Clashes in the South China Sea: Escalation at Second Thomas Shoal

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Over recent months, the frequency and seriousness of interactions between PRC Coast Guard and maritime militia forces, and Philippines Coast Guard and Armed Forces units in the vicinity of Second Thomas Shoal has escalated significantly. 17 June 2024 saw an incident involving China Coast Guard (CCG) small craft blocking in and surrounding Philippine Coast Guard (PCG) small craft. The PCG craft was engaged in one of the Philippines’ monthly attempts to resupply its outpost on the Shoal (discussed below). The incident involved CCG personnel brandishing bladed weapons and pointed tools, and striking at the PCG craft – many of which were visibly rigid hull inflatable boats (RHIBs) which can be holed (albeit with difficulty) by human wielded sharp weapons. There are reports that a PCG seaboat was indeed punctured, and also some reports that CCG seaboats forcibly tried to ‘impound’ or tow a PCG seaboat, and seized weapons from the PCG seaboats. It is reported that one Philippines Navy officer lost a thumb in the incident.

Kinetic operations have long been a feature of CCG – PCG interactions in the vicinity of Second Thomas Shoal, but until now have primarily been ship to ship – featuring the use of water cannons, shouldering, and ramming. This most recent incident, however, is much more visceral in that it involved CCG and PCG officers in direct contact, including the use of personal weapons and seizure of government property (prima facie entitled to sovereign immunity). One Senior Philippine official described it as ‘piracy’, but this can only be a colloquial use of the term. Under the UN Convention on the Law of the Sea (UNCLOS) vessels on government service cannot commit piracy unless they are under the control of a mutinied crew (see Article 102). That is not the case here; but the general point that this is a clearly escalatory step in the long simmering standoff at Second Thomas Shoal cannot be denied. Indeed, as the Philippines President recently indicated, escalation becomes much more serious where human life and injury are involved: ‘If a Filipino citizen is killed by a wilful act, that is, I think, very, very close to what we define as an act of war’. Indeed, a number of states, including Australia, took the quite dramatic step of informing the Chinese Government that their conduct in this incident had been ‘illegal’, as opposed to the heretofore more common labels employed when registering concern at dangerous CCG and PLA-N (and PLA-AF) conduct at sea, such as ‘unprofessional’ and ‘unsafe’.

In the remainder of this post we first outline why Second Thomas Shoal has become such a flashpoint. We then consider the implications of such incidents for the law on the use of force and (collective) self-defence under the UN Charter. Finally, we conclude with some consideration of questions of sovereign immunity and military activities at sea.

What is Second Thomas Shoal and why is it a flashpoint?

Second Thomas Shoal is a submerged feature surrounding a lagoon and provides an important fishing ground for Filipino fishermen. It is located ‘104.0 nautical miles from the archipelagic baseline of the Philippine island of Palawan and 616.2 nautical miles from China’s baseline point 39’ (South China Sea Award, para 290). It becomes an annual flashpoint in part because it falls within the ‘nine-dash line’ area of the South China Sea within which China claims jurisdiction and proclaims an annual fishing moratorium that runs from May to September.

The arbitral tribunal in the South China Sea case concluded that, at best, there may be some outcrops on the Shoal that are exposed at high tide. It is otherwise a completely submerged feature. This means it is a ‘low tide elevation’ (LTE) and not a rock or island under Article 121 UNCLOS capable of generating maritime zones (para 381). As such, LTEs are not capable of sovereign appropriation and form part of any Exclusive Economic Zone (EEZ) in which they are present. This means that the state with jurisdiction over the Second Thomas Shoal can only be the Philippines (paras 646-647). The Philippines has attempted to secure its control of the Shoal through the creation of a manned outpost in the form of the Philippines Naval vessel Sierra Madre, grounded there in 1997. While in increasingly dilapidated condition, it has nonetheless permitted a small continuous presence by the Armed Forces of the Philippines, albeit in very poor living conditions and in need of periodic relief and monthly external resupply.

China has continued to assert its claims to sovereignty over the waters surrounding the Second Thomas Shoal, principally through assertions of law enforcement jurisdiction. China’s controversial CCG Law 2021 permits the use of force and towing against ‘foreign organizations and individuals that infringe on China’s sovereign rights and jurisdiction at sea’, including sovereign immune foreign government vessels, throughout ‘maritime areas under China’s jurisdiction’. (The latter phrase creates deliberate uncertainty, as it is an ambiguous term not grounded in UNCLOS concepts such as the EEZ). As of 15 June 2024, CCG Regulation No. 3 permits the CCG to detain foreign vessels and persons in ‘waters under China’s jurisdiction’ for up to 60 days. The Philippines’ response to incidents in which the CCG has used force against Philippines-flagged fishing and government vessels had largely been one of naming and shaming: releasing dramatic footage of Chinese behaviour to news services and on social media in a highly effective information campaign. In 2023 this appeared to lead to a degree of CCG restraint, albeit that now seems to be breaking down.

A particular source of tension has been the fate of the Sierra Madre. ‘Chinese officials have accused Philippines supply ships of bringing construction materials to reinforce the vessel, violating an apparent earlier agreement, made by former President Rodrigo Duterte, that only basic supplies would be delivered to the marines stationed there.’ Thus recent clashes off the Second Thomas Shoal involved the CCG preventing ‘Filipino personnel from transferring supplies including food, fuel, M4 rifles, and navigation equipment.’

What does this mean for the UN Charter law on the use of force and collective self-defence?

The incidents under discussion obviously involve, in common parlance, the use of force by CCG officers against PCG officers. But do they constitute a prohibited use of force or an armed attack under the UN Charter? And if the answer to either question is yes, what are the implications for the US – Philippines Mutual Defence Treaty?

While Article 2(4) of the UN Chater prohibits the ‘the threat or use of force’ in international relations, it is commonly suggested that ‘police action’ levels of force do not violate this prohibition as mere police actions do not threaten the territorial integrity or political independence of another state. As a general proposition, it is hard to see how this argument follows, policing powers and the monopoly on violence being a core attribute of sovereignty. That said, where the law of the sea positively authorises law enforcement action, then reasonable and proportionate uses of force by government vessels against foreign-flagged merchant or fishing vessels are obviously unobjectionable (the classic case being MV Saiga (No 2)). Regardless, such an argument cannot benefit China. First, there would need to be some valid claim to law enforcement jurisdiction. Second Thomas Shoal is a LTE generating no maritime zones and is present in the Philippines’ EEZ. Any claim to law enforcement jurisdiction in the vicinity must therefore belong to the Philippines. Second, hypothetically, even if there were some nearby rock belonging to China and generating a territorial sea, a Philippines vessel on governmental non-commercial service plainly enjoys sovereign immunity and may not be subjected to law enforcement action (on which, more below). Further, it was held (somewhat controversially) in Guyana v Suriname that a mere threat of unspecified ‘consequences’ made by a government vessel could violate the prohibition on the threat of force when made in defence of sovereign claims to resource jurisdiction. On this basis it is hard to reach a conclusion other than that China’s acts involve an illegal use of force. Does this trigger a right to self-defence?

Under Article 51 of the UN Charter a right to self defence arises if ‘an armed attack’ occurs. It is uncontroversial that an attack on a State’s public vessel – or even a merchant vessel flagged to the State – may be equated to an attack on the State itself for the purposes of self-defence. (This privileged position of flagged merchant vessels is a peculiarity of the law of the sea.) However, in ICJ case law an ‘armed attack’ must be of sufficient ‘scale and effects’ that it cannot be classed as a ‘mere frontier incident’ (Nicaragua v US, para 195). The recent episode at Second Thomas Shoal, featuring bladed personal weapons short of firearms, seems more like a frontier incident than an armed attack. This would appear, then, not to give rise to a right of self-defence or collective self-defence. The US, however, ‘has long maintained that a State can use force in self-defense in response to any amount of force by another State’. This would seem to suggest that the United States–Philippines Mutual Defense Treaty could be implicated by such an episode, at least from a US standpoint. The treaty, however, does not provide automatically that ‘an armed attack against one’ is ‘an armed attack against … all’ in the manner of Article 5 of the North Atlantic Treaty. Rather the key obligation in Article 3 is that the parties ‘will consult … whenever in the opinion of either of them the territorial integrity, political independence or security of either … is threatened by external armed attack’.

Related UNCLOS implications?

There are numerous UNCLOS-related issues that arise from this incident; however, there are three specific issues related to the use of force (in the broad sense) that merit analysis here. The first is the clear breach of UNCLOS and general international law provisions on seizing sovereign immune vessels (the seaboats) and government property (things from the seaboats). However, the legal source for the sovereign immunity claim in respect of (on one hand) the vessels and (on the other hand) the things in the vessels, may differ. This is because while UNCLOS specifically refers to sovereign immune vessels (Articles 42(5) and 236, for example), the immunities from seizure at sea in respect of other government assets, and indeed government officials, is likely found in general international law rather than UNCLOS. This recent Second Thomas Shoal incident is a case of UNCLOS rules both relying on and being supplemented by general rules of international law. First, UNCLOS both states rules of immunity (eg Articles 95 and 96) and also refers to concepts of ‘sovereign immune’ vessels plainly found outside UNCLOS. Second, to the extent that objects belonging to a government vessel or crew enjoy immunity from arrest or seizure, they do so as a consequence of general rules of international law on the immunity of states and their property.

The second, and closely related issue is the nature of the action taken against the Philippine seaboats: specifically, temporary detention. This is a clear breach of vessel sovereign immunity regardless of the purported zone in which it occurs. There is a long history of incidents and cases that affirm the fundamental rule that, outside of armed conflict, sovereign immune vessels cannot be subjected to the jurisdiction of any other state. When North Korean forces seized the USS Pueblo in early 1968, the seizure of the vessel (still in North Korean hands) and the 11 month detention of the crew were clearly unlawful and a breach of sovereign immunity. This was regardless of allegations that it was an intelligence gathering warship that had entered to the North Korean territorial sea. The same issue arose in the 2007 HMS Cornwall incident, where two Royal Navy seaboats and fifteen Royal Navy and Royal Marines personnel were detained by the Iranian Islamic Revolutionary Guard Corps Navy in the North Arabian Gulf. This immunity from the jurisdiction of all other states applies across all maritime zones, including internal waters, as ITLOS reiterated in the ARA Libertad case.

The third clear and immediate implication is that it will perhaps crystalise – for discussion purposes if not for any dispute resolution mechanism – the uncertainty currently attending the definition of ‘military activities’ in UNCLOS Article 298. In one respect, this is a narrow issue. The concept performs a specific task in Art 298(1)(b) in terms of excluding certain disputes form the aegis of compulsory UNCLOS Part XV dispute resolution processes. However, as a law of the sea informed concept with an important disciplining and descriptive function beyond these formal mechanisms, ‘military activities’ has a life beyond Article 298. The challenge is that in two recent decisions – the 2016 South China Sea Arbitral Award (SCS Award), and the 2019 ITLOS Ukraine v Russia Provisional Measures Order of 15 May 2019 (Kerch Strait Provisional Measures), described in more detail below – it has been interpreted in radically different (even opposed) ways (for commentary, see here and here, for example). This has created uncertainty rather than refinement or clarity.

This is because, on one hand, this particular Second Thomas Shoal incident would clearly meet the approach to ‘military activities’ adopted in the SCS Award (para 1161) – where the fact nexus was in fact prior second Thomas Shoal incidents:

In connection with this stand-off, Chinese Government vessels have attempted to prevent the resupply and rotation of the Philippine troops on at least two occasions. Although, as far as the Tribunal is aware, these vessels were not military vessels, China’s military vessels have been reported to have been in the vicinity. In the Tribunal’s view, this represents a quintessentially military situation, involving the military forces of one side and a combination of military and paramilitary forces on the other, arrayed in opposition to one another. As these facts fall well within the exception, the Tribunal does not consider it necessary to explore the outer bounds of what would or would not constitute military activities for the purposes of Article 298(1)(b).

However, the ITLOS Kerch Strait Provisional Measures Order approach to ‘military activities is fundamentally different. ITLOS (at paras 63-77) leveraged three arguments to determine that the incident was a law enforcement situation not a military activity:

In the view of the Tribunal, it is difficult to state in general that the passage of naval ships per se amounts to a military activity. Under the Convention, passage regimes, such as innocent or transit passage, apply to all ships (para 68).

[T]he core of the dispute was the Parties’ differing interpretation of the regime of passage through the Kerch Strait. In the view of the Tribunal, such a dispute is not military in nature (para 72).

[T]he … sequence of events … appears to be the use of force in the context of a law enforcement operation rather than a military operation (para 74).

Consequently, if adopting a similar ‘law enforcement’ shading to this recent Second Thomas Shoal incident was prioritised, it would likely fall outside the scope of ‘military activities’. In this regard, this escalatory Second Thomas Shoal incident raises the clear prospect that an interpretive approach previously specifically found to apply to that same location, actors, and context could be displaced by the more recent but much narrower ITLOS Kerch Strait Provisional Measures interpretive approach (which was, in many respects, adopted so as to enable jurisdiction rather than to better define or clarify the underpinning concept). As a contextual definition, the SCS Award is to be preferred; as a means of creating formal dispute resolution mechanism jurisdiction in support of a wronged state, the ITLOS approach is to be preferred. Perhaps discussions around this most recent incident might assist in determining which conception is to take precedence, with the point of distinction from the Kerch Strait Provisional Measures approach being the arguable illegitimacy of the underlying Chinese claim to jurisdiction, and thus of any law enforcement characterisation.


Not long prior to this escalatory Second Thomas Shoal incident, the Philippines’ President had identified a new political red line – essentially, that any CCG killing of a PCG or AFP member during such interactions at sea would be ‘close to… an act of war’. This political red line is not exactly concurrent with the Article 51 self-defence threshold, on most interpretations, although the killing of a state agent does perhaps bring it closer. In other respects, this political red line is already well beyond other relevant legal thresholds – such as interference with sovereign immunity – and may also inform the UNCLOS ‘military activities’ debate, perhaps returning the pendulum towards the more contextual approach of the SCS Arbitral Award as opposed to the jurisdictional prioritisation evident in the ITLOS Order. And then, as directly invoked by the President’s statement, there is the issue of the threshold for an International Armed Conflict as per common article 2 of the Geneva conventions. But that is a discussion for another day…

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Valentin Schatz says

July 11, 2024

Dear Douglas and Rob,

thank you for an enjoyable post! I believe the Enrica Lexie award supports your views on sovereign immunity of government personnel.

On "military activities" I would have been interested in your views not only of SCSA and ITLOS Ukraine v. Russia, but also of the 'compromise' approach in the award on preliminary objections of the Annex VII arbitral tribunal in Ukraine v. Russia (

Best regards


Melissa Loja says

July 12, 2024

Why use a fake photo?

Marko Milanovic says

July 12, 2024

Dear Melissa,

The photos we use at the beginning of the article are stock photos corresponding to the overall theme (e.g. the law of the sea). This is the case with most posts we publish. There is no implication that the photo we used has anything directly to do with the incident being discussed - it's just visual splash.


Melissa Loja says

July 12, 2024

Thanks for the clarification. The photo is of a swarm of fishing boats in West Lamma Channel off the coast of Hong Kong.