Two recent developments suggest that China is preparing to take preemptive action in the South China Sea in advance of the ruling by the Arbitral Tribunal at the Permanent Count of Arbitration (PCA) in The Hague on claims against it brought by the Philippines. (That ruling is expected in late-May or June.)

These developments include beefing up air defenses on Woody Island in the Paracels, and, moreover,  leaked intelligence assessments that China may be planning major construction activities at Scarborough Shoal.

Satellite imagery taken on April 7 revealed that China recently deployed two additional Shenyang J-11 multirole jet fighters and the Active Electronically Scanned Array or AESA system to Woody Island. Pentagon officials estimate that China has about ten military aircraft stationed there, including J-11s and Xian JH-7s. The J-11 is an air superiority fighter, similar to the Russian Su-27, with a range of 3,530 km, according to the journal Air Force Technology. The JH-7 is a fighter bomber.

In February this year China placed eight batteries of the HQ-9 surface-to-air missile system on Woody island;four are currently operational. These missiles have a range of nearly 220 km. Now that China has deployed the AESA fire control radar it will be able to more accurately monitor aircraft movements around Woody Island. The AESA system tracks multiple targets at the same time and gathers data on the target’s range, altitude, direction and speed in order to direct the HQ-9 missiles.

There are three likely explanations for China’s action.

First, China is reacting to the activation of the Enhanced Defense Cooperation Agreement between the Philippines and the United States. In March the Philippines released the names of four air bases and one army base that will be open to the rotation of U.S. military personnel, planes and equipment. Also in March the Philippines and the U.S. began conducting joint naval patrols in the South China Sea. Joint air patrols are expected to commence this month.

China also is angered at the current Balikatan (Shoulder-to-Shoulder) military exercises underway in the Philippines involving U.S., Australian, and other military forces and the accompanying visit by U.S. Defense Secretary Ashton Carter to the Philippines. After the conclusion of Balikatan six military aircraft (including five Warthog ground-attack planes) and three helicopters will remain at Clark Air Force Base along with 200 pilots and crew.

Second, China also may be reacting to recent reports that the next U.S. Freedom of Navigation Operational Patrol in the South China Sea will take place shortly, following a first operation in the Spratlys in October 2015 and another in the Paracels in January 2016.

Third, China likely is responding to the G7’s adoption of a special statement on maritime security. Thisstatement declared:

We express our strong opposition to any intimidating, coercive or provocative unilateral actions that could alter the status quo and increase tensions, and urge all states to refrain from such actions as land reclamations including large scale  ones, building of outposts, as well as their use for military purposes and to act in accordance with international law including the principles of freedoms of navigation and overflight.

China strongly condemned the G-7 statement.

In the longer term, China’s deployment of fighter aircraft and fire control radar to the Paracels demonstrates its capability to deploy small numbers of modern jet aircraft, surface-to-air missiles, and fire control radar at short notice to airstrips elsewhere in the South China Sea and that the United States can take no action to prevent it from doing so. China also is sending a signal to the United States that the risks have gone up if the United States continues to conduct aerial reconnaissance of sensitive Chinese military installations and fly over People’s Liberation Army Navy (PLAN) warships in the South China Sea.

U.S. intelligence sources confirmed last month that China had drawn up plans for a new phase of militarization involving Scarborough Shoal. The Australian media has reported similar concerns by Australian intelligence and analytical agencies, presumably Australia’s Defense Intelligence Organization and the Office of National Assessments, that China is poised to take “decisive and provocative action” in the Spratly Islands. These sources report that China may dynamite Scarborough Shoal to build an artificial island to house military facilities or declare an Air Defense Identification Zone (ADIZ). China declared an ADIZ in the East China Sea in November 2013.

If these reports are accurate, China is likely to erect small permanent structures on Scarborough Shoal and station personnel on them. China would justify its actions under the guise of providing public goods such as weather reports and safety of navigation. By acting quickly China would leave the United States and the Philippines flat footed. This would lay the ground work for further expansion in the future.

Once the Arbitral Tribunal makes its finding public, China is likely to mount an international campaign challenging the legitimacy of the Tribunal. Australia got a foretaste of China’s likely propaganda offensive when leaders of the Australian Chinese community convened a forum on April 9 in Sydney. The Diplomat received a translated copy of an official statement released by Australian Chinese community leaders. It stated that:

…the Australian political elite should have a sober understanding of these matters and should treat carefully on sensitive matters like the South China Sea. They should not send irrational and mistaken signals to the international community.

The statement also called on Australian political circles to “make appropriate preparations for a possible ‘crisis situation.’”

The meeting by Australia-Chinese community leaders took place on the eve of Malcolm Turnbull’s first visit to Beijing as prime minister. Prior to Turnbull’s departure the media reported that he would raise his concerns over the South China Sea privately to Premier Li Keqiang and President Xi Jinping in Beijing.

Turnbull was greeted on arrival in Shanghai with a news report in the China Daily that quoted a member of the Chinese Academy of Social Sciences as stating that the South China Sea dispute “will cast a shadow on the promising (economic) cooperation if such a tendency keeps developing.” This was viewed as a veiled warning that Australia’s economic interests could be harmed by its South China Sea policy. Earlier in March, Turnbull characterized China’s South China Sea policy as “counterproductive.”

If China converted Scarborough Shoal into an artificial island and constructed an airfield and harbor, it would have the basic infrastructure to prevent the Philippines from operating in the waters of the Spratly islands, leaving Pag-asa island and Second Thomas Shoal exposed.

If China placed long-range radar, fire control radar, surface-to-air missiles, and anti-ship cruise missiles on its artificial islands, including Scarborough Shoal, it would be in a much better position to monitor the movements of U.S. Seventh Fleet vessels using Subic Bay, for example.

The U.S. Navy and other regional navies would be placed at risk in a crisis situation in the South China Sea. China would have excellent maritime domain awareness and be able to respond to the intrusion of foreign military ships and aircraft once it completed the construction of airfields, protected hangars, and fuel storage facilities.

China’s J-11 multirole air superiority fighters could take off from Woody Island to conduct combat air patrols. They could extend their patrol time by landing and refueling on an airfield on one of the artificial islands.

China has constructed and continues to construct helipads on its occupied features. This would enable China to monitor U.S. submarines through the deployment of aerial reconnaissance aircraft and anti-submarine warfare helicopters.

If China undertakes “decisive and provocative” action by shoring up its position on Scarborough Shoal,  it would present a fait accompli to findings of the Arbitral Tribunal. The Tribunal has no power of enforcement. China’s pre-emptive actions would likely derail any concerted action by the international community to exert diplomatic pressure on China to respect international law by accepting the findings of the Arbitral Tribunal. Concerns about international law would be sidelined by China’s newest phase of militarization.