Did Operation Prosperity Guardian adhere to the principles of international law, or did it transgress legal boundaries in pursuit of strategic objectives?
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On 19 June 2024, a Greek coal carrier sank to the bottom of the Red Sea a few days after it was abandoned due to the damage sustained during an attack by Yemen’s Houthi militants.
This attack on the commercial ship was just one of the numerous attacks that the militant group has conducted, targeting military and civilian ships in the Red Sea. These attacks are a show of solidarity with the Palestinians over Israel’s war on Gaza.
In response to these attacks in the Red Sea, on 10 January 2024, the United Nations Security Council (UNSC) adopted Resolution 2722 (2024), condemning and demanding an immediate halt on attacks by Houthis on merchant and commercial vessels, underscoring the navigational rights and freedoms and most importantly, affirming the rights of the member states to defend their vessels against attacks as per international law.
In response to these attacks in the Red Sea, on 10 January 2024, the United Nations Security Council (UNSC) adopted Resolution 2722 (2024), condemning and demanding an immediate halt on attacks by Houthis on merchant and commercial vessels.
The very next day, on 11 January 2024, an air campaign spearheaded by the United States (US) and United Kingdom (UK) and supported by Australia, Bahrain, Canada, and the Netherlands called Operation Prosperity Guardian (OPG), targeted Houthi facilities in Yemen to ‘degrade the Houthi’s operation capacity’ and ‘ensuring freedom of navigation for all countries’.
OPG, while achieving partial success in its objectives, has not fully deterred the Houthi aggression against maritime vessels in the Red Sea. This limited efficacy, coupled with vocal condemnation from nations such as Russia, Iran, and China on grounds of alleged breaches of international law, has ignited a fiery debate within the global community. At the heart of this controversy lies a fundamental question that challenges the very foundation of international legal norms and the use of force in the modern era: Did OPG adhere to the principles of international law, or did it transgress established legal boundaries in pursuit of strategic objectives?
Immediately after conducting the strikes, both the US and UK in separate letters to the UNSC, expressly mentioned that the strikes against the Houthis were conducted as per their inherent right to self-defence laid out in Article 51 of the UN Charter.
Article 51 of the UN Charter states that “Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations until the Security Council has taken measures necessary to maintain international peace and security. Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such action as it deems necessary in order to maintain or restore international peace and security.”
Some experts have rightly questioned whether the inherent right of self-defence for states arises in case their merchant ships are attacked. Although this question is of immense importance and largely remains unsettled, it does not truly arise in the present case. Both the letters of the US and the UK addressed to the UNSC have justified military action based on attacks on merchant as well as naval ships by Houthis as grounds for self-defence. Since it is established under international law that an attack against the armed forces of a state, which may or may not be within the territory of that state can trigger the right to self-defence, this condition stands fulfilled.
Some experts have rightly questioned whether the inherent right of self-defence for states arises in case their merchant ships are attacked.
Secondly, it needs to be established that an armed attack against a member state took place for the inherent right to self-defence to come into place. Under the current international law regime, armed attack has been defined as a ‘grave use of force’ that has sufficient ‘scale and effect’. From ICJ’s judgement in the Oil Platforms case, it has become evident that the test for an armed attack is highly contextual, varying from case to case. In the current context, the UK’s warships and United States’ military aircraft were attacked with sophisticated weapons such as unmanned aerial vehicles, anti-ship missiles, and even combat aircraft. The British Prime Minister even states that this was the ‘biggest attack on the Royal Navy for decades’. Arguably, this should fall under the definition of an ‘armed attack’.
Another important question which arises is if both countries were within their rights when they attacked the facilities of a non-state actor situated within the jurisdiction of a UN member state. The International Court of Justice (ICJ) advocates that they are not, as reflected in its Advisory Opinion, 2004. However, others think that ICJ’s stand is incorrect since the language of Article 51 does not indicate that the perpetrator of an armed attack necessarily must be a state. Moreover, the UNSC has on more than one occasion mentioned the right to self-defence in case of attacks by a non-state actor, such as Al-Qaeda. Finally, the US has previously adopted the argument of self-defence when attacking a non-state actor in another state without obtaining its permission, such as in Afghanistan and Syria. So even though attacking Houthi facilities in Yemen in this context could be considered a legally grey area, the action could very well be considered part the customary international law.
While these arguments may be in favour of OPG, there are several which are not.
Both the UK and the US have relied heavily on UNSC Resolution 2722 (2024), however, it has in no way established a legal basis for the use of force against the Houthis since under Chapter VII of the UN Charter, it was not a ‘decision’ and hence did not grant authority to any state for the military action. The Resolution even went on to emphasise ‘respect for the sovereignty and territorial integrity of the coastal States of the Red Sea’. Even the Swiss representative to the UNSC went on to reiterate the difference between a State’s inherent right to self-defence and its right to defend its vessels from attack, stating that any military operation that goes beyond this immediate protection need would be disproportionate—and not covered by the Resolution.
Both the UK and the US have relied heavily on UNSC Resolution 2722 (2024), however, it has in no way established a legal basis for the use of force against the Houthis since under Chapter VII of the UN Charter, it was not a ‘decision’ and hence did not grant authority to any state for the military action.
In the Nicaragua Case, the ICJ emphasized the ‘criteria of necessity taken in self-defence’. The principle of necessity in international law dictates that force may only be employed to counter an ongoing armed attack. In the present case, the span of two days between the initial attack and the subsequent use of force raises questions about its legitimacy as an act of self-defence. The invocation of an “ongoing risk” or “continuing threat” by both nations falls short of the threshold required to justify anticipatory self-defence. Instead, their actions appear to be more aligned with deterrence or retaliation—objectives that, while strategically significant, do not fall within the legal framework of self-defence.
Situations such as these reflect the complex interplay between international law and geopolitical imperatives, challenging the traditional boundaries of justified military action in an increasingly volatile global landscape. Back in 1945, when the UN Charter came into effect, the idea that a non-state actor like the Houthis could spark such tensions was unimaginable.
The debate surrounding OPG's legality underscores international law's dynamic nature, evolving through varied interpretations. Experts may argue indefinitely without consensus, highlighting the malleability of legal frameworks in the face of emerging threats. This episode reveals the enduring influence of power dynamics in shaping the international order. It serves as a stark reminder that, despite established legal norms, powerful nations can assert their will, regardless of international law.
As we navigate these challenges, the global community must adapt legal frameworks to address new threats while preserving principles of sovereignty and collective security.
Udayvir Ahuja is a Programme Coordinator for the Strategic Studies Programme at the Observer Research Foundation.
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Udayvir Ahuja is a Programme Coordinator for the Strategic Studies Program, where, beyond operational aspects, he engages in writing and researching on contemporary subjects within ...
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