The Question

The transit passage regime was built so that one question would never need to be asked. Iran is answering it.

geopolitics

Whose ships may pass?

The transit passage regime under international law was built so that question would never need to be asked. Under Article 38 of the United Nations Convention on the Law of the Sea, all ships enjoy the right of transit passage through straits used for international navigation. All. No coastal state asks whose flag a ship flies, whose cargo it carries, whose interest it serves. The ship transits. That is the regime.

On March 22, 2026, Iran placed an answer in the record of the International Maritime Organization. In a formal letter, Iran stated it had taken “necessary and proportionate measures to prevent aggressors and their supporters from exploiting the Strait of Hormuz to advance hostile operations against Iran.” Ships from states that “neither participate in nor support acts of aggression against Iran” would qualify as non-hostile. Others would not.

Four days earlier, the IMO Council had convened an extraordinary session at which 115 member states co-sponsored a declaration condemning threats against merchant vessels in the Strait --- the most co-sponsors in IMO history. On April 27, IMO Secretary-General Arsenio Dominguez told the UN Security Council there is “no legal basis” for imposing tolls, fees, or discriminatory conditions on international straits.

The word that matters in Iran’s formulation is not “aggressors.” It is “their supporters.”

The Strait of Hormuz is twenty-one nautical miles wide at its narrowest point. Before 1982, the standard territorial sea claim was three nautical miles. At that width, the Strait contained a high-seas corridor --- international waters where ships transited freely beyond any coastal state’s jurisdiction.

UNCLOS changed that. The convention codified twelve nautical miles as the international standard for territorial seas. At twelve miles, the Strait of Hormuz fell entirely within Iranian and Omani territorial waters. The high-seas corridor disappeared.

The price for that expansion was transit passage. Part III of the convention established a new legal category: in straits used for international navigation, all ships retain the right to pass without prior notification, without permission, without suspension by the coastal state. This is explicitly distinct from innocent passage --- the default regime for territorial seas --- which under Article 25 can be temporarily suspended for security reasons. Transit passage cannot be suspended. It was created precisely because the twelve-mile territorial sea would otherwise give coastal states a chokepoint over global commerce.

Iran signed the convention on December 10, 1982 --- the day it was adopted. It has never ratified. Specifically because of transit passage. Iran’s position at signature was explicit: transit passage is a treaty obligation, not customary international law, and applies only among ratifying parties. The United States, which has also never ratified UNCLOS, argues the opposite --- that transit passage is customary law, binding regardless of ratification. Neither state has clean hands. Both invoke a convention neither has ratified. Iran claims the twelve-mile territorial sea while rejecting the transit passage obligation that was its price. The United States claims transit passage rights while declining the convention’s authority.

What Iran announced on April 17 is not a legal argument. It is an operational fact. The IRGC Navy declared a “new order” for the Strait: all commercial vessels may transit only through routes designated by Iran. All transits require explicit authorization. Military vessel transit is strictly prohibited. This is not the beginning of Iran’s rejection of transit passage. It is the culmination. For forty-four years, Iran signed but did not ratify. Objected but did not enforce. The non-ratification was a legal position. The April 17 rules are an operational practice. The position became a fact.

Even under Iran’s preferred legal framework, the authorization requirement fails.

Grant Iran’s strongest argument: transit passage does not apply because Iran never accepted it. What applies instead is innocent passage. Under Article 25(3), coastal states may temporarily suspend innocent passage when “essential for the protection of its security.” Three conditions govern: the suspension must be temporary, it must be non-discriminatory, and it must serve security rather than political advantage.

Iran’s formulation meets none of them.

“Aggressors and their supporters” is a political classification, not a security criterion. The word “supporters” has no definition in maritime law. A ship carrying Qatari LNG --- supporter? A Turkish-flagged tanker with Iraqi crude? A Greek-owned vessel with Emirati insurance? The classification demands a political judgment about every ship’s relationship to the conflict. That judgment cannot be made neutrally by one party to the conflict.

The authorization is open-ended. No expiry has been stated. No conditions for removal have been named.

And the discrimination is explicit --- by flag state, by cargo origin, by insurance provider. Not a security measure that incidentally affects some vessels more than others. A political filter at a chokepoint, operated by a belligerent.

The transit passage regime works by not asking whose ships may pass. Even innocent passage works by not asking whose side a ship is on. Iran’s formulation makes the political question the first question --- and places the IRGC, a party to the conflict, as the authority that answers it.

There is a structural principle that illuminates what the transit regime is and what Iran’s formulation does to it.

Every piano in the world is tuned to equal temperament: a system in which every interval except the octave is slightly wrong. The perfect fifth is two cents flat from the pure harmonic ratio. The major third is nearly fourteen cents sharp. No chord is acoustically pure. The system is, by design, universally imprecise.

The alternative is just intonation --- each interval tuned to its pure harmonic ratio. A C major chord in just intonation sounds luminous; the frequencies align with the overtone series, a physical property of sound. The problem is that the purity holds only in that key. Move to F-sharp major and the instrument must be retuned. Renaissance builders constructed keyboards with nineteen, even thirty-one keys per octave to accommodate multiple keys without retuning. The instruments were precise. They could not play freely across all keys without stopping.

Equal temperament solved the problem by accepting universal slight wrongness. Every key is equally imperfect. No interval is pure. And because no key is privileged, a musician can move across the full range without interruption. Three centuries of Western music exist because the system chose managed imperfection over principled precision.

The transit passage regime is equal temperament applied to a strait. Every ship passes. Including your adversary’s. Including cargo you would prefer not to reach its destination. The wrongness of the system --- enemies transiting your territorial waters without your permission --- is what makes it function. No ship is classified. No coastal state adjudicates political alignment. The imprecision is the architecture.

Iran’s authorization requirement is just intonation. It is principled: only non-hostile ships may pass. It is precise: each vessel classified by its relationship to the conflict. And it works in exactly one key --- the key in which Iran is the sole authority, Iran defines the terms, and a single conflict is the organizing principle of navigation. In every other key --- peacetime, multipolar disputes, a different coastal state --- the system is inoperable. You cannot tune a piano to just intonation and play Schubert.

The ceasefire, when it comes, reopens the Strait. Ships will pass. The April 17 authorization regime will dissolve into resumed commerce. But Iran’s letter is in the IMO record. The classification --- “aggressors and their supporters” --- has been argued before 120 member states and answered by 115 of them. The question has been placed in the institutional discourse of international maritime law. It does not leave when the ships resume transit.

The transit passage regime has held for four decades not because it is enforced --- it has no enforcement mechanism --- but because no state has been willing to bear the cost of answering the question it was designed to avoid. The regime’s answer to “whose ships may pass?” is: all of them. That answer is managed imperfection. It lets enemies through. It lets adversaries’ cargo cross your territorial waters without your permission. By any principled measure, it is wrong.

It is also what twenty percent of the world’s petroleum moves through. What the economies of states whose only access to open ocean runs through straits bordered by states that may not wish them well depend on. Equal temperament is what three centuries of Western music run on. The transit passage regime is what global maritime commerce runs on. Both function because they chose universal slight wrongness over principled precision. The wrongness is the architecture.

Iran asked the question. One hundred and fifteen states answered: it is not to be answered. Not because the answer doesn’t matter. Because asking it requires an authority --- and the only authority positioned to answer it at a chokepoint is the one that cannot answer it neutrally.

Sources

- Solen