Over the last two years, tensions between China and the Philippines at Second Thomas Shoal have emerged as the focal point of frictions in the South China Sea.

The Philippines maintains a detachment of marines at Second Thomas Shoal stationed aboard the BRP Sierra Madre, a Philippine navy ship intentionally grounded there in 1999. Ever since, the Philippines has maintained regular “rotation and resupply” missions to deliver supplies and rotate troops to and from the makeshift outpost.

China has maintained a regular coast guard patrol around Second Thomas since 2013 and has harassed Philippine resupply missions from time to time ever since. Most famously, in 2014, China blockaded the Sierra Madre for three weeks, forcing the Philippines to airdrop supplies. Since 2022, however, Chinese coast guard and militia ships have sought to block resupply missions more regularly, amassing around the shoal in greater numbers and employing increasingly aggressive tactics to prevent Philippine vessels from reaching the Sierra Madre. China justifies this behavior by accusing the Philippines of ferrying in construction supplies with the aim of either turning the Sierra Madre into a more permanent structure or building an entirely new outpost on Second Thomas.

Philippine and Chinese ships maneuver during a resupply mission to Second Thomas Shoal on November 10, 2023

Efforts by China to block Philippine resupply missions have made headlines as collisions and the use of water cannons have created fear that an incident at Second Thomas could spark a more serious conflict. But amid constant reports of confrontation between Philippine and Chinese ships, it can be difficult to discern whether the latest round of tensions is any different from those that occurred three years ago.

A Look at the Data

To better understand the evolution of recent tensions at Second Thomas Shoal, AMTI combined public reporting with a review of historical Automated Identification System (AIS) data to better analyze resupply missions since 2021. This time-period was chosen because of the availability of AIS data and does not include reported incidents around the shoal from 2013 to 2020, of which there were several. Over the three-year period, AMTI can identify 30 Philippine resupply missions: 18 that were both reported publicly and visible on AIS, 9 visible on AIS but not reported, and 3 reported but not visible on AIS.

This data is inherently incomplete. Ships using short range AIS transponders or those that turn their transponders off cannot be tracked on commercial satellite AIS platforms. This means that there are likely resupply missions that occurred but do not exist in this dataset, especially in 2021 and 2022 before the Philippines began regularly publicizing each mission. Nevertheless, a comparative analysis of this data over time reveals several major trends about tensions at Second Thomas Shoal.

1. The number of Chinese vessels involved has increased over time, and did so dramatically in 2023.

The number of Chinese vessels at Second Thomas Shoal during Philippine resupply missions has increased substantially. In 2021, on average, a single Chinese ship was observed at Second Thomas during resupply missions. By 2023, this increased to approximately 14 ships.

In contrast, the Philippines has averaged just 2-3 vessels present during resupply missions from 2021 through the end of 2023. This increase in Chinese vessels has been particularly dramatic in recent months: 46 Chinese ships were present at the most recent resupply mission on December 10, 2023, compared with just 4 for the Philippines.

2. The ships involved have shifted to include more military and paramilitary vessels

The types of vessels deployed to Second Thomas by both China and the Philippines have evolved over the past three years.

In 2021, Chinese maritime militia were not regularly deployed to Second Thomas. Instead, only a single China Coast Guard (CCG) vessel was present during most resupply missions. AIS data from April and May 2021 show Philippine government vessels from the Bureau of Fisheries and Aquatic Resources (BFAR) entering deep within the shoal to deliver supplies, apparently uncontested.

But in the spring of 2022, groups of four to five militia vessels began to consistently maintain a presence at Second Thomas and assist with CCG efforts to stop Philippine government ships from entering the shoal. At the same time, the Philippines shifted to using Philippine Coast Guard (PCG) ships to escort resupply missions, rather than the less capable BFAR vessels.

Later in the fall of 2022, the Philippines ran at least three resupply missions without any escorts for the small civilian transport boats. The head of the Philippines’ Western Command (WESCOM), Vice Admiral Alberto Carlos, said this was a deliberate choice and part of “trust-building efforts” being taken to exhaust “all available means of peacefully coexisting.”

In early 2023, however, the PCG began again escorting resupply missions. And in the second half of 2023, both Chinese and Philippine naval ships began to be seen regularly in the vicinity of Second Thomas during resupply missions. People’s Liberation Army-Navy (PLAN) vessels were observed nearby during five of the eight resupply missions observed since June 2023, with Philippine Navy ships in the area during three. (Note: Because PLAN vessels are rarely observed broadcasting AIS, their actual presence in 2021 and 2022 may have been more frequent than the data suggests.) And while not sending surface vessels, the U.S. Navy has provided the Philippines with an “eye in the sky” by deploying P-8 Poseidon maritime reconnaissance aircraft to Second Thomas during at least three of the last six resupply missions.

3. The Philippines has more consistently reported resupply missions and associated incidents with China over time, with a significant change in February 2023.

Fewer than half of observed resupply missions in 2021 (three of seven) were reported publicly by the Philippine government or media. In contrast, 80 percent (12 of 15) of observed resupply missions in 2023 were reported publicly, often on the same day the mission was conducted and/or a confrontation with Chinese vessels occurred.

This evolution toward the Philippines’ current level of transparency and active reporting about events at Second Thomas developed during 2022 and into early 2023. After previously only reporting missions in which a major incident occurred, the Philippines began experimenting with a more open approach in June of 2022 (before the current Marcos administration took office), when it invited journalists to join a rotation and resupply mission. It then publicly reported on all observed resupply missions for the second half of 2022.

But key details of those missions appear to have been left out of public releases at the time. For instance, WESCOM reported in August 2022 that a resupply mission had been conducted smoothly, “without any untoward incident.” It wasn’t until February 2023 that the PCG, then protesting the lasing of one of its ship by the CCG, revealed that during that August mission, a CCG vessel had removed the cover from one of its 70mm naval guns while forming a blockade with other CCG and militia ships, preventing the PCG from approaching the shoal.

February 2023 marked the beginning of the current era of “radical transparency” that has characterized messaging from the Philippines around Second Thomas Shoal ever since, with the PCG issuing statements and photos immediately after resupply missions are conducted, with or without major incident.

This increased level of transparency likely also contributed to a higher number of resupply missions being observed: 15 resupply missions were observed in 2023, as compared with 8 in 2022 and only 7 in 2021. But without more complete reporting from earlier years, it is impossible to discern whether this increase is entirely a product of better reporting, or if the Philippines has increased the tempo of resupply missions.

4. Major incidents were rare—until the second half of 2023

From 2021 through July 2023, while tensions at Second Thomas played out through aggressive maneuvering of ships and stern radio messaging, physical contact between Philippine and Chinese vessels appears to have been rare. After water cannons were used by the CCG against a Philippine supply ship in November 2021, the next publicly reported incident where physical contact was made was in August 2023, when water cannons were again used, this time against both the PCG and a supply ship.

Since then, physical encounters between Philippine and Chinese ships have increased at an alarming rate, with collisions and or Chinese use of water cannons against Philippine ships occurring in all three supply missions since October. December 10 was particularly tense, as water cannons disabled the engines of one Philippine supply ship while a CCG vessel collided with the other supply ship where the chief of staff of the Armed Forces of the Philippines was on board.

The Road Ahead

The Philippines has yet to conduct a seaborne resupply mission in 2024, saying that a mission planned for the weekend of January 20-21 was postponed due to damage to the Unaizah Mae 1, a civilian transport used to deliver supplies to the BRP Sierra Madre. Instead, food supplies were reportedly air-dropped as a stop-gap measure until regular missions can be resumed.

If collisions and the firing of water cannons persist as regular occurrences at Second Thomas, it may only be a matter of time before they trigger an accidental escalation by causing an unintended level of damage or loss of life. Perhaps aware of this risk, Philippine and Chinese officials on January 17 pledged to improve communications and resolve incidents through diplomacy after a bilateral meeting on South China Sea issues. But with the Philippines determined to both resupply and upgrade the Sierra Madre, these commitments are likely to have little impact unless accompanied by a change in CCG and militia tactics around the shoal.