BRP Sierra Madre: The Waves of Uncertainty Surrounding the Sentry of the Second Thomas Shoal

Bryan Kerr Marco
The BRP Sierra Madre, a WWII-era LST-542-class landing ship, acting as an outpost on the Second Thomas Shoal. Source: US Naval Institute

The Second Thomas Shoal (China: Ren’ai Jiao; The Philippines: Ayungin Shoal) is an island in the Spratly Islands (China: Nansha Qundao; The Philippines: Kalayaan Islands) located in the South China Sea, one of the world’s most contentious areas. Since 2023, the number of maritime confrontations between the shoal’s claimants has increased. China’s 9-Dash Line claims it uses historical maps and records. Nonetheless, it is part of the Philippines’ EEZ, as recognized by international law. However, this discussion will not focus on who owns it, but on explaining why it recently became important. Wherein at its center is a derelict shipwreck that has turned into the regional dispute’s geopolitical flashpoint.

A Sentry’s Burden

Map showing the Dangerous Ground (blue-dashed lines) and the secret US sea lanes used for their nuclear submarines during the Cold War (red-dashed lines). Source: AMTI

The Second Thomas Shoal serves as a vital gateway for both claimants in the Spratly Islands. This is because of the shoal’s location on the Dangerous Ground, an area of the Spratly Islands with shallow depths that has always been poorly chartered. Sailing directions for the Second Thomas Shoal state that it is only accessible to ships with at least medium drafts. Until recently, in 2020, sailing instructions advised to avoid the area for all mariners’ safety due to the lack of accurate data. However, covert hydrographic studies conducted by maritime powers in the 1930s demonstrated that understanding the area’s internal sea lanes is critical for strategy.

There are only so many sea lanes to sail between the shallows, which essentially creates chokepoints. These lanes are easily blockaded, making it easier for China to disrupt Philippine resupply efforts. Philippine officials believe China wants to build a military base on the shoal since it is a suitable location. As Philippine officials have noted, the BRP Sierra Madre serves as an outpost to monitor not only the Chinese-occupied Mischief Reef but also the adjacent sea lanes.

Map showing Reed Bank situated east of the Spratly Islands and west of Palawan, Philippines. Source: BusinessWorld

Similarly, the Philippines’ possession of the shoal is an important access point to its westernmost territories in the Spratly Islands. Alternatively, it serves as an obstacle to China seizing the strategically significant Reed Bank (Philippines: Recto Bank) Wherein around one-fifth of the area’s 12 billion barrels of oil and 160 trillion cubic feet of natural gas are thought to be beneath Reed Bank. This will be a significant economic gain for China, but it is a necessity to the Philippines to solve its energy crisis.

Malampaya, the Philippines’ only gas field, is estimated to run dry by 2027. In effect, it will decrease power supply in the main island of Luzon by 40%, leading to severe outages. In addition, the alternative of importing liquefied natural gas will significantly raise energy prices nationwide. In these aforesaid contexts, for the Philippines, the BRP Sierra Madre is burdened with the responsibility as its sole stronghold in the disputed region.

A Deadly Game of Patintero

With the strategical importance of the shoal explained, it is also important to know how this affects the way the claimant parties act in the disputed region. Patintero is a traditional Filipino outdoor game wherein players race to the other side of a rectangular area without getting tagged. Inside the rectangle, taggers are situated at specific positions to prevent runners from passing through. Similarly, this is what is happening in and around the Second Thomas Shoal. Philippine vessels attempt to navigate through a Chinese blockade to reach the shoal. The former’s goal is to deliver supplies to the BRP Sierra Madre, a dilapidated WWII-era landing ship under the Philippine Navy.

Map showing the location of several closely-linked maritime features, which includes the Second Thomas Shoal and Mischief Reef. Source: Radio Free Asia

In 1995, Chinese forces took Mischief Reef (China: Meiji Jiao; The Philippines: Panganiban Reef), a small island a few kilometers northwest of the Second Thomas Shoal. Former Philippine Defense Secretary Orlando Mercado noted that the Philippine government was scrambling to devise a plan as a response. By 1999, they agreed that BRP Sierra Madre be run aground on the shoal to serve as an outpost. Later, Philippine journalist Marites Vitug coined the term “aground strategy” to refer to the Philippines’ policy to deploy obsolete warships to assert their sovereignty. 

The plan was successful, but subsequent attempts were carried out far too late, as China became prepared. Manila’s indecision and lack of conviction cost them a significant opportunity. Nonetheless, despite concerns, BRP Sierra Madre stayed, posing a dilemma for Beijing. Article 95 of UNCLOS grants a nation’s warships sovereign immunity from external interference. Essentially, the ship is an extension of the Philippines’ sovereignty. The principle of self-defense, as stated in Article 51 of the UN Charter, empowers a country to defend itself in the case of an attack, including its warships. Furthermore, the Philippines is protected by a Mutual Defense Treaty of 1951, which is a collective defense agreement signed with the United States.

In simple terms, if China decides to remove or board the vessel and detain its garrison, it will be considered an act of war against the Philippines. In turn, it would invoke the US to fulfill its defensive obligations under the MDT against China. The BRP Sierra Madre still being a commissioned warship under the Philippine Navy gives it a legal character based on international law. This not only stopped China from forcefully removing the ship, but it also prevented the seizure of the Second Thomas Shoal.

Philippine Coast Guard vessels BRP Cabra and BRP Sindangan swarmed by Chinese Coast Guard and Chinese Maritime Militia vessels during a resupply mission to BRP Sierra Madre. Source: Philippine Coast Guard via PhilStar

However, China has an ingenious strategy to overcome this obstacle. As seen with confrontations since 2012, it is common to see swarms of Chinese vessels surrounding an island, where they tend to overwhelm the outnumbered Philippine vessels sailing through the contested areas. PLA General Zhang Zhaozong coined this as the cabbage strategy, where they use a swarm of ships to form a blockade and seize an island. Essentially, it is to exhaust the Philippines with the pressure of keeping the BRP Sierra Madre supplied and force them to eventually concede.

With this strategy, China does not break any of the aforementioned laws, but it skirts around using gray-zone tactics to take advantage of loopholes. This is because they are not directly interfering with the ship and its garrison, but indirectly targeting them by cutting off the supplies. The result is a repetitive game of patintero that does not end until the runner, the Philippines, becomes exhausted and eventually concedes.

Risks Amid Uncertainty

2 Chinese Coast Guard vessels firing their water cannons on a Philippine resupply vessel, Unaiza May 4, heading towards BRP Sierra Madre, 4 people were injured. Source: Philippine Coast Guard via GMA Network

In the background of all the tension around the shoal is a power struggle between the United States and China, wherein several states are stuck in between. Experts are still divided on whether conflict is imminent in the Pacific. On the one hand, some feel that the growing rivalry between these two superpowers will make it more difficult to avoid a confrontation in the future. On the other hand, some claim that both nations are not eager to go to war because of the potential destruction.

However, what is common among these arguments is how they present the unnerving reality of uncertainty. Currently, all parties are aware of the dangers that may arise from the aforesaid deadly game of patintero at sea. For instance, ASEAN, although hesitant, still wants to maintain the status quo as it is essential to ensure the region’s stability.

What is seen are the effects of uncertainty in geopolitics, which experts believe stem from fear, confusion, ignorance, and indeterminacy. This uncertainty creates risks, as parties to the dispute will try to skirt around the limits to pursue their goals. One example would be China’s aforesaid policy of using its gray-zone tactics as part of its wager to achieve its goals over the Second Thomas Shoal. Even if these kinds of actions seem to steeply rock the stability of the region, these can be described as calculated risks in exchange for great rewards.

As a result, the question to ask amid heated maritime confrontations between the Philippines and China is not if a conflict would occur, but rather how they might avoid it. From the beginning of the dispute over the Second Thomas Shoal to the strategies used in context, what has been addressed can be defined as a risky dance at the edge of uncertainty. The BRP Sierra Madre, one of the first risky moves done in the South China Sea, has become the center point of conflict between the Philippines and China.

At this point, it is unknown whether China would be able to force the Philippines to concede the shoal. Nor can anyone determine today if a risky strategy fumbles into the spark that this dispute needs to open the gates of war. What is truly certain for now, is that the future of the decrepit BRP Sierra Madre and its beleaguered garrison is determined by which among the two nations are prepared to remain devoted and risk the most in the face of uncertainty.

Suggested Readings

Congressional Research Service. (2024). China-Philippines tensions in the South China Sea. Retrieved April 24, 2024, from

Council on Foreign Relations. (n.d.). China’s maritime disputes: 1897-2023. Retrieved April 24, 2024, from

Panda, A., & Putz, C. (2023). South China Sea flashpoints: The second Thomas Shoal crisis. The Diplomat. Retrieved April 24, 2024, from

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BRP Sierra Madre: The Wav…

by Bryan Kerr Marco time to read: 7 min