A Chinese coast guard ship attached itself like a shadow to a group of boats from the Philippines, trailing them for hours.
The Philippines had sent two wooden boats and two coast guard vessels to resupply an unusual outpost in the South China Sea: a decrepit World War-II era ship preventing Beijing from taking control of a reef called Second Thomas Shoal.
The encounter that followed—reconstructed via ship-tracking data from maritime analytics provider MarineTraffic—shows in vivid detail how China tries to enforce its will in the South China Sea. The tactics have led to increasingly tense confrontations, with the potential to draw in the U.S., a treaty ally of the Philippines.
At least 15 Chinese ships took up positions near Second Thomas Shoal on Oct. 22. As the convoy from the Philippines approached, the Chinese ships burst into a flurry of maneuvers: darting around, circling, cutting across bows. They outnumbered the Philippines 4-to-1.
The first collision occurred 6 nautical miles from the reef’s mouth. A Chinese coast guard ship hit one of the Philippine boats carrying supplies for the outpost, prompting it to abort its mission. Two hours later, a Chinese militia boat bumped a Philippine coast guard ship.
The events that day were part of a playbook for China, which uses its overwhelming numbers and outposts in the South China Sea to pressure rivals. On short notice, Beijing’s fleets can move rapidly—even hundreds of miles from its own shores—to swarm and obstruct opposing ships.
China’s ability to sustain such a presence has vastly reshaped the South China Sea. It projects power across the strategic waterway, squeezing others and turning routine patrols into perilous operations.
China’s actions lie in the gray zone—not all-out war, but not peace either. Rather than attention-grabbing gray-hulled warships, Beijing deploys its coast guard and maritime militia, the largest such fleets in the world. The militia is often state-funded and well-trained, acting in close concert with the coast guard and drawing support from Chinese bases such as Mischief Reef, as the Oct. 22 incident demonstrated.
China deploys these two forces on the front lines in the South China Sea to gain the numerical upper hand it needs to awe and overwhelm its rivals. Patrolling a long way from mainland China and demonstrating an unmatched presence, the coast guard and maritime militia block, swarm, shadow and warn opposing ships.
They are the chief enforcers of China’s vast claims in the South China Sea—and the reason it has been able to expand its control without firing a shot.
A militia scrum can be seen regularly near Philippine-controlled Thitu Island, making it evermore difficult for Filipino fishermen to operate there. Further north, militia ships team up with China’s coast guard for a round-the-clock blockade of Scarborough Shoal, preventing Filipinos from accessing traditional fishing grounds. To the west, Chinese ships have shadowed and threatened Vietnam’s offshore oil-and gas-operations, making commercial investments fraught with risk.
China’s ability to respond, hundreds of miles from its southern coast with speed and intensity, is rooted in the areas it has already occupied in the South China Sea. MarineTraffic data showed that the ships that responded to the Philippines’ resupply mission on Oct. 22 were deployed from Mischief Reef, located 17 nautical miles northwest of Second Thomas Shoal.
A decade ago, Mischief Reef was nothing more than a smattering of land peeking above the water at low tide. China first built it into an island, then a military base, equipped with missiles, radar and a runway.
Now, Mischief Reef is a base of operations for Chinese ships—a staging area—for the southern part of the South China Sea. They don’t need to make two- or three-day journeys to distant ports in China to rest and refuel. Instead, they spend weeks or months at Mischief Reef, policing the waters for activities China deems illegal, tracking Philippine movements and reacting to them.
Each time Filipino crews leave port for a resupply mission to Second Thomas Shoal, they know that China will be waiting for them, and in larger numbers.
“What China has guaranteed itself is that, basically, it can always have overmatch over anything the Philippines can send out—almost at a moment’s notice,” said Raymond Powell, director of an initiative called SeaLight, which tracks China’s gray-zone activities, at Stanford University’s Gordian Knot Center for National Security Innovation. Without Mischief Reef, China “wouldn’t be able to intercept them with nearly the level of force that they’re able to send,” he said.
China has two other such bases in this part of the South China Sea, Subi Reef and Fiery Cross Reef, which help Beijing sustain surge forces that can be deployed to various hot spots.
Beijing says its actions in the South China Sea are aimed at safeguarding China’s sovereignty and maritime rights and are beyond reproach. Its position is rooted in history, it says, and it accuses the U.S. of interfering in the region, sowing discord and stoking trouble.
China is using its fleets and bases to expand its hold over the South China Sea, including at Second Thomas Shoal. The teardrop-shaped reef is more than 600 nautical miles from China and just over 100 nautical miles from the Philippines—and within the country’s exclusive economic zone that gives it the right to exploit resources under international law.
The Philippines grounded a ship, the BRP Sierra Madre, on the reef nearly 25 years ago. The ship has become a precarious garrison—leaky and covered in rust—with a small detachment of marines aboard. No one knows how much longer it can hold up.
Beijing says the Philippines promised after the 1999 grounding to tow away the ship, but hasn’t. It accuses Philippine vessels of illegally intruding to deliver construction materials for the ship’s repair, even though those vessels are too small to carry the volume of materials needed to undertake anything more than small-scale fixes.
This year, Beijing has stepped up aggressive activities around Second Thomas Shoal. Chinese ships have flashed a military-grade laser and fired a water cannon at Philippine ships. Their actions on Oct. 22 drew swift criticism from a host of nations including the U.S., which called the moves dangerous and unlawful.
President Biden said after the incident that the U.S. mutual-defense treaty with the Philippines was ironclad. Defense secretaries from the two sides spoke about China’s actions, as did their national-security advisers.
Three senior U.S. senators, in a late-October letter to Biden, urged him to outline plans to support Philippine efforts to resupply the Sierra Madre. China’s actions are testing the credibility and value of the U.S.’s commitments to its Southeast Asian ally, and America must respond with strength, they said.
China’s main purpose is to force the Philippines to abandon Second Thomas Shoal and take de facto control of the feature, the senators wrote, adding: “Doing so would expand further its unlawful maritime claims.”
One Philippines resupply vessel got through on Oct. 22. A complete blockade would threaten the survival of the Filipino marines on the Sierra Madre, opening up Beijing to severe international criticism. Security experts say China’s show of force is designed instead to warn the Philippines against going further—for example, by refurbishing the Sierra Madre or building permanent structures on Second Thomas Shoal.
That is a problem for Manila because the time is coming, the experts say, when it will no longer be able to stand—at least not without major renovation.
If the Sierra Madre began disintegrating, China would likely send its ships in, possibly under the pretext of rescuing the Filipino marines. The worst-case scenario for the Philippines: China seizes the initiative, rushing ships from Mischief Reef and taking control before its adversaries can react.
China has “such a preponderance of forces there that without immediate aid from an outside power like the U.S. or others, it’s not clear what the Philippines would do,” said Powell of the SeaLight initiative. “And even with aid from an outside power, it’s not clear how that would work.”
The Philippines says it has a duty to repair the ship, which remains a commissioned navy vessel. “They cannot tell us what to do in our own backyard,” said the country’s military spokesman, Col. Medel Aguilar.
Adm. Rommel Ong, who retired in 2019 as a vice commander of the Philippine navy, said the Philippines should act before a crisis erupts. It could build a platform or some other type of structure on the reef, Ong said. Grounding another ship is also an option, though a stopgap one like it was the first time around, he said.
Any such moves, however, would meet with stiff Chinese resistance.
“There will have to be a decision made to repair or replace Sierra Madre,” Ong said. “Otherwise we will lose control of Second Thomas Shoal.”
Write to Niharika Mandhana at niharika.mandhana@wsj.com