Taiwan is unlikely to thwart Chinese military air superiority in a cross-strait conflict, while tactics such as China's use of civilian ships for military purposes have eroded U.S. spy agencies' ability to detect a pending invasion, according to leaked Pentagon assessments that contain troubling details about the self-governed island's ability to fend off war.

The assessments state that Taiwan officials doubt their air defenses can "accurately detect missile launches," that barely more than half of Taiwan's aircraft are fully mission capable and that moving the jets to shelters would take at least a week - a huge problem if China launched missiles before Taiwan had a chance to disperse those planes.

The classified documents addressing a potential conflict suggest China's air force would have a much better shot at establishing early control of the skies - a strategy that Taipei itself believes will underpin an attack - than Russia did in Ukraine.

The document leak, which first came to authorities' attention last week, has provided extensive insight into U.S. intelligence activities worldwide. Many of the several hundred assessments that have surfaced thus far date to February and March; they first appeared on the Discord messaging platform before spreading elsewhere online. Both the Pentagon, where many of the materials appear to have originated this year, and the Justice Department are investigating the security breach.

The FBI arrested its primary suspect, 21-year-old member of the Massachusetts Air National Guard Jack Teixeira, on Thursday afternoon.

The revelations about Taiwan's readiness come as U.S.-China relations are at their lowest point in decades and concerns continue to grow about a potential conflict between Taipei and the People's Liberation Army, China's fast-modernizing military that is roughly 14 times the size of its neighbor's force.

One assessment notes that the PLA's modernization, its heightened operations tempo and the use of civilian ferries in exercises in the Eastern Theater Command near Taiwan are "eroding" the U.S. intelligence community's ability to detect abnormal activity and preparations for "an attack on Taiwan."

Another assessment takes aim at Taiwan's military and civilian preparedness. It says the island's current doctrine of firing two air defense missiles per target "would be strained under high-volume PLA fires" from China's short-range ballistic missile system, dispersed across multiple moving launch platforms. Taiwanese airmen train for shooting at single unmoving targets.

Moreover, Pentagon analysts note, Taiwan's missile warning drills are highly scripted and inadequate for steeling civil authorities and the public for "a real-world event."

Though far from a comprehensive analysis of China's capabilities and Taiwan's vulnerabilities, the documents collectively paint a grimmer picture of Taiwan's overall readiness. They also serve as a warning to policymakers that China's aggression is becoming more intense even as its intentions become less predictable.

A spokesperson for the Office of the Joint Chiefs of Staff declined to comment. Taiwan's Defense Ministry said in a statement that it "respects outside opinions about its military preparedness" and that its defense systems are "carefully constructed based on enemy threats." The ministry added: Taiwan's response to recent Chinese military exercises showed that officers are "absolutely capable, determined and confident" in ensuring security.

CIA Director William J. Burns has said Chinese President Xi Jinping has directed that his military be capable of seizing Taiwan by the PLA's centennial in 2027. But that doesn't necessarily mean he will deploy troops then or at any other time, Burns hastened to add, saying he believes Xi and his military leadership have doubts about whether an invasion would be successful. The Russians' experience in Ukraine has "probably reinforced some of those doubts as well," Burns told CBS' "Face the Nation" in February.

Gen. Mark A. Milley, chairman of the Joint Chiefs of Staff, said in November that the Pentagon is working to make sure that Taipei can defend itself and that the U.S. military is prepared should the island be invaded.

Milley pointed out that the Chinese military hasn't seen combat since the 1970s and would be playing a "very, very dangerous game" if it attacks Taiwan. Subduing the 23 million people there and negotiating mountainous terrain would be extremely difficult, he said, and drew parallels to the Russian invasion of Ukraine - an ongoing conflict that has left hundreds of thousands of soldiers and civilians dead or wounded.

Indeed, China's ability to mount an amphibious attack would be hampered by limited options for delivering gasoline to its fuel-hungry landing brigade, according to one of the leaked documents. That would make it difficult to sustain a foothold on Taiwan, creating an opportunity for the United States and Taiwan to thwart an invasion at an early stage, the assessment noted.

Securing the Port of Taipei would be China's best refueling option, it said. But both sides would face challenges: The PLA has not practiced seizure operations. Taiwan has no plans for sabotaging such an attempt.

One Chinese official familiar with PLA aims in the Eastern Theater told The Washington Post recently that the country "has the ability to swiftly defeat Taiwan in the air and sea - that is not in question." But, the official continued, "the United States shows every day that it is willing to meddle in Chinese affairs. We need to prepare for the scenario [of U.S. intervention on Taiwan's behalf], and that is clear in the operations being conducted now."

The official called recent drills near Taiwan "simply a deterrent" and important to improving morale and "mental readiness" - particularly of pilots. "Our military is developing quickly, and the technology is advancing quickly," the official said. "This creates problems ensuring [pilots] have appropriate experience. So there needs to be practical training."

Yet as difficult as an assault on Taiwan would be for China, Pentagon intelligence analysts have detected a number of deficits in Taipei's planning.

One concern is that officials might withhold air defense systems early in a conflict to save them for later. Independent analysts consider such a delay problematic since China has almost 40 air bases within striking range of Taiwan. Thomas Shugart, an adjunct senior fellow at the Center for a New American Security, said many of those bases have hardened shelters to limit damage from weapons and many of the shelters are covered to make it difficult for satellites to detect where aircraft are parked. The PLA has built more than 800 covered air shelters within 600 miles of Taiwan over the last decade, Shugart noted.

The assessments prepared by the Pentagon's Joint Staff intelligence directorate state that Taiwan's air defense units lack a "common operating picture," meaning an ability to see where all units are at a given time. They also lack compatible secure radios. Targets are not deconflicted, raising the risk of multiple units firing on the same target.

In an oblique criticism, one document says Taiwan's air defense commanders "may hesitate to engage manned aircraft due to fear of escalation, even with first strike orders or imminent air threats.''

"We can't fire the first shot," explained Chang Yan-ting, a retired Taiwan Air Force deputy commander. "We are not allowed to throw a punch until we get hit. In any emergency, we are bound hand and foot because we set advanced limits on ourselves about when to respond."

Taiwan's expansion of Air Force conscription in 2024, part of broad combat readiness reforms that extended compulsory military service to one year from four months, is "unlikely to significantly improve" its air defense effectiveness without addressing several issues, according to the leaked documents.

While air superiority is critical for a successful invasion of Taiwan, it alone will not win a war, said Matt Pottinger, a deputy national security adviser under President Donald Trump. Still, he said, Taiwan's shortcomings in air defenses require urgent steps by its leaders, the United States and Japan to ramp up capabilities to repel Chinese aircraft and missile-launchers. Pottinger, like other experts interviewed for this story, was speaking generally and had not seen the leaked documents.

China's intensifying military activity around Taiwan is undermining the intelligence community's ability to accurately track what is normal and what is escalatory, raising the risk of accidents and miscalculation, the assessments warn. Beijing has carried out "large-scale military exercises simulating amphibious assaults, blockades, air raids and joint fire power strikes" twice within the last eight months, most notably after the visit of then-House Speaker Nancy Pelosi (D-Calif.) to Taiwan in August, when it launched ballistic missiles over the island and sent dozens of jets across the unofficial sea border between the two jurisdictions.

The most recent activity - following this month's meeting between Taiwan President Tsai Ing-wen and House Speaker Kevin McCarthy (R-Calif.) in California - wasn't as bellicose. Should future exercises get significantly larger, that would make judgments about China's intentions more difficult, said Joel Wuthnow, a senior research fellow at National Defense University.

"You need to have a fairly high level of confidence that you're facing use of force and also time to make critical political decisions if you're the United States," Wuthnow said. "If you have ambiguities or doubts as well as a compressed timeline, it could potentially complicate your ability to mobilize your own forces, which is a huge challenge, because the United States needs to mobilize across the huge expanse of the Pacific Ocean. Reduced warning could make it difficult to get there on time."

Distance is a significant complicating factor in a defense-of-Taiwan scenario, experts agree.

"We cannot get there quickly," said Oriana Skylar Mastro, a fellow at Stanford University's Freeman Spogli Institute for International Studies and at the American Enterprise Institute. "It's basically submarines and U.S. aircraft that are going to be operating from the southwest islands of Japan and eventually from bases in the northern Philippines. If China takes out those bases, the United States doesn't have a lot of options."

Unlike Ukraine, "there is no situation under which Taiwan can defend itself without direct military intervention from the United States," Mastro said. "Taiwan has to be able to hold out long enough for the United States to get enough forces in theater."

Behind the scenes, the U.S. government has pushed Taiwan to bolster its defenses - particularly with nonconventional arms such as anti-ship missiles and other advanced weaponry that are more likely to survive a Chinese attack. In response, Taipei is buying U.S.-made Harpoon anti-ship missiles, Stinger antiaircraft missiles and High Mobility Artillery Rocket Systems (HIMARS).

In the event of a conflict, however, one assessment expects that China will "very likely" use its space capabilities to disable U.S. satellites in an effort to deprive the United States of useful intelligence. It also may rely on satellites for long-range strikes on U.S. ships, subs and jets spread across the vast Pacific, the document states.

If China were able to successfully disable the U.S. satellites, "it would make any effort to support Taiwan bloodier," said Dean Cheng, a nonresident senior fellow with the Potomac Institute for Policy Studies. "More ships would be sunk. More pilots would be lost. More bombs would go off target. Our forces would not be able to coordinate nearly as well."

The assessment underscores the wide array of Chinese space weaponry, such as roving antisatellite missile launchers and lasers, that could by used to "deter, disrupt, delay, and, if necessary, defeat" a U.S. intervention to aid Taiwan. The bottom line, according to the document, is that China considers such capabilities "critical for deterring the U.S. from entering a conflict, impairing the U.S. if deterrence fails, and enabling its own war-fighting capabilities."

The Washington Post's Dan Lamothe in Washington and Vic Chiang in Taipei contributed to this report.