How to Respond to China’s Tactics in the South China Sea

The odds of armed conflict in the South China Sea are high and rising. China’s relentless assertiveness against the Philippines—harassing ships inside Manila’s internationally recognized Exclusive Economic Zone (EEZ), most notably at Second Thomas Shoal and Scarborough Shoal—has led to a situation where war in the South China Sea now seems more likely than at any other Indo-Pacific flash point, including the Taiwan Strait and Korean Peninsula.

To be sure, the Philippines’ security alliance with the United States has so far deterred China from more serious attacks on the Philippine military or other government assets. But the 1951 Mutual Defense Treaty—which commits Washington to come to Manila’s aid if the latter is under military attack—has utterly failed to deter Beijing from escalating its coercive gray-zone tactics—aggressive actions designed to irreversibly change the status quo without resorting to lethal force. These tactics have included ramming, shadowing, blocking, encircling, firing water cannons, and using military-grade lasers against civilian ships and military vessels. China also relies on its formidable coast guard and so-called fishing militia—comprised of fishermen who are trained and equipped by the military—to patrol, loiter in, and occupy disputed areas, establishing a quasi-permanent presence that the targeted country cannot easily dislodge.

On June 15, moreover, Beijing is reportedly planning to implement a new policy that would authorize the Chinese coast guard to detain foreigners crossing into waters claimed by China. These waters include most of the South China Sea—based on Beijing’s own expansive historical claims rather than international law, which in this case is the United Nations Convention on the Law of the Sea. (For comparison, imagine if Germany claimed the entire North Sea, or if the United States claimed the entire Caribbean right up to the South American coast.)

In the past, China has attempted to cordon off its claims with floating barriers and, most recently, is accused by Manila of building an artificial island at Sabina Shoal—150 kilometers (about 93 miles) from the Philippines’ Palawan Island, but 1,200 kilometers (746 miles) from the closest point in China. A well-informed source who asked to remain anonymous told me that Manila is already blocked from accessing approximately 30 percent of its recognized EEZ due to Chinese salami-slicing tactics. Absent an effective response, this percentage will only rise in the coming years.

In fact, China has the Philippines in an ever-tightening stranglehold that is increasingly compromising the latter’s sovereignty and territorial integrity at sea. If international law is to be upheld and borders are to remain inviolable, the United States must do more to help the Philippines. Yet neither Manila nor Washington seem to have a viable plan to counter Beijing’s successful gray-zone tactics.

Facing an increasingly desperate situation, in March, the Philippines announced a Comprehensive Archipelagic Defense Concept. Public details are scant, but it seems to be a new defense strategy that transitions away from Manila’s traditionally army-centric model—informed by a long history of invasions and occupations—toward upgrading the navy and coast guard to counter China at sea. Full funding for the new strategy is still pending in parliament. Regardless, the concept seems to ignore the equally important air force, and the entire process will take many years, if not decades, to implement.

In the meantime, Manila is pressing forward with three other efforts.

First, it is deepening its alliance with Washington. Earlier this month, the two countries carried out their largest-ever annual military drills, which included exercising the defense of an island chain in the northern Philippines (just 125 miles south of Taiwan) as well as a practice launch of an anti-ship cruise missile to sink a decommissioned ship. Since coming into office in 2022, Philippine President Ferdinand Marcos has raised the number of military bases that the U.S. military can temporarily use from five to nine, in line with the Enhanced Defense Cooperation Agreement signed in 2014.

Second, the Philippines has been forging ahead on a number of security drills and agreements with other countries in the region. Last month, for example, Australia, Japan, the Philippines, and the United States conducted joint exercises within Manila’s EEZ for the first time. Members of the group—known as the “new Quad” or “Squad”—are also negotiating new bilateral security agreements. Japan and the Philippines are discussing a reciprocal troop access agreement that should be completed by July. The Philippines and Australia have upgraded cooperation in maritime security and elevated their partnership to “strategic” following Marcos’s visit to Canberra in February. The Philippines is also receiving some arms assistance from India, such as a recent delivery of much-needed BrahMos anti-ship cruise missiles.

Finally, Manila recently adopted a strategy of “assertive transparency” toward Chinese encroachments into its EEZ. Philippine ship crews are now recording each incident of Chinese coercion and publicizing it for the world to see. The idea is that Beijing will no longer be able to deny its actions as it has done in the past—and perhaps be shamed into adhering to international law.

For its part, the United States has reiterated its “ironclad” commitment to the Philippines multiple times.

The problem is that the Cold War–era U.S.-Philippines treaty did not foresee the kinds of gray-zone tactics and hybrid threats that have become the modus operandi for revisionist states in recent years, whether in the South China Sea or on NATO’s eastern flank. Washington has not elaborated on what types of Chinese action might trigger U.S. intervention in support of its ally. The Biden administration has consistently noted that triggers include “armed attacks” on Philippine military or coast guard vessels, but it has not said what constitutes such an attack. Thus far, China’s aggressive but nonlethal actions against the Philippines do not appear to qualify.

As much as Manila, Washington, and their partners are now working to counter China, none of their steps has been effective in deterring Beijing’s increasing encroachments. What can the Philippines and the United States do—and is it even possible to restore deterrence in the South China Sea?

One option is to revise the U.S.-Philippines treaty to reflect modern gray-zone threats. Rather than vaguely highlighting an “armed attack” as the prompt for U.S. military intervention, Manila and Washington could broadly note that gray-zone activities could or would count as armed attacks.

During his visit to the Pentagon last month, for example, Marcos specified that “if any Filipino serviceman is killed by an attack from any foreign power, then that is time to invoke the [treaty].” The two countries could further broaden the category of assets covered by the treaty to include the civilian ships that regularly resupply Philippine troops stationed on the Sierra Madre, a World War II-era landing ship that Manila intentionally ran aground at Second Thomas Shoal in 1999. China might think twice about violating a revised, more encompassing defense clause.

There are other ways for Washington to clarify its policy in the South China Sea. In July 2020, then–U.S. Secretary of State Mike Pompeo stated that the United States recognized the legality and integrity of the sea’s EEZs in line with U.N. laws and the 2016 international arbitration ruling that rejected China’s expansive claims. To date, however, the United States has not taken an official position on the disputed territories within the South China Sea, perhaps to avoid antagonizing China further.

By contrast, the Obama administration clarified in 2012 that Washington recognized the Senkaku Islands as belonging to Japan, not China, in their East China Sea standoff, and that any attack on the islands would trigger Article 5 of the U.S.-Japan security treaty, meaning that the United States would be required to respond. Manila would obviously appreciate a similar clarification, which would signal to Beijing that Washington now considers attacks on the Philippines’ recognized EEZ to be direct assaults on its sovereignty and territorial integrity, which are already covered by the treaty.

Another option is for the U.S. military to play a more direct role in the region. Asia security expert Blake Herzinger recently argued that one way of bolstering deterrence and repelling China’s gray-zone tactics is to remove the Sierra Madre and replace it with a combined forward operating base used by both Philippine forces and the U.S. Marine Corps. Other researchers have argued for varying levels of U.S. involvement without establishing a base—such as combined naval or coast guard patrols—with the same aim of enhancing deterrence.

An intriguing technological solution might be to leverage the U.S. military’s ongoing Replicator program, scheduled to become available by August 2025. A product of the Pentagon’s Defense Innovation Unit, Replicator seeks (PDF) to quickly produce thousands of air and naval drones to make up for numerical shortfalls against the Chinese military. Although few details are public, the U.S. Defense Department is already introducing Replicator drones in the Indo-Pacific, and it may eventually be capable of swarming targets and possibly conducting a range of gray-zone activities of its own, though its capabilities for now remain classified.

Uncrewed systems such as Replicator could keep tit-for-tat encounters just below the threshold of triggering a broader war, especially because China’s own defense projects could also take the human element out of clashes at sea by using robotic and artificial intelligence–enabled warfare. Put another way, Replicator could help reset the escalation ladder and give China, the United States, and the Philippines greater space to negotiate after incidents.

Washington could also consider creating a linkage between China’s gray-zone actions against a U.S. ally and other areas of the U.S.-China relationship. That would signal to Beijing that its encroachments on the Philippines come with costs. These could include economic sanctions, postponement or termination of diplomatic negotiations, or changes to the U.S. military posturing elsewhere in the region. Imposing costs for aggressive actions would fit neatly into the Biden administration’s so-called integrated deterrence strategy, which seeks to leverage the collective, interagency strength of the United States, its allies, and its partners to respond to aggression.

As for collective action by the Association of Southeast Asian States (ASEAN) to challenge Chinese encroachments, the track record of the past nearly 30 years is not encouraging—even though several other members, including Vietnam and Malaysia, are also facing Chinese incursions into their waters. Since 1996, ASEAN has been working on a future code of conduct for the region, which might call for an end to militarization, land reclamation, and seizures of disputed features. However, this would entirely depend on the bloc’s success in negotiating the code with Beijing, which has shown no inclination to compromise on its view that it owns most of the South China Sea. Bilateral negotiations would likely founder for similar reasons.

Finally, Washington and Manila could simply stay the course. This would mean continuing to bolster the alliance through expansion of the existing defense cooperation agreement, more focused annual military exercises, and other engagements, as well as through helping Manila to build its own military capabilities and expose China’s bad behavior to the world. But none of these measures have been successful against gray-zone tactics so far, and any future success is likely to take more time as Beijing continues to eat away at Manila’s EEZ.

The best option might be to stay the course on U.S.-Philippines alliance-building but add new features, such as revising the treaty to reflect gray-zone realities, tie into the Replicator program, and impose costs for China’s behavior via other parts of the U.S.-China relationship. Doing these things now should give the Philippines the breathing room that it needs to modernize and professionalize its military with U.S. assistance, helping to reestablish deterrence and lessen the risk of war in the years to come.

By: Derek Grossman  – a senior defense analyst at RAND, an adjunct professor at the University of Southern California, and a former daily intelligence briefer to the U.S. assistant secretary of defense for Asian and Pacific security affairs.