Thomas J. Shattuck is the global order program manager at the University of Pennsylvania’s Perry World House, and a member of Foreign Policy for America’s NextGen Foreign Policy Initiative and the Pacific Forum’s Young Leaders Program.
In response to US House Speaker Nancy Pelosi’s early August 2022 visit to Taiwan, the People’s Republic of China (PRC) carried out an unprecedented military and economic response to punish Taipei. Much analysis has already covered the live-fire missile tests conducted around (and over) Taiwan, as well as the joint military exercises that accompanied them. (For further discussion of the latter, see “An Overview of Chinese Military Activity Near Taiwan in Early August 2022, Part 2: Aviation Activity, and Naval and Ground Force Exercises” by John Dotson, elsewhere in this issue.) Before these exercises, Beijing often expressed its displeasure about a Taiwan policy issue by sending military aircraft into Taiwan’s air defense identification zone (ADIZ). Starting in September 2020, in response to then-Under Secretary of State for Economic Growth, Energy, and the Environment Keith Krach’s visit to Taiwan, the People’s Liberation Army (PLA) began conducting regular sorties into Taiwan’s ADIZ. From September 2020 to July 2022, the focus of these incursions was the southwestern portion of the ADIZ, primarily between southern Taiwan and Taiwan-occupied Pratas/Dongsha Island (東沙島) in the South China Sea. Since Pelosi’s visit in early August, Beijing has initiated a new phase in its military pressure campaign against Taipei. This new phase has focused on near-daily Taiwan Strait centerline crossings, with less of an emphasis on the southwestern ADIZ area.
Since September 2020, Chinese military planes have only crossed the centerline of the Taiwan Strait on a few occasions. Both Beijing and Taipei have long tacitly observed and respected the demarcation of the strait, known as the Davis Line, after Air Force General Benjamin O. Davis Jr., who drew the line in 1955 after the signing of the Sino-American Mutual Defense Treaty in 1954.  It was drawn to reduce the risk of military confrontation between Beijing and Taipei, and particularly to reign in the Chiang Kai-shek (蔣介石) regime from drawing the United States into a war. From 1955 until 1999, no Chinese military aircraft crossed the centerline. While the line has never been an official, internationally recognized feature, both sides acknowledged and observed the norm for nearly 70 years. The centerline has existed longer than the so-called “1992 Consensus” (九二共識), the similarly ambiguous agreement that Beijing insists serves as the foundation for cross-Strait interactions.
As China’s military power began to increase vis-à-vis that of Taiwan (and even the United States), Beijing began to erode long-established norms, including respect for Taiwan’s ADIZ and the Davis Line. In 2020, the PLA conducted at least 380 sorties into the ADIZ, 22 of which crossed the centerline of the Taiwan Strait; followed by 972 sorties in the ADIZ in 2021, none of which crossed the centerline. In the months leading up to August 2022, 625 sorties were conducted, only one of which crossed the centerline. However, this changed significantly in August, when the PLA conducted 444 sorties, 323 of which crossed the centerline. Importantly, since August, Taiwan’s Ministry of National Defense (MND) has also begun to note whenever Chinese naval vessels entered these areas. This new phase of ADIZ activity—with the focus primarily within the Taiwan Strait—sets a dangerous precedent for Chinese military activity in one of the region’s (and the world’s) most important and active waterways.
What’s Crossed the Taiwan Strait Centerline?
One of the most important aspects of the centerline crossings is the model of aircraft that are used for these types of incursions, as opposed to the “regular” southwestern ADIZ incursions. Nearly every single sortie crossing the centerline has been made by fighter aircraft: J-10, J-11, J-16, JH-7, and SU-30. Of particular importance is the exponential increase in the use of the SU-30 in August 2022.
Before Pelosi visited Taiwan, the SU-30 flew only 48 sorties into the ADIZ, none of which crossed the centerline. The month with the highest frequency of use was October 2021, with 20 sorties. In August 2022, however, SU-30 fighters flew 176 sorties across the centerline. During that month, the SU-30 has served as the fighter aircraft of choice for these centerline crossings: the J-10 has flown 22 sorties, the J-11 77 sorties, the J-16 36 sorties, and the JH-7 seven sorties. The SU-30 has flown more sorties than all of those aircraft combined, with the focus of its use occurring during the live-fire joint exercises in early August. On August 3, 16 SU-30s crossed the centerline; followed by 12 on August 4; 24 on August 5; and 10 on August 6. On August 18, another 12 made a crossing.
The fact that Beijing almost exclusively reserves the Taiwan Strait for fighter aircraft is not particularly surprising, since their use sends a clear message: the Taiwan Strait crossings and exercises are not meant to be intelligence-gathering missions, but are instead practice for offensive contingencies like a blockade or invasion. The Chinese military will need to achieve air superiority over the Taiwan Strait to launch a successful invasion of Taiwan proper, so sending these fighter aircraft serves as preparation for that goal. If anti-submarine aircraft like the Y-8 ASW variant or electronic warfare aircraft like the Y-8 EW variant were the predominantly used aircraft in the Strait, then Beijing would be sending a less aggressive message. These two other categories of aircraft are the second and third most used in ADIZ incursions, but they are primarily used in the southwestern region. Beijing wants its Taiwan Strait crossings to send as clear a message as possible: the waterway is the shortest distance and most direct route from the People’s Republic to Taiwan.
The true danger lies in the normalization of centerline crossings as Beijing seeks to increase its military pressure on Taiwan in a post-Pelosi visit environment. If the international community reacts minimally to this new development—as has occurred since September 2020, when Beijing began its regular ADIZ incursions—then centerline crossings will become another new element of the now-diminished cross-Strait status quo. Additionally, these activities could provide Beijing with cover should the day come that an invasion does occur, as a “normal” exercise featuring several squadrons of aircraft crossing the centerline of the Taiwan Strait could quickly transition into something far more aggressive. While this situation is not likely to occur in the near-term, the likely next step in Taiwan Strait centerline crossings will be increasingly deeper penetration closer and closer to Taiwan, potentially escalating to incursions into Taiwan’s actual territorial airspace.
Implications for the Future
As Taiwan seeks to expand its international space and unofficial ties with other countries, Beijing will continue to react by crossing the centerline of the Taiwan Strait, among other responses. Since Speaker Pelosi refused to back down and made the trip to Taipei despite strong protests by Chinese officials, Beijing has seemed determined to ensure that Taiwan regrets these efforts by foreign dignitaries to signal public support for Taiwan. The more that this red line is crossed by high-profile individuals, the stronger the reaction from Beijing will likely be. The post-Pelosi exercises have demonstrated that China is not afraid of conducting unprecedented exercises around Taiwan and changing the cross-Strait status quo. Before August 2022, near-daily Taiwan Strait crossings seemed like a bridge too far for Beijing, since they had been so rare for so long. After Pelosi’s visit, however, Taiwan Strait centerline crossings are now a new facet of the cross-Strait status quo. The unprecedented quickly gets folded into the norm. Ultimately, this is one of the most dangerous elements of Beijing’s Taiwan strategy: desensitization to military coercion. Should the world accept this new mode of PLA aviation activity, it would allow Beijing to continue to frame the security responses to US regional policy and Taiwan’s international affairs.
Beijing’s salami-slicing tactics will continue to slowly squeeze Taiwan across a number of spheres, to include straining the resources of Taiwan’s military. In March 2021, Taipei announced that it had ceased intercepting every single ADIZ incursion. Taiwan’s military would still track the aircraft with surface-to-air missile systems and issue warnings to leave the area, but it would only intercept Chinese aircraft on an as-needed basis. This decision was driven primarily by economic restraints, as the fuel costs for intercepting each incursion were having a negative effect on the defense budget. By changing the nature of the incursions from the distant southwestern area to the Taiwan Strait, Beijing can attempt to force Taiwan to now revert back to its old policy and intercept every single Taiwan Strait crossing.
Given the significant number of incursions in August 2022 alone, Taiwan’s military will not be able to afford to intercept every single aircraft that crosses the centerline. China simply has more aircraft than Taiwan, as well as a huge budgetary advantage. The initial ADIZ incursions did not break the Taiwanese military budget, but the military had to divert funds to the interceptions from other important needs. With this new phase of near-daily Taiwan Strait incursions, Taiwan’s military will have to make difficult choices about what to do and when to intercept. Tracking aircraft in the southwestern ADIZ was a wise policy choice given the constraints of Taiwan’s military, but flights across the centerline will be a harder decision given how much closer these aircraft are to Taipei.
Looking to the future, considering that “phase one” of ADIZ incursions lasted for nearly two years, we can expect that “phase two” of Taiwan Strait centerline crossings will last for some time in their current form—before Beijing eventually decides to change the terms of engagement again, and escalates into a potential “phase three.” A new phase of ADIZ escalation would likely include flights that go closer to Taiwan’s territorial airspace. Instead of breaching the centerline of the Taiwan Strait slightly and then turning around, Chinese military aircraft could potentially continue toward Taiwan and turn around just before hitting that point, which would undoubtedly result in Taiwanese aircraft attempting to intercept them. Beijing will likely wait for another future moment in time when the United States and Taiwan move closer together, or seemingly cross one of the PRC’s red lines, before it decides to initiate a new phase in this response toolkit. Such a move would allow Beijing to play the victim and claim that it was forced to increase military pressure on Taiwan. This tactic has historically been the case whenever Beijing decided to further squeeze Taiwan, and it will likely continue that way into the future.
The main point: Since US House Speaker Nancy Pelosi visited Taiwan in early August 2022, Beijing has sent nearly 300 military aircraft across the centerline of the Taiwan Strait, breaking a nearly 70-year understanding. Following two years of near-daily incursions into Taiwan’s southwestern ADIZ, the post-Pelosi focus on Taiwan Strait centerline incursions marks a new phase in Chinese military coercion of Taiwan, a pattern likely to continue indefinitely.
 The line runs 26°30′ north latitude, 121°23′ east longitude to 24°50′ north latitude, 119°59′ east longitude, to 23°17′ north latitude, 117°51′ east longitude.