The Strait of Hormuz is . Since the beginning of the conflict involving the United States, Israel and Iran on Feb. 28, 2026, oil tanker traffic through the world’s most critical oil shipping choke point has collapsed, .
Iran has threatened to , that pass through the strait from the oil depots of the Persian Gulf to the Arabian Sea and the rest of the world. Companies that insure ships against the risks of traveling in war zones are on an individual-ship basis. The international body that sets many shipping regulations has told ships’ crews that they have the into the area.
As of March 6, , without to move.
But . Most of the are those that operate outside the rules.
In maritime circles, these vessels are called the “.” They are vessels that ignore international restrictions on trade with certain countries, violate anti-pollution regulations, smuggle unauthorized goods or don’t want their cargo or activities too closely monitored.
They exist, even in a world filled with electronic tracking, because the world’s oceans aren’t governed the same way the land is. On land, armed personnel closely monitor carefully delineated borders, seeking to force everyone to follow clear rules. But at sea, regulation is almost the opposite. The system that governs international shipping is, at its foundation, voluntary.
The oceans run on trust
The tracking of ships is voluntary. The – signed by 167 countries – requires almost every commercial vessel to carry a , position, speed and heading to port authorities, coast guards and commercial tracking networks.
That international agreement, which is enforced by individual countries, requires ships to leave the transponders on and active. But there is no physical mechanism preventing a crew from switching it off or broadcasting a false position.
When a vessel turns off its transponder and goes dark, it doesn’t trigger an alarm at some global maritime headquarters. There is no such headquarters. The ship simply disappears from the map. Every map.
National jurisdiction is a matter of preference, not law. Every vessel sails under the flag of a nation, and that nation is theoretically responsible for regulating and inspecting it. But in practice, a ship’s registration in a particular country is a . Many law-abiding shipping companies , but this system leaves an opening for those who seek to skirt the rules.
A ship owned by a shell company in the United Arab Emirates can register under the flag of , , or any country that may lack the resources or the incentive to conduct real inspections. Even of oceangoing ships flying its flag.
When a vessel comes under scrutiny from port inspectors or coast guards, it can simply reregister under a different flag. Some registries even offer . If the new registration is fraudulent or the registry doesn’t actually exist, the vessel effectively .
Then there is insurance, which is the closest thing the maritime system has to a real enforcement mechanism. Mainstream insurers, , require vessels to meet safety standards, carry proper documentation and . A ship without insurance coverage cannot easily with reputable firms.Those restrictions are precisely what when war broke out.
But companies can avoid those rules, too. Two-thirds of ships carrying Russian oil – the by the U.S. – reportedly have , meaning nobody knows whom to call to cover the cleanup costs after a spill or collision. The enforcement mechanism works until ship owners realize they can just opt out of it entirely, using less reputable ports or transferring oil from ship to ship out at sea.
What opting out looks like
The results of this voluntary system can be surreal. In December 2025, , which was flying the flag of Guyana – even though . The vessel was, in legal terms, stateless, sailing under the authority of no nation on Earth.
Another vessel, the Arcusat, went further. found that , a unique seven-digit code assigned permanently to every ship. It is the maritime equivalent of scraping the VIN off a car.
Now layer these techniques together. An entity purchases an . It registers the ship through a , pays for a , carries opaque insurance and when approaching sensitive waters.
It loads sanctioned oil through a and delivers its cargo to a buyer who asks no questions. If the vessel attracts attention, it .
According to maritime intelligence firm Windward, approximately of all tankers carrying liquid cargo, which is primarily oil.
Why it matters now
The dark fleet did not emerge because the maritime system is broken. It emerged because the system is built on voluntary participation, all theoretically ensured by market forces.
For decades, the system worked not because it forced compliance but rather because opting out was more costly than opting in.
What changed is that international sanctions made compliance for some countries. A system built on voluntary participation, it turned out, could be voluntarily left.
If your national economy depends on oil exports, and the compliance system is preventing those exports, you build a parallel system. Iran began doing so , after sanctions were reimposed as part of negotiations over its nuclear development. in 2022 as restrictions hit in the wake of its invasion of Ukraine.
Now, with the Strait of Hormuz effectively closed to aboveboard maritime trade, the only vessels still moving are the ones that ignore the rules.
But the existence of the dark fleet doesn’t mean that the rules of the sea have failed. Rather, it reveals what kind of rules they always were. Illegal oil is the only oil moving in a crisis. In my view, that sends a message to those still playing by the rules: Opting out might be a viable option.
The opinions and views expressed are those of the author alone and do not necessarily represent those of the Department of the Navy or the U.S. Naval War College.
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