The Ayungin Withdrawal: a Second Thomas Shoal clash that the United States chose not to widen

Summary

This scenario starts in the place where US and Chinese forces have come closest to direct contact in recent years: Second Thomas Shoal (Ayungin to Manila, Ren'ai Jiao to Beijing) in the Spratly Islands. Since 1999 a small Philippine Marine detachment has lived aboard the grounded, rusting BRP Sierra Madre. Its supply runs have met steadily more physical pressure from China: water cannon and collisions in 2023, an armed boarding in June 2024, and further near-collisions as recently as September 2026 [6][7][10].

The trigger is a resupply mission that goes wrong. A China Coast Guard (CCG) boarding turns into gunfire, Filipino personnel are killed, and Manila formally invokes Article IV of the 1951 Mutual Defense Treaty (MDT). Washington has said many times that the treaty covers Philippine armed forces, public vessels and aircraft, coast guard included, "anywhere in the South China Sea" [8][5]. It therefore sends a destroyer-escorted resupply convoy. China fires first in the military phase. After a further confrontation, PLA forces hit the escorting US surface group with anti-ship ballistic and cruise missiles launched from the mainland and from the Spratly bases. Within about 36 hours two US destroyers are sunk and a third is badly damaged, with some 450-600 US sailors killed.

The President then faces a choice: strike Chinese bases (including on the mainland) and risk a general war, or stop. He stops. A ceasefire brokered through ASEAN channels leaves China controlling access to the shoal. The Sierra Madre garrison is evacuated under a face-saving "humanitarian" arrangement.

The fighting lasts about four days, and the crisis about three weeks. China wins without taking territory by force. It establishes de facto control over the waters inside the "nine-dash line" near the Philippines, and it shows Tokyo, Canberra, Seoul and Taipei that a US treaty commitment can be priced out. Published research judges this path unlikely, because both capitals have strong incentives to keep the fight from starting. It depends on several assumptions, set out below.

At a glance

Background and assumptions

The setting. Second Thomas Shoal lies inside the Philippine exclusive economic zone; the 2016 arbitral award, which Beijing rejects, found that China cannot assert maritime claims against the Philippines in such areas [5]. The Sierra Madre is still a commissioned Philippine Navy ship. That status matters, because it makes an attack on it an attack on Philippine "armed forces" or "public vessels" for MDT purposes. CSIS's Asia Maritime Transparency Initiative found that the average number of Chinese vessels present during Philippine resupply missions rose from about one in 2021 to about 14 in 2023, peaking at 46 on 10 December 2023. After a lull following a November 2021 water-cannon incident, physical contact resumed in August 2023 [6]. On 17 June 2024 CCG personnel carrying bladed weapons boarded Philippine Navy boats, seized seven rifles and injured eight Filipinos, one of whom lost a thumb [7]. A "provisional arrangement" in July 2024 calmed things for a while [9]. The two sides never published an agreed text, however, and by September 2026 each was accusing the other of breaking it after a new confrontation [10].

The US commitment. In 2021 the Secretary of State said an armed attack on Philippine forces, public vessels or aircraft in the South China Sea "would invoke" Article IV [8]. Later statements explicitly added the coast guard [5]. Article IV itself only commits each party to "act to meet the common dangers in accordance with its constitutional processes" (treaty text). The wording does not automatically require any particular military response. That gap is what this scenario exploits.

The military balance. The 2024 DoD China Military Power Report counts more than 370 PLA Navy ships and submarines, rising to about 395 by 2025. It lists five anti-ship ballistic missile types: the DF-21D, DF-26, DF-17, DF-27 and YJ-21 [4]. Among them the DF-21D, DF-26 and YJ-21 are the most relevant here. Second Thomas Shoal is close to China's fortified artificial island at Mischief Reef and well within range of mainland-based missiles. CSIS's Taiwan wargames found that US surface ships operating inside this missile umbrella suffer heavy losses. Across 24 iterations the US typically lost two carriers and 10-20 large surface combatants [1][2]. US stocks of long-range precision munitions could run short in under a week of high-intensity war [3].

What must be true for this path.

1. China decides a lethal incident is acceptable, or a local commander lets one happen. China has so far deliberately stayed below the "armed attack" threshold, using water cannon and blades rather than firearms [7].
2. Washington answers with a visible but limited naval escort rather than with air power or by reinforcing the Philippines' own forces. The escort puts US ships within China's missile range without a plan for escalation dominance.
3. Beijing judges that striking US warships, but not US bases or territory, keeps the war limited, and that Washington will not trade a wider war for an uninhabited reef.
4. The US President, facing low public appetite, depleted munitions [3] and a possible Taiwan contingency, decides that the risk of escalating is greater than the cost to credibility.

Likelihood. Most published analysis treats deliberate Chinese lethal force at the shoal as unlikely. Gray-zone tactics exist precisely to avoid triggering the MDT, and CRS describes Beijing's strategy as gradual, coercive control rather than open combat [5]. A sinking of US warships followed by a US withdrawal is less likely still. US doctrine and politics both lean toward retaliation after losing ships. Treat this scenario as a low-probability, high-consequence tail case. Its value is that it shows where commitment is weakest: an uninhabited feature, a treaty with no automatic response, and a US force deployed within range of a large missile arsenal.

Timeline

• D-180 — China declares stricter "law-enforcement" rules for Ren'ai Jiao and requires prior notification of all resupply runs. Manila rejects them as incompatible with the 2016 award, and the US State Department supports Manila [5][10].
• D-150 — The Philippine Defense Secretary repeats that no binding resupply arrangement with China exists, and the Chinese embassy accuses Manila of violating the 2024 understanding [10]. Both sides harden their public positions.
• D-120 — The US keeps its mid-range Typhon launcher on Luzon. Beijing repeats its demands, first made after the April 2024 deployment, that it be withdrawn [11]. In the scenario, China's MFA now links the system to the shoal dispute.
• D-90 — The CCG increases patrols, and about 40 maritime militia vessels gather around the shoal, similar to the peak AMTI recorded in December 2023 [6]. Manila begins planning reinforced, escorted resupply runs.
• D-60 — Philippine engineers try to bring welding equipment to shore up the Sierra Madre's hull. The CCG blocks them with water cannon, and two Philippine sailors are injured. The US ambassador condemns "escalatory tactics" [10].
• D-45 — PLA Southern Theater Command announces live-fire drills near the Spratlys. The US Navy moves a destroyer squadron into the Sulu Sea. Japan and Australia call for restraint.
• D-30 — US and Philippine officials confirm in private that the MDT would apply to an attack on the resupply boats. US public messaging stays ambiguous about what response would follow.
• D-14 — Philippine Western Command warns publicly that ramming and boarding, already seen in December 2023 and June 2024, will follow the water cannon, and says crews will resist boarding [14][7]. China's MFA warns of "consequences".
• D-1 — A Philippine resupply convoy (two contracted boats, two navy RHIBs, one coast guard cutter) departs Palawan. CCG cutters and militia boats take up blocking positions.
• D-day, 06:00 — CCG boarding teams try to seize the RHIBs. Philippine Marines resist. A CCG officer fires, Marines on the Sierra Madre fire back, and the CCG opens fire with deck guns. Six Filipinos and three Chinese personnel are killed. Each side says the other fired first.
• D-day, 14:00 — President of the Philippines formally requests consultations and assistance under MDT Articles III and IV. Beijing calls the incident a "grave provocation" in Chinese waters and places the shoal under a "temporary control zone".
• D-day, 20:00 — The US President announces that the US will "escort Philippine resupply missions" and calls the deaths an armed attack under the treaty. China raises PLA readiness in the Southern Theater.
• D+1 — Two US Arleigh Burke-class destroyers and a littoral combat ship, with Philippine frigates, form an escort group east of the shoal. P-8 patrol aircraft fly overhead. The PLAN sends a surface action group from Mischief Reef and the Paracels.
• D+1, evening — Beijing issues a public ultimatum: foreign warships entering the "control zone" will be "dealt with resolutely." Washington says it will proceed. Tokyo quietly asks Washington to avoid strikes from Japanese bases.
• D+2, 05:00 — The escort group moves toward the shoal, and a CCG cutter crosses the bow of the US lead destroyer. A Chinese helicopter is shot down after an aggressive approach. Accounts conflict over whether it fired a missile first.
• D+2, 07:30 — The PLA fires a salvo of anti-ship ballistic and cruise missiles (DF-21D/YJ-series types in the 2024 CMPR inventory [4]) at the escort group, from the mainland and from Spratly-based launchers. The destroyers' air defences intercept most of them but are saturated. One destroyer sinks.
• D+2, 09:00 — US aircraft from Okinawa and a carrier in the Philippine Sea strike the PLAN ships that fired and sink one Type 056 corvette. The White House does not authorise strikes on Mischief Reef or the mainland.
• D+2, 16:00 — A second salvo sinks another destroyer and badly damages the LCS. Total US dead pass 450. US surviving forces withdraw east of Palawan.
• D+3 — China says it has "completed the defence of Ren'ai Jiao" and offers a ceasefire with "humanitarian evacuation" of the Marines. The Pentagon briefs that strikes on Mischief Reef would probably bring mainland strikes on Luzon and Guam. Munitions planners warn of shortages [3].
• D+3, evening — The National Security Council debates. The Chairman advises that escalation can be won but only with losses well beyond those of the CSIS Taiwan games [1][2], and that the US would be exposed if Taiwan is then threatened. The President opts for a ceasefire.
• D+4 — The US accepts a ceasefire, conveyed through Indonesia and Malaysia, and frames it as "preventing a wider war." Manila protests but has no independent means to break the cordon.
• D+5 — Congress is divided. Some members call for retaliation; others question whether the MDT covers an uninhabited reef. Polls show majorities against widening the war, despite the pre-war support for defending allies measured in 2024 [13].
• D+7 — The Sierra Madre's 12 Marines are evacuated by a Philippine Coast Guard cutter, which the CCG "verifies". China places buoys and a coast guard station ship at the shoal.
• D+10 — Marcos's successor-in-waiting and opposition figures call for a review of EDCA access. Analysts recall Lowy's warning that politics on both sides is too unpredictable for any access arrangement to be secure [12].
• D+14 — Japan's cabinet commissions an urgent review of its alliance with the United States. Australia reaffirms ANZUS but calls for "clarity" in US commitments.
• D+18 — Talks between the ASEAN Chair, China and the Philippines produce a "joint understanding": Philippine fishing access in exchange for no Philippine military presence at the shoal. Washington welcomes it.
• D+21 — Taiwan's legislature debates whether US assurances are credible. The PLA starts large-scale exercises around Taiwan without attacking it.
• D+60 — The Philippines suspends some EDCA site expansion and the Typhon is removed [11]. China begins dredging near the shoal. The US re-states the MDT with new conditions.
• D+180 — Vietnam and Malaysia quietly reach bilateral "arrangements" with China over their Spratly outposts. South Korea and Japan increase their own defence spending and openly debate nuclear options.

World politics and allies

Philippines. Manila is the main loser. The alliance was revived under Marcos after being "on life support" under Duterte, and Lowy warns that politics on both sides makes access arrangements fragile [12]. After the US withdrawal, Philippine politics swings toward accommodation, much as it did in the Duterte era. Manila does not abandon the MDT, but it shrinks EDCA activity and the Typhon deployment [11][12].

Japan. Tokyo draws the sharpest lesson. A US unwillingness to fight for a Philippine reef raises the question of what Washington would do over the Senkakus. Expect Japan to strengthen its own counterstrike capability, demand written assurances, and hedge diplomatically with Beijing.

Australia. Canberra reaffirms ANZUS and AUKUS, but its defence debate moves toward self-reliance and away from forward deployment in the South China Sea.

South Korea. Seoul ties the episode to doubts about US extended deterrence on the Korean Peninsula, and calls for an independent nuclear option grow.

Taiwan. Taipei is the audience China cares most about. US credibility suffers, but a determined Taiwan would also learn that the US may not engage within PLA missile range without long preparation.

NATO/EU. European governments call for de-escalation. The episode deepens European worry that the US is overstretched, and pressure to build European capacity grows.

India. New Delhi condemns the use of force, avoids taking sides, and quietly accelerates maritime cooperation with Vietnam and the Philippines.

Russia, North Korea, Iran. Moscow backs China at the UN and calls the escort "provocative". Pyongyang treats the episode as proof that US alliances are unreliable. Tehran uses it as propaganda. None gives China material help, and none is needed.

Global South and ASEAN. ASEAN members are split. Indonesia and Malaysia gain prestige as mediators. Vietnam is alarmed. Many Global South states see the outcome as evidence of a shifting balance of power.

UN. A Security Council resolution is blocked by Chinese and Russian vetoes. The General Assembly passes a non-binding call for restraint. China invokes its rejection of the 2016 award [5].

How China wins

China's victory is not territorial conquest. It is a negotiated settlement on Chinese terms combined with a lasting shift in perceptions. In practice:

1. De facto control of Second Thomas Shoal. The last Philippine outpost inside China's claimed zone near Mischief Reef is gone, and nothing remains to physically challenge China's administrative control [6].
2. The MDT is shown to have limits. The US did act, but the scale of its response was set by Beijing's willingness to absorb risk and Washington's unwillingness to strike Chinese territory. Article IV's "constitutional processes" wording proves elastic [8].
3. Allied hedging. Japan, the Philippines, Vietnam and others adjust their policies, which reduces US access and forward posture in the First Island Chain.

Why the US accepts it. Several reasons converge. The stake is an uninhabited reef. Retaliating against Mischief Reef or mainland launchers would very likely lead to strikes on US bases and a war resembling the CSIS Taiwan games, which cost thousands of US lives and multiple carriers [1][2]. Munitions shortages would set in within days [3]. US public opinion largely supports using troops to defend allies [13], but in this scenario support collapses once the cost of a war with China becomes concrete. And Washington would want to keep its forces intact for a possible Taiwan contingency. The President can present the ceasefire as preventing a world war, and much of the US electorate would accept that framing. Allies would not.

Losses

These figures are illustrative assumptions for this scenario, not modelled outputs. No published open-source wargame models this exact clash.

What would change the outcome

1. A clear, pre-declared US response. If Washington had stated in advance that it would strike the forces responsible for any attack, including those on Spratly bases, Beijing's calculation in assumption 3 would change. Ambiguity in Article IV invites probing [8].
2. Stand-off escort rather than a surface convoy. Supporting resupply with air cover, uncrewed systems and Philippine assets, instead of sending US destroyers within PLA missile range, would reduce exposure to the CSIS-type losses [1][2].
3. Munitions depth. Larger stocks of long-range anti-ship and air-defence munitions would weaken the argument that the US cannot sustain a limited exchange [3].
4. Allied burden-sharing in advance. A Japanese and Australian commitment to joint presence would raise China's risk and reduce the impression that the US stands alone.
5. Diplomatic off-ramp before shooting. A published, verifiable resupply arrangement would remove the trigger. The 2024 understanding failed because its text was never agreed in public [10].

References

1. Mark F. Cancian, Matthew Cancian, Eric Heginbotham, The First Battle of the Next War: Wargaming a Chinese Invasion of Taiwan, CSIS, 9 January 2023. https://www.csis.org/analysis/first-battle-next-war-wargaming-chinese-invasion-taiwan
2. Taiwan News, "US would lose 2 aircraft carriers, 3,200 troops in Chinese invasion of Taiwan: CSIS" (summary of CSIS loss figures), January 2023. https://www.taiwannews.com.tw/en/news/4775256
3. Seth G. Jones, Empty Bins in a Wartime Environment: The Challenge to the U.S. Defense Industrial Base, CSIS, 23 January 2023. https://www.csis.org/analysis/empty-bins-wartime-environment-challenge-us-defense-industrial-base
4. US Department of Defense, Military and Security Developments Involving the People's Republic of China 2024 (fact sheet as reproduced by Andrew S. Erickson), December 2024. https://www.andrewerickson.com/2024/12/department-of-defense-just-released-2024-china-military-power-report-fact-sheet-full-text-here/
5. Ronald O'Rourke, U.S.-China Strategic Competition in South and East China Seas: Background and Issues for Congress, Congressional Research Service R42784, updated 1 May 2025. https://www.everycrsreport.com/reports/R42784.html
6. CSIS Asia Maritime Transparency Initiative, "Tracking Tensions at Second Thomas Shoal", 30 January 2024. https://amti.csis.org/tracking-tensions-at-second-thomas-shoal/
7. BenarNews, "Philippines demands return of firearms confiscated by Chinese during sea encounter", 19 June 2024. https://www.benarnews.org/english/news/philippine/south-china-sea-06192024123658.html
8. gCaptain / Bloomberg, "Blinken Says A South China Sea Attack Would Trigger War Treaty", 12 July 2021. https://gcaptain.com/south-china-sea-war-treaty/
9. Manila Times, "PH, China reach arrangement on resupply mission", 21 July 2024. https://manilatimes.net/2024/07/21/news/ph-china-reach-arrangement-on-resupply-mission/1958876
10. Daily Tribune (Philippines), "Stop fanning flames, Chinese embassy tells US after siding with PH amid recent confrontation in Ayungin Shoal", 27 September 2026. https://tribune.net.ph/2026/09/27/stop-fanning-flames-chinese-embassy-tells-us-after-siding-with-phl-amid-recent-confrontation-in-ayungin-shoal
11. Arab News / Reuters, "US keeps missile system in Philippines as China tensions rise, tests wartime deployment", 19 September 2024. https://www.arabnews.com/node/2571962/amp
12. Susannah Patton, "Making the US-Philippine alliance count", Lowy Institute (first in War on the Rocks), 15 June 2023. https://www.lowyinstitute.org/publications/making-us-philippine-alliance-count
13. Chicago Council on Global Affairs, 2024 Survey of American Public Opinion on U.S. Foreign Policy, 2024. https://globalaffairs.org/research/public-opinion-survey/2024-survey-public-opinion-us-foreign-policy
14. BenarNews / RFA, "Philippines, China accuse each other of ship ramming", 10 December 2023. https://www.benarnews.org/english/news/philippine/southchinasea-ramming-12102023091909.html

← Fait Accompli: A Short-Warning Invasion of Taiwan The Long War: Attrition, Empty Bins and a Negotiated Settlement →