One month into his war on Iran, U.S. President Donald Trump is now scrambling to secure something that was not previously insecure—the Strait of Hormuz—turning it into the central thrust of the war’s uncertain endgame.

Iran, or more specifically its Islamic Revolutionary Guard Corps (IRGC), has taken effective control of the world’s most important shipping lane and choke point, through which normally passes one-fifth of the world’s oil and natural gas as well as even more of its fertilizer and helium. 

One month into his war on Iran, U.S. President Donald Trump is now scrambling to secure something that was not previously insecure—the Strait of Hormuz—turning it into the central thrust of the war’s uncertain endgame.

Iran, or more specifically its Islamic Revolutionary Guard Corps (IRGC), has taken effective control of the world’s most important shipping lane and choke point, through which normally passes one-fifth of the world’s oil and natural gas as well as even more of its fertilizer and helium. 

Iran has threatened for decades to close the strait, and U.S. war planners have spent decades preparing for just that—and yet it is effectively closed. Tanker transits during the entire month of March don’t add up to what used to pass through each day. Oil prices climbed again early on Thursday, reaching more than $107 a barrel as the accumulated impact of millions of barrels of lost crude shipments start to be felt by a global economy that burns more than 100 million barrels of the stuff every day.

What’s interesting about Iran’s chokehold on Hormuz is how different it is from the paralysis that the Iran-backed Houthis inflicted on shipping traffic in the Red Sea between 2023 and 2025. The Houthis attacked ships and scared them into taking alternate routes, and traffic has never recovered. (The Houthis could still come into this war; they haven’t yet, but if they do, the one major alternative for Saudi oil exports will be curtailed, with even more disastrous impacts on oil markets.) Iran has attacked some ships—around 16 so far—which is why shipowners are reluctant to risk the passage, and why maritime insurance rates have soared. 

But that is not Iran’s ultimate vision for control of the Strait of Hormuz.

Since mid-March, Iran has turned the Strait of Hormuz into a “toll booth,” according to Lloyd’s List Intelligence, a major maritime news and analysis firm—rerouting ships from the normal, well-demarcated two-way lane in the middle of the strait to an alternate path close to the Iranian coastline, between the islands of Qeshm and Larak. The IRGC checks ships’ nationality, ownership, cargo, and crew, and if it grants permission, then those ships can pass out of the strait. Lloyd’s List estimates that some two dozen have used that route so far. 

Some have even had to pay for the privilege—at least two so far, according to Lloyd’s, with estimated tolls at $2 million per transit. Others, such as Indian tankers full of cooking gas, got free passage as a diplomatic measure, and ships exporting Iranian oil don’t have any trouble at all.

It’s early days, and only a couple dozen ships have taken the alternate route to get out—and fewer have paid—but that could become the new normal.

“Of course it’s possible Iran could turn it into a toll booth, just from an operational and technical level, if countries are willing to pay. I have a hard time believing the United States would abide that,” said Josh Lipsky, the senior director of the Geoeconomics Center at the Atlantic Council.

Even more ships might be paying. Lipsky and his team have seen a notable uptick in transactions on China’s alternate payment system—CIPS—which tracks with reports of Iran’s demand for oil payments (and tolls) to be settled in yuan. CIPS transactions are consistently high this March and higher than at any point in the past year.

Iran made clear its new vision for management of the strait in a letterto the International Maritime Organization earlier this week, when it said that ships from “non-hostile” countries could pass through the narrow waterway, provided that they comply with Iranian demands. Iran is liking the notion so much that turning the Strait of Hormuz into a Suez Canal-style cash machine has become one of its demands in preliminary talks with the United States.

Restricting passage through an international strait goes against international law—the U.N. Convention on the Law of the Sea is quite clear about that—but although Iran signed the treaty, it never ratified it (much like the United States). 

“This is all illegal,” Lipsky said.

Beyond the abstractions of international law, there are concrete laws that shipowners are worried about when it comes to Iran’s new toll booth, Lloyd’s noted. Paying money to Iran could run afoul of U.S. sanctions, both in the oil sector and by providing material support to a foreign terrorist organization (as the United States has designated the IRGC). The United Kingdom and the European Union also have sanctions on that sort of thing, which makes most shipping lines reluctant to lean into Iran’s new Q-route. (A Q-route is a safe route through a minefield or other proscribed passage.)

With the Strait of Hormuz having become the focus of Trump’s Iran war, even more geography lessons loom. First, and for decades, Trump had his eyes on Iran’s Kharg Island, which handles about 90 percent of Tehran’s oil exports. Now, though, attention is shifting to a handful of other islands closer to the strait itself: Greater Tunb, Lesser Tunb, Abu Musa, and Larak. (The Tunbs and Abu Musa are occupied by Iran but are claimed by the United Arab Emirates in what has been a decades-long territorial dispute.)

Those islands are becoming increasingly relevant not just because they sit astride the passage, but also because U.S. Marines will arrive in the region starting as soon as March 27. The USS Tripoli, with about 2,200 Marines, will be first on station, followed early next month by the USS Boxer with another expeditionary force. Axios reports that those little islands are displacing Kharg as a potential objective of the Trump administration’s “final blow” to open the strait and finish the war.

And while Israel claimed on Thursday to have killed the IRGC commander responsible for operations in the Strait of Hormuz, Iran has shown in the past year an increasing decentralization of its military command and control. The regime has spent 40 years preparing for operations in the strait, including with missiles, mines, small boats, and drones, and has an asymmetric advantage, especially against a U.S. opponent with a shrinking navy with no minesweepers currently in the region. 

Iran has spent decades threatening to use the leverage of its potential dominance over the world’s most vulnerable choke point, and now it has leveraged it and discovered a potentially lucrative way to take advantage of that, even if it is at odds with international law. 

Unless and until the United States—and any allies that eventually join—pry open the strait, by diplomacy or by force, Iran’s newfound leverage will be the new normal. That’s quite a legacy for a four-week war.