade or invasion of Taiwan; they would have to wonder whether it was worth putting their entire fleet at risk.Robert Work said something similar a year before:
Pentagon leaders should challenge the armed services to solve very hard, very specific problems, Work said: Sink 350 Chinese navy and coast guard vessels in the first 72 hours of a war.Blackwill and Zenilow, cited below, cite both of these examples on p. 37 as senior defense officials seeing a "need to develop a capability to destroy every Chinese vessel in the South China Sea within seventy-two hours." I credit them for drawing my attention to the parallels between both statements, but am somewhat mystified at their reference to the South China Sea, when both Work and Flournoy are discussing Taiwan contingencies. For the original statements see Michèle A. Flournoy, “How to Prevent a War in Asia,” Foreign Affairs (18 June 2020) and Sydney Freedberg Jr., “US ‘Gets Its Ass Handed to It’ In Wargames: Here’s a $24 Billion Fix,” Breaking Defense (7 March 2019).
 This is also the argument you will hear from the defenders of Taiwan's indigenous submarine program (see for example Mark Stokes comments here), and I agree with these folks in the abstract. But the subs cost a lot and will be slow in coming. Too slow, perhaps, to make a difference.
 Henley, "PLA Operatioal Concepts," 6.
 For that judgement see Military and Security Developments Involving the People's Republic of China: 2020 (Washington DC: Office of the Secretary of Defense, 2020), vii.
 Justin Bronk, "Modern Russian and Chinese Integrated Air Defence Systems: The Nature of the Threat, Growth Trajectory and Western Options," RUSI Occasional paper (January 2020), 32.
 Robert Blackwill and Philip Zelikow, The United States, China, and Taiwan: A Strategy to Prevent War (Washington DC: Council on Foreign Relations, 2021), 45-46.
 ibid., 35-37.