Ever since China set up its first air defense identification zone (ADIZ) in the East China Sea in November 2013, a Chinese ADIZ has hung as a sword of Damocles over the South China Sea. The same day as China’s Ministry of Defense announced the establishment of the East China Sea ADIZ, the ministry’s spokesman proclaimed, “China will establish other air defense identification zones at an appropriate time after completing preparations.” Since then, official statements by both China’s Ministry of National Defense and Ministry of Foreign Affairs have never ruled out the possibility of a South China Sea ADIZ, saying consistently that setting up such an ADIZ is the right of China as a sovereign state. Adding to this suggestion, sources close to the Chinese military occasionally told foreign journalists that China had plans and was ready to impose an ADIZ in the South China Sea. In early 2016, Navy Senior Colonel Liang Fang, a renowned strategist in the National Defense University, publicly urged the People’s Liberation Army (PLA) to declare an ADIZ in the South China Sea. All these announcements might be deliberate efforts to bluff China’s rivals, but the possibility of a Chinese ADIZ in the South China Sea in real.

Will China set up a South China Sea ADIZ? If it does, when will it do so, and with what size and scope? These questions have been raised numerous times since November 2013. A South China Sea ADIZ was again a hot issue following a remark by China’s Vice Foreign Minister in relation to the Permanent Court of Arbitration’s South China Sea ruling. How do you predict what the South China Sea ADIZ? This article will help both readers who want to make informed judgments about others’ predictions and readers who want to make informed predictions themselves to think systematically about the subject.

Will China Set Up an ADIZ in the South China Sea?

The South China Sea ADIZ is a dog that hasn’t barked, but it can turn out to be one of three animals.

First, it can be a dog that will eventually bark. Most observers believe that China’s declaration of an ADIZ in the South China Sea is just a matter of time. Two reasons are paramount to support this belief. First, China’s official statements suggest that it already has plans for the South China Sea ADIZ that are to be executed when time is ripe.

Second, the facilities that China is building on the disputed islands in the South China Sea are too large for the need of the local communities. Some of these facilities include four three thousand-meter-long runways on Woody Island, Fiery Cross Reef, Subi Reef and Mischief Reef and a high-frequency radar station on Cuarteron Reef. China has also deployed to Woody Island long-range surface-to-air missiles that can reach two-hundred kilometers. In the eyes of many experts, the most logical application of these infrastructure and weapons systems is to support an ADIZ in the future.

But the South China Sea ADIZ can also be a dog that never barks. Even if China already has a plan to set it up, the time may never be ripe for a formal declaration. At least four arguments can be brought up to support this possibility.

First, “China may have learned from its East China Sea ADIZ that this particular game is not worth the candle.” As David Welch explains, “Declaring a South China Sea ADIZ would seriously undermine Chinese interests, aviation safety and international confidence in Beijing’s judgment. Very likely it would prompt other claimant states to declare overlapping ADIZs of their own.” However, some other experts doubt whether China has really learnt the lessons of the East China Sea ADIZ this way. In retrospect to China’s East China Sea ADIZ, Zhu Feng argues that the benefits it brings have outweighed the risks.

Second, an ADIZ may undermine the ambiguous nature of China’s claims in the South China Sea. Ambiguity has arguably served China’s interests well, so China will have to think twice before it imposes an ADIZ in the South China Sea.

Third, some of China’s rivals are holding cards that can deter China from declaring an ADIZ in the South China Sea. Most effective among these cards is likely a Vietnamese ADIZ over the Paracel Islands, which can reestablish some forms of Vietnamese administration over the islands. China may also be deterred by the prospects of Vietnam launching a legal action against it, or Vietnam and the Philippines granting the U.S. military regular access to strategic places on the South China Sea coast such as Cam Ranh Bay and Da Nang in Vietnam or Ulugan Bay, Subic Bay and Zambales Province in the Philippines.

Fourth, China can leverage its hypothetical ADIZ in the South China Sea as a deterrent to possible challenges from the other users of the sea. If an ADIZ works best when it is unborn, it will be kept unborn.

Finally, the South China Sea ADIZ can be a dog that barks under the guise of a different animal. This camouflage may take various forms. China may impose one or more exclusion zones not under the name of ADIZ.

Alternatively, it may be a quasi or de facto ADIZ that is undeclared but nevertheless actively enforced. According to the Philippine judge Antonio Carpio, China is already effectively enforcing a quasi-ADIZ in the South China Sea by warning Philippine planes flying over the Spratlys via radio to “stay away from the area.” Similar warnings have been sent to military and civilian flights from other countries, including the United States and Australia. Currently, China’s quasi-ADIZ appears to cover no more than twenty nautical miles from the shores of some Chinese-controlled features.

Why Does China Need an ADIZ?

The question whether China will set up a South China Sea ADIZ can only be answered adequately if one understands why China needs an ADIZ in this area. Alas, the utility of an ADIZ is one of the least discussed topics in the discourse about China’s ADIZ. There is a general tendency to simply assume that China’s ADIZ is what its name implies—an air defense zone or a military tool of territorial control. But the utility of an ADIZ goes beyond the military realm and an ADIZ does not need to be effectively enforced in order to bring benefits to the country that declares it. As with other policy tools, it can perform political, diplomatic and legal functions.

An ADIZ can perform one or more of at least six functions. Two of these functions (early warning mechanism and exclusion zone) require effective enforcement, while three other (sovereignty marker, bargaining chip and signaling device) rely more on a formal declaration. One of the functions (deterrent) can only work without a declaration of the related ADIZ.

-ADIZ as an early warning mechanism. This is the original use with which the United States created the first ADIZs during the Cold War. It did so to reduce the risk of a surprise aerial attack from the Soviet Union. China today may be more concerned about spy activities conducted by the United States than a surprise attack, either from the United States or its South China Sea neighbors. If China wants to reduce U.S. surveillance activities along its coast, the capability to enforce is more important than the formal declaration of an ADIZ, since Washington has already declared it will neither recognize nor accept a Chinese ADIZ.

-ADIZ as an exclusion zone. An ADIZ can provide a legal basis for denying foreign aircraft access to certain areas. China’s ADIZ in the East China Sea requires even aircraft that transit the international airspace and not bound to China to identify themselves.

-ADIZ as a sovereignty marker. Although an ADIZ is not a territorial claim, it can be used to exercise some forms of sovereignty rights and administration over the airspace of a territory. Acceptance or acquiescence by foreign aircraft of an ADIZ then may be interpreted as recognition of the ADIZ-declaring state’s effective exercise of sovereignty over a territory. While an ADIZ must be enforced in order to function as an early warning mechanism or an exclusion zone, it does not need much enforcement to act as a sovereignty marker. Some poor enforcement may be enough to register the exercise of sovereignty and no actual enforcement is required to elicit recognition by foreign states.

-ADIZ as a bargaining chip. An ADIZ can be used to boost the position of the state that declares it in some game it plays with foreign states. China’s East China Sea ADIZ, for example, has strengthened Beijing’s position vis-à-vis Japan in their disputes over the Senkaku (or Diaoyu) Islands. It gave China a legal basis to scramble its jet fighters against Japanese planes in the region and broadened the area of physical dispute from the islands’ adjacent waters to airspace over the territory. The East China Sea ADIZ also helped China to create a new status quo in the region. As Ian Rinehart and Bart Elias argued, “The PRC would acquire strategic advantage by asserting a maximalist position, then seeming to back down, while preserving some incremental gain—akin to a ‘ratchet’ effect.”

-ADIZ as a signaling device. An ADIZ can be used to signal something important about the state that issues it. The audience of the signaling may be domestic or international or both. Declaring an ADIZ in the face of foreign opposition may signal resolve. It may also signal anger, and thus indirectly, formidability, when responding to a preceding event that hurts the ADIZ-declaring state. The enforcement of an ADIZ may signal capability. Resolve, anger and capability may act to deter foreign states from hurting the ADIZ-declaring state. Can an ADIZ be employed to reassure others of the declaring state’s cooperative intention? One observer argues that China tried to use its East China Sea ADIZ as an “instrument of engagement, not aggression.” However, the international opposition to both the East China Sea and the South China Sea ADIZ suggests that only a fool would use it to signal cooperation.

-ADIZ as a deterrent. Not only signals sent by the announcement of an ADIZ, but the serious possibility of an ADIZ can also act to deter others from doing things that the ADIZ-declaring state does not want. While the former function can only work after the ADIZ is declared, the latter will cease to work at that same moment. For an unborn and hypothetical ADIZ to serve as a deterrent, it has to be designed in ways that are highly detrimental to the interests of the deterred. With its possible functions as an exclusion zone, a sovereignty marker and a position booster, China’s ADIZ can serve as a deterrent. In fact, China has developed a consistent narrative on the South China Sea ADIZ, saying whether it will declare an ADIZ in the South China Sea depends on the threat level it faces.

When Will China Set Up an ADIZ in the South China Sea?

China’s decision to declare an ADIZ will most likely be the result of its cost-benefit calculation. If China has plans to declare an ADIZ in the South China Sea, it will likely make the announcement when the anticipated benefits exceed the anticipated costs. The benefits derive mainly from the utility of an ADIZ; the costs depend largely on foreign reaction. Circumstances such as a North Korea crisis that makes the United States depend on China’s support or an international court ruling on the South China Sea dispute could also influence this cost-benefit analysis. These international events may either tie the hands of China’s rivals or allow them to be more assertive in the South China Sea. They may also change the military, political, legal and diplomatic value that China can extract from a South China Sea ADIZ.

While the benefits are arguably more or less clear to China, the costs add a thick fog of uncertainty to the matter. It is generally hard to know how a foreign state will react, and China may well misread foreign signals. For outside observers, predicting whether and when China will announce a South China Sea ADIZ is a business that is bound to fail. Nevertheless, the uncertainty associated with this business is not unlimited—several factors set the parameters of Beijing’s decision.

If China wants to use a South China Sea ADIZ for military purposes (early warning and anti-access area denial), effective enforcement is a key requirement. The building of necessary infrastructure and the deployment of necessary assets are key indications of when China will set up its ADIZ. China may formally declare an ADIZ once its capabilities for enforcement are in place, but if the circumstances are not favorable, it may impose its early warning systems and exclusion zones under names different than ADIZ, or it may enforce them undeclared on a de facto basis.

If China employs its ADIZ as a “sovereignty marker” (to register sovereignty over the South China Sea territories and get international recognition or acquiescence), a bargaining chip, or a signaling device, a declaration is more important than de facto enforcement. The benefits of an ADIZ in these respects are potentially large, but the risks associated with a declaration are also significant. These risks are much higher than those associated with the declaration of China’s East China Sea ADIZ. As the South China Sea dispute involves more parties, a South China Sea ADIZ will turn more states against China. While the East China Sea ADIZ caught the world by surprise, a South China Sea ADIZ will not. This means that China’s rivals have time not only to think about their best reaction, but also to put pressure on China to prevent a South China Sea ADIZ. Still, these risks may plunge temporarily when a number of China’s rivals need its cooperation for a different issue of higher priority. Also, some circumstances may temporarily catapult the value of a South China Sea ADIZ as a bargaining chip or a signal of resolve. These moments will provide the best chance for China to declare a South China Sea ADIZ.

Size and Scope

If China imposes an ADIZ in the South China Sea, the maximum scope of this ADIZ will likely be roughly that of the nine-dash line. A larger scope will cause much additional opposition while bringing little additional utility. The cost-benefit ratio of an ADIZ varies with its scope. Essentially, China has six choices with the scope of a South China Sea ADIZ.

The smallest ADIZ would cover the Paracel Islands. This ADIZ can also include parts or whole of the Hainan Island. Such an ADIZ will have the smallest number of opponents. It will likely be opposed by Vietnam, which claims the Paracels and the United States, but it may avoid strong reaction from most other states.

In a second scenario, China can declare an ADIZ along its South China Sea coast, encompassing not just the Paracel Islands but also the Pratas Islands, which lie 180 nautical miles southeast of Hong Kong. As the Pratas are administered by Taiwan, an ADIZ that covers this territory will not only increase the number of opponents but also inadvertently create an opportunity for Taiwan to step up in the international arena.

A third version of a South China Sea ADIZ would stretch out from China’s southern coast and involve the Pratas, the Paracels, and Scarborough Shoal, which lies 100 nautical miles from the Philippine coast. This ADIZ will cause strong opposition from at least the United States, Vietnam, Taiwan and the Philippines.

In a fourth version, an ADIZ that covers only the Paracels and Scarborough Shoal can avoid provoking Taiwan but still turn the United States, Vietnam and the Philippines against Beijing.

A fifth choice is a full ADIZ that contains roughly all the area China claims in the South China Sea, including the Pratas, the Paracels, Scarborough Shoal, the Spratly Islands and the waters between and surrounding them. This ADIZ will have the largest number of opponents but also the largest benefits among the different versions of a South China Sea ADIZ. China can leave the Pratas Islands outside the full ADIZ, but this smaller version may not significantly reduce Taiwan’s opposition as it still involves the Taiwan-held Itu Aba Island in the Spratlys.

Finally, a sixth choice for China is to declare an ADIZ over the Spratly Islands with the possible coverage of Scarborough Shoal, but not the Paracel Islands. As all claimants of the South China Sea disputes are involved in the Spratlys, this ADIZ will still have the maximum number of opponents. However, it could significantly reduce the risks by avoiding a Vietnamese ADIZ over the Paracels. A Vietnamese ADIZ that encompasses the Paracel Islands can act as a Vietnamese sovereignty marker, allowing Hanoi to register some exercise of sovereignty and administration over an area where China is denying there is a dispute.

A “Red Line” or Just an “Orange Line”?

China’s possible ADIZ would not be the first ADIZ in the South China Sea. During the Cold War, a Philippine ADIZ was established in 1953, and a South Vietnamese ADIZ also existed until the end of the Vietnam War in 1975. However, the Philippine ADIZ is inoperative, while the South Vietnamese ADIZ is nonexistent even for the Vietnamese military of today.

On the contrary, a Chinese ADIZ in the South China Sea is perceived as highly threatening and intolerable. Vietnam’s top defense diplomat Nguyen Chi Vinh noted in a January 2014 interview that an ADIZ “would be more dangerous than even the nine-dash line” because it would come with more excessive regulations than the latter. Suggesting that China’s South China Sea ADIZ might be unacceptable to Hanoi, Vinh said in the same interview that it would “kill” Vietnam. Similarly but more bluntly, then Philippine Foreign Secretary Alberto del Rosario said during a joint press conference with his British counterpart in January 2016, “whether this [China’s South China Sea ADIZ] is done in terms of a de facto basis or it is official, this will be deemed unacceptable to us.” At the same press conference, British Foreign Secretary Philip Hammond stated, “Freedom of navigation and overflight are non-negotiable. They are red lines for us.” The United States’ official position is that an “ADIZ over portions of the South China Sea” would be “provocative and destabilizing.” U.S. Secretary of State John Kerry has repeatedly called for China not to declare an ADIZ there. Australia’s Foreign Minister Julie Bishop also urged China not to create the South China Sea ADIZ. In June 2016, Taiwan’s Defense Minister Feng Shih-kuan told lawmakers, “We will not recognize any ADIZ by China.”

While it is certain that several countries will defy China’s ADIZ in the South China Sea one way or another, it remains unclear whether the South China Sea ADIZ represents a “red line,” the passage of which will trigger formidable countermeasures. Nevertheless, foreign reactions to a Chinese ADIZ in the South China Sea will likely be harsher than what happened with Beijing’s East China Sea ADIZ, which can be likened with the yellow card in soccer. The South China Sea ADIZ appears to belong to a weaker sense of red line that can be called “orange line.” In this sense, an orange line represents a watershed between what is tolerable and what is not, but the response to what is intolerable may or may not be very fearsome.

Alexander L. Vuving is a Professor at the Daniel K. Inouye Asia-Pacific Center for Security Studies. This article is adapted from the author’s “Guide to the South China Sea ADIZ,” written for the South China Sea Chronicle Initiative. The author wishes to thank Cai Ngoc Thien Huong for her research assistance and Van Pham for her initiative of a larger project on China’s ADIZ. The views expressed in this article and any possible mistakes are the author’s own.

Image: The HMS Daring en route to the Philippines. LA(PHOT) Keith Morgan/MOD.