Demystifying China’s Gray Zone Aggression: Water Cannons, Ramming, and the Use of Force

Introduction

On May 21, 2025, a China Coast Guard (CCG) cutter  fired its water cannon and sideswiped the BRP Datu Sanday  twice, as the Bureau of Fisheries and Aquatic Resources vessel was legally collecting marine data samples near Sandy Cay Reef in the South China Sea. The CCG’s “aggressive inference, dangerous maneuvers, and illegal acts” damaged the civilian research vessel’s port bow and smokestack, putting at risk the lives of its crew.

China blamed the Philippines for the collision, indicating that the DA-BFAR vessel had “illegally intruded” Chinese waters without permission and ignored warning from the CCG vessel. The Philippine survey ship “dangerously” approached and collided with the CCG vessel, which was conducting normal law enforcement operations in the waters off Sandy Cay. In April, Chinese state media CCTV reported that China’s coast guard had “implemented maritime control” over Tiexan (Sandy Cay) Reef.

The U.S. Ambassador in Manila, MaryKay Carlson, condemned the CCG’s “aggressive actions against a lawful civilian mission near Sandy Cay,” which “recklessly endangered lives and threaten regional stability.” Ambassador Calson further indicated that the United States stands “with our Philippine allies in support of international law and a free and open Indo-Pacific.” These assurances are consistent with prior Biden and Trump administration notices to China that the United States is obligated under the Mutual Defense Treaty “to defend the Philippines if Filipino forces, ships and aircraft come under an armed attack, including in the South China Sea.” Despite these strongly worded statements, the United States has done little to actively assist the Philippines enforce its legitimate claims in the South China Sea against Chinese aggression.

China’s Illegal Claims

Incidents between China and the other South China Sea claimants is a common occurrence, as China attempts to solidify its unlawful claims over the Spratly Islands and surrounding waters, despite an arbitral tribunal decision that held China’s claims were illegal. To address Chinese transgressions, the Philippines initiated arbitration proceedings against China in 2013 pursuant to the United Nations Convention on the Law of the Sea (UNCLOS) (tribunal decision, ¶ 28). Although China is a party to UNCLOS and is therefore subject to the compulsory dispute settlement provisions of the Convention, China refused to participate in the proceedings.

The Philippines requested the Tribunal determine (inter alia) the validity of China’s claimed historic rights based on the Nine-Dash Line in the South China Sea. The Philippines additionally requested that the Tribunal determine (inter alia) that China’s actions against the Philippines and Philippine nationals violated China’s obligations under UNCLOS and other international conventions (tribunal decision, ¶¶ 7-10). On July 12, 2016, the Tribunal issued a unanimous award in favor of the Philippines invalidating China’s notorious Nine-Dash Line claim and ruling (inter alia) that CCG purported law enforcement operations, including use of blocking and other harassment maneuvers, “created serious risk of collision and danger to Philippine ships and personnel” (tribunal decision, ¶ 1203). Accordingly, the tribunal concluded that CCG law enforcement operations breached China’s obligations under the 1972 Convention on the International Regulations for Preventing Collisions at Sea (COLREGS), as well as Article 94 of the Convention (tribunal decision, ¶ 1203).

Although the decision is final and binding on both parties, China has refused to comply with the Tribunal’s decision, stating that the Award is “null and void” and has “no legal binding force” on China. Despite China’s untenable position regarding the Tribunal’s Award, CCG law enforcement operations in the waters around Sandy Cay and other South China Sea features are therefore invalid as a matter of law as China lacks jurisdiction in the relevant waters.

China’s So-Called Gray Zone Operations

Despite the illegality of China’s law enforcement operations, the international community (in general), and the Philippines and the United States (in particular), have failed to take adequate measures to challenge China’s aggression in the South China Sea. States excuse their lackluster response to this aggression by arguing that China is engaged in gray zone operations that fall below the threshold of a use of force warranting a response in self-defense by an aggrieved state. This misplaced reliance on the concept of gray zone operations, which is rooted in the International Court of Justice’s (ICJ) dubious decisions in the Nicaragua and Oil Platforms Cases, undermines deterrence and facilitates and encourages China’s continued use of coercion and aggression to advance its illegal claims in the South China Sea.

All states agree that states may legally use force in self-defense so long as the force used is necessary and proportionate to the nature of the threat being addressed. Nevertheless, there is an ongoing debate regarding whether states may exercise their right of self-defense against any illegal use of force or only against an “armed attack,” as reflected in Article 51 of the UN Charter. In Nicaragua v. United States, the ICJ concluded that, in determining whether the use of force in self-defense is legally justified, it is “necessary to distinguish the most grave forms of the use of force . . . from other less grave forms.” Accordingly, a State may only exercise its right of self-defense against the “most grave” forms of use of force—“those constituting an armed attack.”

The ICJ reached a similar conclusion in the Oil Platforms case. Specifically, the court found that the U.S. attacks on Iran’s oil platforms could only be justified as an exercise of self-defense if the United States showed that it had been attacked by Iran “and that those attacks were of such a nature as to be qualified as ‘armed attacks’ within the meaning of . . . Article 51.” Iran had used the derelict platforms to direct attacks against international shipping. The Court held that the U.S. defensive strikes against Iran’s oil platforms in the Persian Gulf constituted an unlawful use of force because Iranian actions against U.S. vessels were below the threshold of sufficient gravity required to warrant the use of force in self-defense.

These decisions reflect a social justice rationale that disadvantages powerful (developed) states while empowering weaker (developing) states and non-state actors. The result is that the ICJ inadvertently aids efforts to change the status quo through gray zone operations that fall below the threshold of an armed attack. Thus, rather than deter the aggressive use of force in international relations, the court’s decisions have the opposite effect of encouraging rogue states to use force, albeit below the threshold of an armed attack, to illicitly change the status quo and advance their national interests. By engaging in malign activities that fall below the threshold of an “armed attack,” revisionist states like China, Russia, North Korea, and Iran believe they can conduct unrestrained gray zone operations without being subject to a decisive military response.

Although most states, including U.S. partners and allies in the Asia-Pacific region, subscribe to the “Gap Theory,” the United States considers that customary international law allows States to exercise the right of self-defense against any illegal use of force. States that adhere to the “Gap Theory” believe that not all uses of force constitute an “armed attack” and do not trigger the right of self-defense under article 51 of the UN Charter. Only the most grave uses of force constitute and “armed attack,” thereby authorizing a state to use force against another state in self-defense. Consequently, if the United States and like-minded states seek to curtail China’s gray zone operations in the Indo-Pacific region, they must change the narrative by reassessing the applicability of the “Gap Theory” to uses of force that have heretofore been considered to fall below the threshold of an armed attack—e.g., use of waters cannons and intentional ramming.

Water Cannon Use as a Grave Use of Force

Water cannons are normally considered non-lethal weapons and are routinely used as crowd-control weapons by numerous states. They are also used at sea by coast guards and naval units to conduct legitimate maritime law enforcement operations. These weapons use streams of water to disperse crowds or limit access to an area. These streams of water can either be high-pressure, designed to push back a crowd or block a vessel, or low-pressure, intended to douse the target.

High-pressure water cannons have flow rates of up to 20 liters of water per second, operate at pressures up to 220 pounds per square inch, and can stream water up to 67 meters away. Thus, high-pressure, high-volume water cannons (like those used by the CCG) can damage property and knock a person down or push an individual back with significant force, “particularly when this pressure is sustained and exerted over a wide surface area.” Depending on how they are used, these weapons can therefore cause significant property damage or severe injury or death.

There are numerous reported instances where high-pressure water cannons have directly or indirectly caused serious injury, to include trauma to the body (e.g., organ damage), broken bones, internal injuries, head injuries (e.g., skull fractures), or facial injuries (e.g., blindness, eardrum rupture). Fatalities can also occur from falls after being knocked down by a water stream or from traumatic injuries caused by the force of the water. Thus, even though they are considered to be “non-lethal weapons, water cannons are capable of causing severe physical harm or death depending on how they are used. Although it is impossible to catalogue all incidents involving CCG use of water cannons against foreign ships in the South China Sea, there are several recent incidents that illustrate how the use of such weapons has caused serious injury to crew members and significant damage to their vessels.

In early March 2024, CCG cutters unleashed a water cannon attack on a chartered resupply vessel, the Unaizah May 4, and the Philippine Coast Guard (PCG) Parola-class patrol boat BRP Sindangan (MRRV-4407) that were attempting to resupply Filipino Marines on the BRP Sierra Madre (LT-57) at Second Thomas Shoal. The attack injured four Filipino sailors and shattered the resupply vessel’s windshield.

A few weeks later, the Unaizah May 4 was attacked again by CCG vessels near Second Thomas Shoal. Two CCG vessels repeatedly used high-pressure water cannons and hazardous blocking maneuvers against the Philippine vessel causing it to go dead in the water. The attack resulted in injuries to three Filipino sailors on board and caused significant damage to the vessel. Filipino military authorities apparently considered both of these incidents to have been an armed attack, awarding the three injured sailors the Wounded Personnel Medal, which is given to military personnel who “risk their lives during combat,” and the Military Merit Medal to a sailor injured during the March 5 incident for “heroic achievement in combat.”

A third incident occurred at Second Thomas Shoal in June 2024. Philippine vessels involved in the attempted resupply of the BRP Sierra Madre were damaged and a Filipino sailor was injured when CCG patrol boats engaged in “dangerous and deliberate use of water cannons, rammings, and blocking maneuvers” to prevent resupply of the outpost.

These incidents confirm that CCG use of high-pressure water cannons against ships and their crews can cause significant property damage and serious bodily injury to personnel. Thus, such use constitutes a grave use of force that warrants a proportionate response in self-defense.

Ramming as a Means of Warfare

Although the term “means of warfare” is not defined in any treaty, it is closely linked to the notion of “attack”—that is, acts of violence against an adversary that occur during armed conflict, the effects of which include injury, damage, destruction, or death. An object qualifies as a “means of warfare” if it is designed to produce, or intended to produce, such effects. Naval rams or ram ships have been historically used as a means of warfare for millennia. Ships, fitted with hardened and reinforced hulls or a bow prolongation, were intentionally steered directly into another vessel to damage or sink it.

The first recorded use of the naval ram dates to 535 BC during the Battle of Alalia. Greek ramming attacks against the Persian fleet turned the tide at the Battle of Salamis in 480 BC, one of the most important naval engagements in ancient history. Rams were also used throughout Europe and Asia during the Middle Ages. At the Battle of Lepanto in 1571, the Christian fleet of 206 galleys and 6 galleasses was pitted against an Ottoman fleet of 222 war galleys and 56 galliots. Most vessels on both sides were equipped with naval rams.

Ramming as a means of warfare at sea became less prevalent during the age of sail but regained its prominence in the 19th century as wooden ships were replaced by ironclads. Ramming was particularly prevalent during the American Civil War. In 1862, for example, the CSS Virginia rammed and sank the USS Cumberland while the Union sailing sloop was at anchor near Newport News. The next day, the Virginia rammed the USS Monitor causing minor damage to the Union ironclad. The following year, the French Navy commissioned its first coastal battleship—the Taureau—with a ram. Three years later, the Austrian fleet defeated the far superior Italian fleet at the Battle of Lissa by charging the Italian line and ramming the enemy vessels.

Ramming (by warships and merchant vessels) was also used during the First and Second World Wars, particularly against submarines. Nineteen German submarines were sunk by ramming during the First World War. Unarmed merchant vessels were also encouraged by the British Admiralty to ram enemy submarines. Germany lost three U-boats to ramming during the Second World War, Italy lost two, and Japan one. A Soviet submarine was also rammed and sunk by a Finnish submarine, and an Italian destroyer rammed and sunk a British submarine in the Mediterranean.

In short, naval ramming has been a means of warfare for over 2,500 years. It should, therefore, come as no surprise that China is engaging in this ancient form of warfare. People’s Armed Forces Maritime Militia (PAFMM) vessels engaged in intentional ramming are primarily based in the Paracel Islands. The Sansha PAFMM operates more than 80 ships equipped with water cannons and fitted with reinforced steel hulls purpose-built for ramming. Again, it is impossible to catalogue all ramming incidents involving PAFMM and CCG units in the South China Sea, but the following incidents highlight China’s use of intentional ramming as a means of warfare.

• In May 2014, forty steel-hulled PAFMM vessels surrounded a group of wooden-hulled Vietnamese fishing boats. One of the Chinese vessels intentionally rammed and sank a Vietnamese fishing boat. The Chinese vessels made no effort to rescue the ten crew members that went into the water. The crew was subsequently rescued by other Vietnamese fishing boats in the area. The president of the Vietnamese Fisheries Association called the “brutal and inhumane” incident an act of “attempted murder.”
• On September 29, 2015, a PAFMM vessel reported rammed a Vietnamese fishing vessel near the Crescent Group in the Paracels while its crew was asleep. The Chinese crew then boarded the fishing boat before it sank, beat the crew with electric batons, and stole seafood and fishing gear worth tens of thousands of U.S. dollars. As the PAFMM vessel departed the area, it ignored the fishermen’s request for rescue.
• In March 2019, a PAFMM vessel intentionally rammed a Vietnamese fishing boat near Discovery Reef in the Paracel Islands, causing the boat to capsize. The five crew members were left clinging to the bow of their overturned vessel until they were rescued by another Vietnamese fishing boat more than two hours later.
• In June 2019, a PAFMM vessel rammed and sank a Filipino fishing boat that was anchored near Reed Bank in the South China Sea. The Chinese vessel fled the scene without attempting to rescue the twenty-two crew members that went into the water. The crew was later rescued by a Vietnamese fishing boat.
• In April 2020, a Vietnamese fishing boat sank near the Paracel Islands after being rammed by a China Maritime Surveillance Vessel. The eight Vietnamese crew members were rescued by a Chinese fishing boat.
• In June 2020, a Vietnamese fishing boat operating near Lincoln Island in the Paracel was rammed by a PAFMM boat, forcing the crew of 16 to jump overboard. The crew was able to reach the shore with the assistance of other Vietnamese fishermen in the area.
• Also in June, a steel-hulled Chinese vessel repeatedly rammed a Vietnamese fishing boat, causing four crew members to fall overboard and forcing the rest of the crew to abandon ship. The ship was lost with several hundred pounds of tuna, mackerel, grouper, and flying fish on board.
• On June 18, 2024, a CCG vessel intentionally rammed a Philippine vessel on a resupply mission to Second Thomas Shoal. Several naval personnel on board were injured and one sailor had his thumb

Although none of the rammings resulted in a fatality, they did cause significant property damage, as well as serious injury to several crew members. Thus, intentionally ramming a wooden-hulled fishing boat with a ship fitted with a hardened and reinforced steel hull constitutes a grave use of force that warrants a proportionate response in self-defense.

Conclusion

China is exploiting the gap created by the misguided ICJ opinions to change the status quo and solidify its illegal claims throughout the Indo-Pacific region. It’s time to change the narrative and hold China accountable for its aggressive behavior by equating some ramming incidents and the use of water cannons as a grave use of force that warrants a kinetic response in self-defense.

If the physical consequences of a ramming or use of water cannon result in the kind of physical damage or injury caused by the kinetic use of force (e.g., naval mine attack, firing a missile, torpedo attack, dropping a bomb, etc.), the ramming or use of water cannon constitutes a grave use of force authorizing the aggrieved state to use proportionate kinetic force in self-defense. Although not all use of water cannons or ramming will warrant a kinetic response in self-defense, use of high-pressure water cannons at close range and ramming with vessels equipped with reinforced and hardened hulls can reasonably be expected to result in extensive property damage to the boat and death or serious bodily harm to its crew. In these circumstances, the aggrieved state is justified in using necessary and proportionate kinetic force in self-defense.

Of course, there are risks associated with using kinetic force in response to CCG and PAFMM aggressive behavior. Beijing may consider such a response as escalatory and retaliate with overwhelming force by the People’s Liberation Army-Navy. In the case of the Philippines, however, this risk could be mitigated by a clear statement indicating that Washington considers ramming and the use of water cannons that result in death, serious injury, or extensive property damage as an armed attack that falls within the scope of the collective self-defense provisions of the U.S.-Philippine Mutual Defense Treaty. Article IV of the treaty provides that “each Party recognizes that an armed attack in the Pacific Area on either of the Parties would be dangerous to its own peace and safety and declares that it would act to meet the common dangers in accordance with its constitutional processes.” For the purpose of Article IV, “an armed attack on either of the Parties is deemed to include an armed attack on the metropolitan territory of either of the Parties, or on the island territories under its jurisdiction in the Pacific or on its armed forces, public vessels or aircraft in the Pacific” (Article V).