The United Nations Convention on the Law of the Sea (UNCLOS) establishes different regimes for navigation through straits important for global trade. Articles 37–44 regulate transit routes in straits connecting the high seas or exclusive economic zones, giving ships and aircraft the right of uninterrupted and expeditious passage without hindrance from coastal States. This non-suspension regime applies to critical chokepoints such as the Strait of Hormuz and Bab el-Mandeb, where territorial seas overlap.
In contrast, Articles 19–22 define innocent passage through the territorial sea, permitting navigation that is not harmful to the peace, good order or security of the coastal State. The route must be continuous and expeditious, except for activities such as weapons practice or intelligence gathering. For straits that do not qualify for transit passage, Article 45 ensures non-suspended innocent passage.
There exists a significant technical difference between the two regimes which has major implications for naval operations: under transit passage, submarines can remain submerged as this is a ‘normal mode’ of operation for such ships. However, under innocent passage, submarines must surface and show their flag. This difference is a constant source of tension between naval powers, who support submerged transit as a customary right, and coastal states, who want greater visibility over military movements through their territorial waters. The table below summarizes the key differences between these two regimes.
Coastal states retain significant regulatory powers under UNCLOS, thereby balancing freedom of navigation with sovereignty. Article 42 allows laws on safety of navigation, maritime traffic regulation, pollution prevention and customs. Maritime traffic services, such as those in the Strait of Malacca, exemplify the provisions of Article 41 for mandatory routing systems without hindering transit.
For archipelagic sea routes, such as near Malacca, Indonesia, the route mirrors transit rights but requires designation by archipelagic states. Pollution control conforms to international standards, yet states should avoid undue interference. These rights extend to the protection of the marine environment, although enforcement remains state-driven.
In particular, there is a growing trend towards what might be called ‘environmental law’, whereby coastal states invoke Article 21, which allows regulations on pollution and navigation safety, as a pretext to detain or inspect ships for political purposes. Both Iran and Malaysia have adopted environmental and security pretexts to claim regulatory advantages over commercial and naval shipping. While UNCLOS allows such rules in principle, their selective application as a means of geopolitical pressure is in an uncomfortable gray zone.
The Strait of Hormuz, located on the border of Iran and Oman, is a transit route despite being within the territorial sea, ensuring uninterrupted flow of about 20% of global oil. The Bab el-Mandeb, linking the Red Sea to the Gulf of Aden, similarly benefits from Article 37, handling about 12% of world trade.
The Straits of Malacca and Singapore comprise the transit route with archipelagic provisions for Indonesia and Malaysia. Coastal states such as Iran cannot suspend passage even amid rising tensions, because transit passage operates as a lex specialis, a special legal rule that overrides the common law (lex generalis) of innocent passage in these specific straits. Article 38 prohibits obstructions, although ambiguities in the ‘normal methods’ of navigation, particularly in relation to submarines and unmanned vessels, continue to generate interpretative disputes.
UNCLOS prohibits the suspension of transit routes even in the event of conflict, and gives priority to freedom of navigation over countermeasures. Self-defense may justify temporary measures in extremism under Article 51 of the UN Charter, but interruptions in naval warfare require prior notification and proportionality in accordance with the San Remo Manual on International Law Applicable to Armed Conflicts at Sea. It is emphasized that the San Remo Manual is not a treaty; It is a scholarly codification of customary law and best practice. Thus, it has persuasive force rather than binding force, which is an important way to explain why belligerents often ignore its provisions in practice.
Belligerents can interdict enemy ships or mine routes, yet neutral shipping has protection from imminent danger. Iran’s periodic threats to close the Strait of Hormuz give rise to claims of aggression, but UNCLOS prevails over unilateral countermeasures. However, coastal States may take action under Article 19 against non-innocent routes, for example, those that pose a credible security threat, provided they do not completely suspend the transit route arrangement.
Another complication arises from America’s situation. As a non-signatory to UNCLOS, the US nevertheless treats transit route provisions as customary international law, arguing that these norms are subsumed into a common corpus of binding rules applicable to all states regardless of treaty ratification. This allows the US to assert and enforce transit rights, including freedom of navigation operations, without formally accepting UNCLOS jurisdiction, a stance that is disputed both practically and legally.
Houthi attacks in the Red Sea from November 2023 exemplify chokepoint vulnerabilities, with more than 130 attacks on commercial vessels transiting through the Bab el-Mandeb, halving Suez Canal traffic and a sharp increase in global freight costs. Renewed threats amid rising Iran-related tensions threaten to lead to a full blockade in 2026, which would result in a material impact on grain and oil imports into dependent economies.
The Strait of Hormuz has seen a series of Iranian occupation and apparent closure threats following US military and sanctions actions, testing the limits of transit passage rights without formally triggering their suspension. Incidents in the Strait of Malacca remain comparatively low-level, focusing on piracy rather than state action. Collectively, these events have forced considerable shipping traffic to be re-routed around the Cape of Good Hope, adding ten to 14 days to travel times and exposing the vulnerabilities of global supply chains at times of need.
A particularly significant development is the emergence of anti-access/area denial (A2/AD) capabilities, precision drones, ballistic missiles, and maritime mines deployed by both state and non-state actors. These technologies allow hostile parties to create de facto blockades without legal formality, rendering the international legal framework effectively unable to classify or respond to the threat in real time. The Houthi campaign in the Red Sea is the most prominent contemporary example of this phenomenon, and its implications for maritime law are deep and as yet unresolved.
The International Tribunal for the Law of the Sea (ITLOS) affirms coastal duties: ‘Coastal States must allow innocent passage of foreign ships, but may take action against passages that are not innocent,’ exercising jurisdiction under UNCLOS. However, it is important to note that ITLOS has jurisdiction only where both parties to the dispute have agreed to, either directly or through the ratification of UNCLOS. This limitation makes the tribunal largely irrelevant in disputes involving the US, which has not ratified the convention, or non-state actors such as the Houthi movement, which are completely outside the treaty framework.
IMO Secretary-General Arsenio Dominguez highlighted the broader geopolitical dimension, warning that ships and seafarers have increasingly become leverage in geopolitical disputes, a phenomenon clearly visible in the Hormuz crisis. UNCTAD’s Rebecca Grinspan has similarly cautioned that maritime chokepoints are particularly vulnerable to disruptions, be they climate-related, economic, geopolitical or operational, a warning that the events of 2025 and 2026 have done nothing to assuage.
UNCLOS lacks real-time enforcement capacity, relying on slow-moving tribunals such as ITLOS, which enables legal ambiguity to be exploited during active crises. The ambiguities surrounding what constitutes ‘prejudicial’ activities under Article 19, combined with the contested interplay between UNCLOS and UN Charter self-defense provisions, create significant interpretive leeway for states such as Iran, Russia and China to act in ways that are technically contested but practically unchallenged.
No rapid-response protocol exists for chokepoint breaches. The IMO lacks enforcement powers, and the UN Security Council is routinely paralyzed by regional and geopolitical divisions. Non-signatories such as the US customarily adhere but selectively, while hybrid threats involving drones, sub-sea cables and precision missiles have widely superseded the intentions of the drafters. The actual blockade problem posed by A2/AD systems is particularly acute: UNCLOS was written for a world of surface ships and conventional naval operations, not for a world in which a non-state actor with access to Iranian-supplied drones could effectively close an international strait to commercial traffic.
Regional forums, such as the proposed Gulf Maritime Security Forum, can begin to bridge these institutional gaps by promoting cooperation between coastal and user states. More ambitiously, the IMO-led Blue Corridor Protocol, establishing protected lanes with internationally monitored safe passage guarantees for merchant vessels in active conflict areas, would represent a meaningful structural reform. Yet, enforcement ultimately depends on power dynamics and political will, underscoring the inherent resilience of UNCLOS as a framework, even as the 2026 dual chokepoint tensions test its limits.
(Views expressed are personal)
This article is written by Ananya Raj Kakoti, Scholar, International Relations, Jawaharlal Nehru University, New Delhi.
