Legal and Operational Issues in the Strait of Hormuz: Transit Passage Under Fire

Iran’s attacks on neutral shipping and potential mining of the Strait of Hormuz violate both the law of the sea and the law of armed conflict—and reveal how difficult those rules are to enforce in practice.

The Strait of Hormuz — a narrow chokepoint through which roughly 20 percent of the world’s oil transits — is now an active conflict zone. Iranian forces have struck multiple neutral merchant vessels and may be laying naval mines in the Strait, threatening one of the most important shipping routes in the global economy.

Secretary of Defense Pete Hegseth has told the world that “we don’t need to worry about it.”  I disagree—the security situation in the Strait is a source of immense worry, is acutely dangerous, and there is no easy fix. What’s more, as I discuss below, the U.S. Navy’s very recent decommissioning of an entire class of minesweepers, without an effective ready replacement, makes an already precarious situation worse. 

The Strait’s unique geography also provides a textbook case of asymmetric warfare that favors Iran; a naval mine or drone costing thousands can cause billions of dollars in economic or physical damage.  And the mere perception of such a threat is enough to shut the Strait down indefinitely.  During my own transits through the Strait as a naval officer aboard the aircraft carrier USS Constellation, the narrow geography and proximity of Iranian territory were impossible to ignore. Even in peacetime, we took significant force protection measures with helicopters airborne and aircraft on alert as ships passed through.

And today we are in far more dangerous times.

What’s more, there are reports that Iran may already be mining the Strait, a significant escalation that could shut down one of the world’s most critical shipping lanes, depending on the extent of the mining.  Any attempts to demine the Strait and engage in defensive mine countermeasures will be difficult, if not near impossible, during a raging armed conflict.  In the interim, maritime insurance rates are skyrocketing, fuel prices are rising, and merchant vessels laden with oil, gas, and fertilizer are staying clear of the Strait of Hormuz until their physical security can be guaranteed. 

Below, I address the key legal and operational questions that will define how the conflict over the Strait unfolds — and how international law constrains (or fails to constrain) Iran’s actions.

What law governs maritime shipping through the Strait of Hormuz?

The Strait of Hormuz is an international strait within the meaning of Article 37 of the UN Convention on the Law of the Sea (UNCLOS), which applies to straits “used for international navigation between one part of the high seas or an exclusive economic zone and another part of the high seas or an exclusive economic zone.”  The outbreak of hostilities does not necessarily suspend UNCLOS.  While the Strait of Hormuz is bordered by Iran to the north and Oman to the south, it is legally an international strait.  Iran does not own the Strait of Hormuz, but it can effectively control maritime movement through the Strait based on its physical proximity.  The Strait of Hormuz is legally distinct from the Turkish Straits linking the Mediterranean Sea with the Black Sea—a key waterway in the Russia-Ukraine War.  The Turkish Straits are governed by the Montreux Convention, where Turkey has special legal authorities to regulate maritime traffic.  

In the Strait of Hormuz,  the right of transit passage is afforded to all ships and aircraft that transit the strait, a permissive legal right that “shall not be impeded”—even in times of war.  All vessels and aircraft—military and civilian—have the legal prerogative to exercise the right of transit passage through the Strait of Hormuz, provided that these ships and aircraft proceed without delay through the Strait of Hormuz, transit in their normal modes of operation, and refrain from using force against any nation bordering the Strait.  Although Israel, Iran, and the United States are not parties to UNCLOS, the transit-passage regime for international straits is widely regarded as customary international law and binding on all States. Iran’s actions to block the strait are contrary to both the letter and spirit of UNCLOS and applicable customary international law.

What are the challenges in transiting the Strait of Hormuz?

Practically, the Strait of Hormuz is the only way to get oil, natural gas, fertilizer, and other goods from the Persian Gulf to international markets. Geographically, the Strait of Hormuz is extraordinarily narrow in parts, with just 20 miles separating Iran from Oman at one point in the Strait.  Naval officers and civilian mariners are rightfully wary of running aground—a real concern for heavily-laden oil tankers and merchant vessels. And there are just two narrow corridors within the Strait itself for entering and exiting the Persian Gulf, thus making it exceedingly easy to identify, track, and target any vessel that transits the Strait.  

While there are reports of 2,500 U.S. Marines deploying to the region, a successful occupation of the southern tip of Iran bordering the Strait will not by itself immunize shipping from threats.  And such an amphibious landing would be incredibly dangerous.  Iran has already demonstrated the capacity to launch Shaheed drones — with a range of 1,000 miles — from virtually anywhere in Iran.  The drone threat makes it difficult — if not impossible — to guarantee safe passage through the Strait within the foreseeable future.  

Are Iranian actions violating international law? Where do things stand?

Yes.  Reports indicate that Iran has targeted civilian merchant vessels from Thailand, Japan, and the Marshall Islands; up to 16 civilian vessels have been struck in total. Crewmembers and the vessels themselves are neutral — not belligerents — to the armed conflict with Iran.  These Iranian strikes unlawfully target neutral, civilian objects and violate the fundamental principle of distinguishing between civilian and military objectives under international humanitarian law. To be sure, there are key questions about the legality of the underlying legal justification for the war with Iran, as Kate Brannen, Tess Bridgman, and Ryan Goodman at Just Security have posed, but the attacks on civilian merchant vessels are clearly unlawful.

Does Iran have the capacity to mine the Strait of Hormuz?

Yes, and Iran possesses numerous naval mine variants that could be used.  According to the U.S. Defense Intelligence Agency, Iran has 5,000 naval mines in its arsenal and has likely planned for such a scenario for decades.  In 1988, a U.S. Navy vessel, the USS Samuel B. Roberts, struck a mine in the Persian Gulf laid by Iran, snapping the warship’s keel and nearly sinking the vessel. Naval mining technology has gotten much more sophisticated since that tragic incident.  And the Strait of Hormuz is just 200 feet deep at its narrowest point, plenty shallow to lay a minefield to halt or throttle traffic. 

Is mining the Strait of Hormuz lawful?

No.  While naval mining is not unlawful per se, placing mines in an international strait in a manner that effectively denies transit passage to neutral shipping is widely understood to violate both the law of naval warfare and the law of the sea.

Indeed, one of the earliest international humanitarian law treaties, the 1907 Hague VIII Convention on the “Laying of Automatic Submarine Contact Mines,” was negotiated in response to the widespread and destructive naval mining that took place in the Russo-Japanese War, which killed hundreds of civilians well after the war’s hostilities.  Hague VIII specifically prohibits the “lay[ing] of contact mines off the coast and ports of the enemy with the sole object of intercepting commercial shipping.” And Hague VIII specifies that unanchored contact mines (which Iran possesses) must become harmless within one hour after loss of control over them.  Anchored mines must become harmless as soon as they are broken from their moorings.  

In theory, a belligerent power may lawfully employ naval mines in an armed conflict, but mine placement in the Strait of Hormuz is illegal because there is no alternative convenient or commercially acceptable route available to neutral merchant shipping.  The San Remo Manual on International Law Applicable to Armed Conflicts at Sea emphasizes that belligerents may not mine international straits in a manner that effectively blocks neutral transit.  Here is the influential Newport Manual on the Law of Naval Warfare’s discussion on mining  straits during an active armed conflict:

Mining of a belligerent’s own waters within a strait where the right of transit passage or non-suspendable innocent passage applies . . . is lawful provided that an alternative convenient or commercially acceptable route is available to neutral merchant shipping.

The U.S. Navy’s Handbook on the Law of Naval Operations reiterates this prohibition, stating that naval mines may not be placed in a manner to deny transit passage of international straits.  Furthermore, there is a general obligation for States to take feasible precautions under the law of war—this applies when using naval mines; every possible precaution must be taken for the security of peaceful shipping. 

What are the Operational Risks in “Demining” the Strait of Hormuz?

Many.   Once an area has been mined, it is often virtually impossible to guarantee that it has been fully demined.  An oil tanker explosion with a naval mine would be an environmental disaster that would further halt shipping.  Following the armed conflict, Iran would have an affirmative obligation under Hague VIII to remove its own mines. Still, commercial shippers would have to trust Iran that this has taken place.   And removing mines is notoriously difficult.  Since 1997, a multinational naval mine clearance and ordnance disposal operation has been conducted in the Baltic Sea to clear and destroy an estimated 160,000 mines from the First and Second World Wars, and just 20% have been removed or destroyed. 

Complicating matters, at this very moment, the U.S. Navy is retiring its four Avenger-class minesweepers previously homeported in the Middle East and moving toward a different strategy. The new strategy for mine countermeasures is untested and focuses on using the Littoral Combat Ship (LCS) in combination with helicopter support, drones, and Explosive Ordnance Disposal personnel.  In an apparently shortsighted move, just one month before the Iran conflict began, the four Avenger-class minesweeper vessels left their home port of Bahrain to be decommissioned and scrapped in the Philadelphia Naval Shipyard.    The U.S. Navy acknowledges that the LCS “will always struggle to achieve the same level of Mine Countermeasure proficiency” as dedicated minesweepers.  It remains to be seen whether the combination of LCS, helicopters, Explosive Ordnance Disposal, and Navy-trained dolphins (with natural sonar capability) can fill the gap left behind by these departed minesweepers.  Finding naval mines in an international strait is already notoriously difficult, particularly in an international strait that has so much existing debris that camouflages the existence of mines.

Can U.S. Navy vessels escort civilian vessels transiting the Strait?

Yes, but transiting remains highly hazardous, and the U.S. Navy lacks the capacity to conduct counter–mine operations quickly and expeditiously.  During the Tanker Wars in the late 1980s, U.S. Navy warships escorted civilian tankers through the Strait of Hormuz, with many Kuwaiti vessels reflagged as American vessels.  The U.S. Navy has warships and other assets in the region that could assist with this mission, but the Navy is far smaller than the 1980s Navy with the retirement of the Oliver Hazard Perry-class frigates.  Quantity has its own quality, and escorting civilian tankers would both expose the Navy warships to Iranian naval mines and projectiles while taking the warships away from other potentially critical missions.  Unilateral, U.S.-only escort is not a viable option at this time. The United States should lay the groundwork to bring in other nations for a broader multinational escort initiative, an effort that President Trump has started to undertake at least in the past 24 hours.  But this, too, will be challenging. Japan, a longstanding U.S. ally, relies on the Middle East for 95% of its oil. Japanese leaders  have urged caution following Trump’s request to help secure shipping through the Strait of Hormuz, stating that such a deployment faces an “extremely high hurdle.” 

What does naval doctrine say about mine countermeasures?

Mine warfare under Navy doctrine encompasses the countering of enemy-laid mines to permit friendly maneuver.  Doctrine makes clear that the most effective means for countering a mine threat is to prevent the laying of mines in the first place—this is known as “offensive mine countermeasures.” Defensive countermeasures are designed to counter mines once they have been laid.   While it is hard to know with certainty whether Iran has mined the Strait of Hormuz, we may already be in the far, far more challenging defensive mine countermeasure phase. 

Navy doctrine requires ships and aircraft engaging in mine countermeasures to have adequate force protection if conducted in a hostile environment—a virtual impossibility at this time in light of the Shaheed drone threat. 

Where do we go from here?

Iran’s attacks on civilian merchant vessels are clear violations of the law of armed conflict — the principle of distinction between civilian and military objects is among the most foundational rules of IHL, and there is no plausible military justification for striking Thai, Japanese, or Marshallese-flagged commercial ships. If reports of mining are confirmed, that escalation compounds the violation: Hague VIII explicitly prohibits the use of mines to deny transit passage of international straits, and the obligation to protect neutral shipping from indiscriminate hazards is not suspended by armed conflict.

In any armed conflict, the enemy has a vote, and Iran has apparently voted to close, or sharply suppress transit through, the Strait of Hormuz.  Iran has correctly identified economic disruption as the pressure point most likely to advantage it in the ongoing war.  The Strait of Hormuz has long been recognized as one of the world’s most strategically vital and legally complex maritime passages. The current conflict has made concrete what legal scholars and naval strategists have long warned: international law provides robust protections for transit passage rights, but it provides no reliable mechanism for enforcing them when a State actor is willing to violate them at scale.

Secretary Hegseth’s dismissal of the Strait crisis limits the kind of active diplomatic and multilateral response that international law and operational realities demand.   The United States faces a shrunken surface fleet and an untested and transitional mine countermeasures capability.  The Strait’s geography inherently favors the defender. The Tanker War playbook of 1987-88 — convoy escort, reflagging, a large frigate fleet — is not readily available in 2026.  If mining occurs, restoring safe transit will likely require a multinational naval effort and weeks of painstaking mine-countermeasure operations. 

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The crisis in the Strait of Hormuz reveals a fundamental weakness in the law of the sea: transit passage is strongly protected in doctrine but difficult to enforce in practice when a coastal State is willing to violate the rules. In that sense, the Strait is not only a strategic chokepoint — it is a stress test for the international legal order governing global commerce.

FEATURED IMAGE: The Strait of Hormuz connects the Gulf of Oman with the Persian Gulf in this photograph from the International Space Station as it orbited 262 miles above. In the right foreground, is the Soyuz MS-23 crew ship docked to the Prichal docking module. At bottom left, is a portion of the Northrop Grumman Cygnus space freighter and one of its cymbal-shaped UltraFlex solar arrays (photo: NASA)