Attacks on Merchant Shipping: Which State Has the Right to Respond in Self-Defence?

On April 13, 2024, Iranian special forces seized the Portuguese flagged MSC Aries near the Strait of Hormuz as it sailed towards the Nhava Sheva port in India. The ship, which contained a predominantly Indian or Filipino crew, was chartered and operated by the Geneva-based Mediterranean Shipping Company. It was owned by Gortal Shipping, a company affiliated with the UK headquartered Zodiac Maritime, which is owned by the Monaco based Israeli billionaire Eyal Ofer. The list of States with potential links to the MSC Aries therefore includes Portugal, India, the Philippines, the United Kingdom, Switzerland, Monaco, and Israel. Could any of these States plausibly claim a right to act in self-defence pursuant to Iran’s actions?

Any analyses of a potential use of force against Iran pursuant to the right of self-defence would have to address the wider context surrounding Iran’s actions, as well as the question whether the seizure of the vessel constituted an armed attack. The aim of this post is not to explore, much less resolve these matters. Instead, it focuses on where the locus of the right to self-defence rests. An attack against a merchant ship could trigger the right to self-defence, but in defence of whom? While it may be too premature to derive answers on this question from the still unfolding set of events involving Iran’s seizure of the MSC Aries, the same cannot be said about the Anglo-American hostilities against the Yemen based Houthis.

This April marks the fourth running month of Anglo-American naval forces’ engagement in combat off Yemen. These forces have endured a frequency of attacks last experienced over 80 years ago during the Second World War. The exchanges began on January 11, 2024, when the U.S. and UK armed forces conducted a joint strike in Yemen with non-operational support from Australia, Canada, the Netherlands, and Bahrain. The trigger for this Anglo-American use of force stemmed from two incidents. The first was the Houthis’ targeting of military and commercial vessels on January 9, 2024. The second was the Houthis’ targeting of numerous merchant vessels between November 19, 2023 and January 09, 2024.

It is relatively uncontroversial that the facts of the first incident were sufficient to trigger the Anglo-American right of self-defence (Kraska). This post addresses an aspect of the second set of events regarding the right to self-defence in the case of attacks on merchant shipping. In particular, which State can exercise the right to self-defence in response to attacks on merchant vessels?

Bases for the Use of Force

Since November 19, 2023, the Houthis have been targeting merchant vessels transiting the Red Sea and beyond, purportedly in support of Gaza’s Palestinians. Houthi actions triggered the creation of a U.S.-led defensive multinational coalition in December, which launched Operation Prosperity Guardian to help safeguard commercial traffic. January 9, 2024, marked a significant escalation, with Houthi forces launching a large-scale attack on military and commercial vessels which resulted in U.S. and UK naval forces shooting down eighteen unmanned aerial vehicles, two anti-ship cruise missiles, and one anti-ship ballistic missile.

Following the passage of UN Security Council (UNSC) Resolution 2722 on January 10, 2024, and independent of Operation Prosperity Guardian, the U.S. and UK armed forces conducted a joint strike in Yemen, with non-operational support from Australia, Canada, the Netherlands, and Bahrain. The United States and United Kingdom reported both strikes to the UNSC, where both justified their use of force on their inherent right to exercise self-defence, as reflected in Article 51 of the UN Charter.

In its letter to the UNSC reporting its actions, the United States clearly stated that its attack was “in response to a series of armed attacks by Houthi militants over the last few months, including several attacks against United States Navy ships in the Red Sea.” The United Kingdom’s letter stated that its attack was in response to “the armed attack against HMS Diamond and the ongoing risk to British ships.” Both letters also referenced the passage of UNSC Resolution 2722, which affirmed the navigational rights and freedoms of “merchant and commercial vessels” and took note of the right of States to “defend their vessels from attacks.” The joint statement of January 12, 2024, by the States which participated in the Anglo-American strikes also acknowledged that these strikes were conducted in response to the “Houthi attacks against vessels, including commercial shipping, transiting the Red Sea.”

Recourse to the use of force under Article 51 of the UN Charter is conditional on a State having been the victim of an armed attack. A perusal of these documents makes it evident that the “armed attack,” which triggered the Anglo-American recourse to the use of force, is comprised of two sets of independent, but possibly overlapping, events. The first set of events concerns the attacks on January 9, 2024, which targeted military vessels as well as merchant vessels. In the Oil Platforms case (para. 72), the International Court of Justice (ICJ) acknowledged that an attack on a single military vessel may be sufficient to allow an invocation of the right of self-defence. Indeed, there is a fairly strong consensus that the events of January 9, 2024, were sufficient to constitute an armed attack by themselves (see e.g., here, here, and here). Relatedly, the question of whether the Anglo-American actions satisfied the tests of necessity and proportionality is an entirely different matter that has already been tackled by Stefan Talmon and Christian Henderson.

However, the truly interesting part of the Anglo-American submissions concerns the second set of events and the question whether attacks on merchant vessels give rise to the right of self defence. It is unclear from the letters what weight the United States and the United Kingdom intended to give to the January 9 attack on the one hand and the months-long Houthi targeting of merchant vessels on the other. While it is clear that the former constitutes an armed attack by itself, the language of the Anglo-American submissions indicates that the latter also had a role to play.

Merchant Ships and the Right to Self-Defence

UNGA Resolution 3314 (XXIX), which provides a definition of aggression, indicates in Article 3, a list of actions that qualify as acts of aggression. Though the concepts of aggression and armed attack do not necessarily coincide fully (Nolte and Randelzhofer, paras. 17-18), the ICJ has in numerous instances implicitly linked the two concepts (Trapp, p. 683). Also, in its work, the International Law Commission has employed the two terms rather interchangeably (Tladi, para. 62). Article 3(d) of this resolution envisages that an attack on the “marine fleets of another state” can qualify as an act of aggression. However, as Martin Fink observes, this sentence employs the phrase fleet and not ship. While it is possible to have a legitimate difference of views on exactly what the term “fleet” denotes, one ship alone cannot constitute a fleet. Similarly, there exists a flourishing debate on whether an attack on a merchant vessel, when repeated or combined with other attacks, could justify a resort to the use of force extending beyond an on-the-spot reaction.

The Houthis have been targeting merchant vessels transiting the Red Sea and beyond since November 19, 2023. Between that date and January 9, 2024, at least seventeen distinct attacks on merchant vessels occurred. These include attacks on four Liberian flagged vessels (MV Central Park, Al Jasrah, MSC Palatium III, MSC United VIII), three Panamian flagged vessels (M/V Number 9, MSC Clara), two Bahaman flagged vessels (MV Galaxy Leader, M/V Unity Explorer), two Norwegian flagged vessels (MV Strinda, M/V Blaamanen) and one flagged vessel each of the Marshall Islands (MV Ardamore Tanker), Hong Kong (MV Maersk Gibraltar), India (M/V Saibaba), Singapore (Maersk Hanghzhou) and the Cayman Islands (Swan Atlantic). The joint strike of January 11, 2024, involved Anglo-American forces assisted by Australia, Canada, the Netherlands, and Bahrain, yet not a single one of the attacked vessels flew the flag of any of these States. The Swan Atlantic, flagged in the Cayman Islands represents the only exception. As a British Overseas Territory, the UK bears responsibility for the defence of the Cayman Islands. Given this link, there is room for the United Kingdom to consider the attack on the Swan Atlantic as an action that could implicate its recourse to the right to self-defence.

In the Oil Platforms case, the ICJ failed to make its views known on whether an attack on a merchant vessel could trigger the right to self-defence. However, given the clear language of Article 3(d) of UN General Assembly Resolution 3314, which uses the term “fleet” rather than “ship” or “vessel,” the United Kingdom is precluded from claiming that this attack alone could have triggered the legal threshold of an armed attack. Consequently, insofar as a right to exercise self-defence from an attack on merchant shipping does arise, the holder of that right would be a State other than those that conducted the January 11, 2024, strikes in Yemen (Oil Platforms, para. 64).

The right of third States to exercise self-defence on behalf of or with injured States in this instance seems similarly unavailable. The ICJ has made clear that an attack by State A against B does not allow State C to attack A, unless State B first declares that it has been subjected to an armed attack and then explicitly requests State C to use force in collective self-defence (Nicaragua, paras. 195 and 199). However, in the case of the Houthis, none of the concerned flag States issued a request for collective self-defence to the perpetrators of the January 11, 2024, strikes into Yemen. And as ably addressed elsewhere, there exists no authority to use force independent of Article 51 within UNSC Resolution 2722.

Indeed, in UNSC discussions, only Japan expressed unqualified support for the Anglo-American actions. Instead, the view was expressed that the Anglo-American strikes were rooted in a misinterpretation of Resolution 2722 and that they introduced an unnecessary and escalatory dynamic to the situation. Russia, China, and Switzerland all united in calling out either the improper legal foundations or the extent of the Anglo-American strikes.

Flags of Convenience and the Genuine Link

Except in one instance, the Houthi strikes did not target any ships flying the flag of the States which launched the January 11, 2024, attack. And yet, in their UNSC submissions, both the United States and the United Kingdom referred to the months-long attacks against over a dozen ships as part of the events that constitute “armed attacks,” in response to which they exercised their right to self-defence. While these facts may seem contradictory, it would be a grave error to conclude that these ships were not in any way linked to the States involved in the January 11 attacks. A glance behind the flags flown, reveals that over two-thirds of the targeted ships have ownership and/or management structures based out of Europe, with over half of them being located in just two countries: the United Kingdom and Switzerland.

The manner of nationality allocation to ships has long been a thinly-veiled secret of the shipping industry. Since at least the mid-twentieth century, the shipping industry has used open registries also called flags of convenience to affiliate with States with which it may share no genuine link at all. Under this system, a ship can acquire a State’s nationality merely because a State official declares that it is so. Consequently, a ship can obtain a State’s nationality irrespective of whether nationals of that State are involved in the ownership or manning of the ship, or whether the company that owns the ship has its principal place of business within that State. In a largely peaceful world, which has now experienced a multi-generational period without any general naval war (p. 426-29), this system has come to represent the normal state of affairs.

The International Tribunal for the Law of the Sea (ITLOS) has also sanctified this practice over the course of multiple (paras. 82-83) judgments (para. 110). The ITLOS has ruled that the requirement of a “genuine link is concerned merely with a flag State’s duty to effectively exercise jurisdiction and control in administrative, technical, and social matters,” as opposed to representing a condition sine qua non for there to be a grant of nationality. These findings were not without dissent (para. 47), with some ITLOS judges noting the impossibility of exercising jurisdiction and control over a ship absent the ability to exercise a similar authority over the owners or the charterer/operator (p. 254-55).

Furthermore, as noted by prominent legal scholars (p. 69-70), the ITLOS arrived at this conclusion on the basis of a dubious legal interpretation. In addition to engaging in a selective reading of the travaux préparatoires, the ITLOS interpreted the relevant primary law in a manner which was inconsistent with the Vienna Convention on the Law of Treaties. The ITLOS justified its conclusion based on a combined reading of Articles 91 (ship nationality) and 94 (flag State duties) of the United Nations Convention on the Law of the Sea. The ITLOS’s reading elevated Article 94 to the general rule, thus making Article 91 ancillary to Article 94. Consequently, the ITLOS rendered Article 91 meaningless in direct contravention of the principle of effet utile(effectiveness), which requires that a treaty be interpreted in a manner which gives effect to every term of a treaty, as opposed to rendering parts of it useless or redundant (See e.g. Churchill, et al.).

The consequence of these developments, as noted by the United Nations Conference on Trade and Development (p. 32), is that we now live in a paradoxical world where the “country of the flag is not necessarily connected to the nationality of the vessel’s owner.” This has led to the concentration of vessel registration services in small island, developing States and the least developed countries due to the availability of beneficial tax regimes and cheap labour.

Nationality and Self-Defence in Peace and War

The conferral of nationality and registration has always served both a private and a public function. Among the primary public law functions discharged by nationality and registration is the determination of rights relating to naval and political protection and the use of ships during war. As is evident in the Houthi case, an examination of nationality becomes a necessary aspect of any self-defence analysis, because this is the juridical link which produces the network of mutual rights and obligations between the State and a ship.

Affording greater importance to the existence of a genuine link, as opposed to the mere existence of a registration, is admittedly at odds with the currently entrenched understanding of ship nationality. However, recognizing an understanding of nationality based on a genuine link provides the best explanation for reconciling the otherwise contradictory set of facts highlighted in the preceding sub-section. Of the ships targeted between November 19, 2023, and January 09, 2024, almost a third of all the ships have British ownership or management. Operating with this alternative understanding of ship nationality allows the possibility of including these attacks within the assessment of whether the threshold of an armed attack was breached. Given the explicit British declaration that it was subject to an armed attack, this understanding satisfies the requirements of the law of collective self-defence, providing an additional basis of support for the legality of the American actions as well.

In relation to the ongoing Russian war of aggression in Ukraine, numerous States, including the United States and the United Kingdom, have already embraced this understanding of ship nationality. In sanctioning Russia, both the United Kingdom and the United States have gone well beyond focusing on only those ships that fly the Russian flag. The United Kingdom, for example, has imposed prohibitions on ships “owned, controlled, chartered or operated by persons connected with Russia” while the United States has also imposed prohibitions on both Russian-owned and Russian-operated vessels.

In early January 2024, Professor James Kraska expressed the opinion that the law of armed conflict (LOAC) represented the correct paradigm to guide the conduct of the Anglo-American forces. Since that date, the Royal Navy experienced its biggest attack in decades and the U.S. Navy’s deployed assets have been operating while enduring hostile attacks at a rate unmatched since the 1940s. Given these developments, Professor Kraska’s views about the applicability of the LOAC have undoubtedly gained strength.

The Law of Naval Warfare (LNW) has always recognized—consistently and unambiguously—that the veil of a ship’s registration can be pierced to determine a ship’s nationality and possible enemy character. The method for determining enemy character is not just a ship’s registration, but also the ownership or charter of the vessel. Indeed, in the months following the January confrontations, the Houthis themselves sought to “ban” all vessels linked to Israel, the United States, and the United Kingdom from sailing in its surrounding waters. Notably, in implementing this ban, the Houthis clearly stated that it is not just ships sailing under Israeli, U.S. and UK flags that are banned, but also any ships owned by Israeli, U.S. or UK individuals or entities.

However, relying on these provisions of the LNW in relation to the current situation runs up against a further difficulty related to the characterization of the conflict. The application of the LNW in a non-international armed conflict (NIAC) gives rise to many challenges. For instance, the Newport Manual recognizes (§ 2.2.4) that the rules and principles of the LNW governing the relations between the parties to the conflict can apply in a NIAC. However, the Manual notes that this is not normally the case in relation to prize law or the law of maritime neutrality. This is important to note because these are precisely the branches of the law in relation to which the determination of enemy character assumes centerstage. However, the Newport Manual also observes that prize and neutrality law can become applicable in cases where there has been a recognition of belligerency or if the conflict possesses the trappings of an international armed conflict. The correct resolution of these interconnected issues has immense bearing on whether the LNW framework for determining nationality and enemy character should apply.

Concluding Thoughts

Commercial expediency, in a multi-generational period characterized by the absence of general naval war, has given rise to a historically anomalous state of affairs. The private functions of the conferral of nationality and registration have taken priority over the concurrent public functions. However, recent State practice, particularly during the Russo-Ukrainian war, has marked a turning point. The end of the Cold War marked the victory of the Washington Consensus, with its clear tilt in favour of the markets as opposed to governments. The decades following the end of the Cold-War witnessed an all-out push for hyper-globalization. The attempt to remove all the barriers that hindered the flow of trade and capital resulted in the creation of truly global supply chains.

This was a world order that was well suited to privileging the private functions of ship nationality at the cost of its public functions. However, that world does not exist any longer. In an international order that is now characterized chiefly by the death of the Washington Consensus and a partial retreat from globalization, the ongoing conflict with the Houthis presents but another example of the long overdue need to recalibrate the balance between the private and public functions of nationality. This is an issue whose ramifications go far beyond the current conflict. Over 80% of the global merchandise trade by volume and 70% by value is transported by sea. This is why in an international order characterized not just by interdependent economies but also by interdependent production processes, the consequences of the interdiction of these flows would have catastrophic consequences not just for the involved belligerents but rather for the entire international society. Consequently, there exists a prior question, the resolution of which is even more important than the question whether attacks on merchant shipping trigger the right of self-defence. In a world where a country’s flag is no longer a reliable indicator of the vessel owner’s nationality or manning, which State is entitled to exercise the right to self-defence for an attack on merchant shipping?

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Himanil Raina is a PhD candidate and a Teaching Assistant at the Department of International Law at the Geneva Graduate Institute.

Photo credit: Antony Mustow