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3 things to know about naval blockades as U.S. begins patrols in the Strait of Hormuz
The U.S. Navy’s aircraft carrier USS Abraham Lincoln sails alongside guided-missile destroyer USS Frank E. Petersen Jr. and dry cargo ship USNS Carl Brashear in the Arabian Sea on Feb. 6.
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Days after the U.S. Navy began blockading the Strait of Hormuz, key questions remain unanswered about how such a large-scale operation can be sustained — and history suggests naval blockades are difficult to enforce and their results are often unpredictable at best.
The White House says it wants to choke off Iran’s main source of revenue, oil exports, by cutting the country off from global maritime trade. It’s a move aimed at increasing economic pressure on Iran after weeks of U.S. strikes have failed to persuade the country’s leaders to agree to end the war on Washington’s terms.
The U.S. Middle East command, known as CENTCOM, said on Sunday that it would intercept all vessels going to and from Iranian ports and will “not impede freedom of navigation” for ships from all other Persian Gulf ports.
Meanwhile, President Trump has made clear that stopping all shipping to and from Iran is aimed at strangling Iran’s ability to export petroleum. The administration labels the pressure tactic as a blockade — though Bryan Clark, a senior fellow at the Hudson Institute, argues it’s more of a naval quarantine, because “the U.S. is only stopping traffic that’s coming from Iran.”
Such a tactic is simply a new facet in the long-term sanctions that the U.S. has placed on Iran, says Eric Schuck, an economics professor at Linfield University in Oregon. He says the U.S. is following the classic economic pressure tactic aimed at breaking an enemy’s economy. The way to do that is finding and cutting off “something which is nonsubstitutable, something that is so essential to their economy that everything else is going to come to a halt.” In Iran’s case, that is oil.
But will the strategy work? Here are three lessons learned from the history of naval blockades.
Blockades zap resources and are hard to enforce
For much of history, naval blockades were mostly enforced through coordinated patrols, control of key routes and strategic positioning of ships. During the French Revolution and the Napoleonic wars of the early 19th century, for example, Britain imposed blockades on key French ports, which required a significant portion of the Royal Navy’s ships. And even then, some nimble French vessels — blockade runners — were still able to slip through the British screen.
Unlike the British squadrons off French ports or blockades during the 20th century, the U.S. Navy can use shipboard position beacons, satellites, drones and helicopters to locate and watch vessels coming in and out of the Strait of Hormuz, according to Steve Dunn, author of Blockade: Cruiser Warfare and the Starvation of Germany in World War One.
“Detection of vessels is much easier, with satellite, [planes and drones] and radar,” using helicopters and fast boats to send boarding parties to determine whether a ship will be allowed to pass, Dunn wrote in an email to NPR.
The Navy will likely need “six or so destroyers in rotation” to enforce the strait blockade, according to the Hudson Institute’s Clark, who is an expert in naval operations and electronic warfare. Prior to the U.S.-Iran war, an average of 138 ships passed through the strait daily. With so many vessels going through the strategic choke point, “it would be almost impossible [for the Navy] to keep up with that traffic volume,” he says.
The early months of the Ukraine war demonstrated a similar difficulty: Russia’s navy initially tried to restrict Ukrainian maritime exports from the Black Sea, using sea mines and warships to threaten commercial traffic. It resulted in a de facto partial blockade of Ukrainian grain exports, which are crucial to Ukraine’s economy. But it was “quite quickly negotiated away,” partly because Russia lacked the full military capacity needed to enforce it, according to Nicholas Mulder, a professor at Cornell University who specializes in the history of sanctions, blockades and economic warfare.
“That’s the difficult thing about blockades — you have to enforce them,” Mulder says.
The logistics of enforcing a blockade are not simple, Clark says. The blockading country’s navy must essentially pull over ships, like a traffic cop at sea. In the Arabian Sea outside the strait, the U.S. Navy “would intercept [ships] and basically get in their way and force them to turn … or take them over to a marshaling area or an anchorage in Oman,” he says.
The Navy isn’t prepared to track and stop that many ships, he says: “I don’t see the U.S. mounting a scorched-earth campaign of attacking every little vessel that tries to evade the blockade.”
They aren’t always effective
Schuck, of Linfield University, says during World War II, the Allied and Axis submarine campaigns — effectively naval blockades of shipping — provide a stark dichotomy of outcomes. The German U-boat campaign against Britain in the 1940s operated under the assumption that “if we sink everything, then it doesn’t matter. … We can cripple the British war economy,” Schuck says. However, in the end Britain was “able to make sure that the one supply line that mattered, that North Atlantic supply line,” remained open.
By contrast, the U.S. submarine campaign against Japan was “brutally effective,” targeting oil and resource flows from the Dutch East Indies to the Japanese home islands. The pressure forced Japan to shift its fleet in a way that undermined its own defense, since “they had to relocate a bunch of their fleet” just to defend their oil supply. As a result, things deteriorated on the homefront, Schuck says: By the closing months of the war, the caloric intake in Japan had dropped dramatically.
They don’t always hit their target
If history is any guide, naval blockades often have unintended consequences. “In most cases, what we’re aiming at and what we actually break are two different things,” says Schuck, who has studied the economics of naval blockades.
During World War I, the Allies imposed a naval blockade on Germany to restrict imports of strategic materials such as nitrates and phosphates used in explosives. However, these same chemicals were also critical for the production of fertilizer.
“What wound up breaking wasn’t so much the German defense industrial base — it was their agricultural sector,” Schuck says. As a result, Germany’s civilian population faced severe food shortages and widespread malnutrition in the latter years of the war.
Likewise, during the British blockade of French ports around the turn of the 19th century, French trade collapsed along with the economy.
In the case of Iran, Schuck says, its oil revenue is its lifeblood, so “there is a potential … that their food supply could be exposed from this.” But that likely depends on how long the blockade lasts or how effective it is at shutting down Iran’s commerce.
The US is planning to board and seize Iran-linked oil tankers and commercial ships in the coming days, according to a Saturday report by The Wall Street Journal.
The report noted that these actions would take place in international waters, potentially outside of the Middle East.
The US “will actively pursue any Iranian-flagged vessel or any vessel attempting to provide material support to Iran,” US Chairman of the Joint Chiefs of Staff Gen. Dan Caine said. “This includes dark fleet vessels carrying Iranian oil.”
“As most of you know, dark fleet vessels are those illicit or illegal ships evading international regulations, sanctions, or insurance requirements,” Caine continued.
Caine was further quoted as saying that the new campaign, which would be operated in part by the US Indo-Pacific Command, would be part of a broader US President Donald Trump-led campaign against Iran, known as “Economic Fury.”
White House spokeswoman Anna Kelly told the WSJ that Trump was “optimistic” that the new measures would lead to a peace deal.
The potential US military action comes as Iran tightens its grip on the Strait of Hormuz, including attacking several ships earlier on Saturday, the WSJ reported.
The report cited CENTCOM as saying that the US has already turned back 23 ships trying to leave Iranian ports since the start of its blockade on the Strait.
The expansion of naval action beyond the Middle East will provide the US with further leverage against Iran by allowing it to take control of a greater number of ships loaded with oil or weapons bound for Iran, the report noted.
“It’s a maximalist approach,” said associate professor of law at Emory University Law School Mark Nevitt. “If you want to put the screws down on Iran, you want to use every single legal authority you have to do that.”
Iran claimed earlier on Saturday that it had regained military control over the Strait, intending to hold it until the US guarantees full freedom of movement for ships traveling to and from Iran.
“As long as the United States does not ensure full freedom of navigation for vessels traveling to and from Iran, the situation in the Strait of Hormuz will remain tightly controlled,” the Iranian military stated.
In addition, Iranian Supreme Leader Mojtaba Khamenei declared on Saturday in an apparent message on his Telegram channel that the Iranian navy is prepared to inflict “new bitter defeats” on its enemies.
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April 18, 2026
A Pakistani Ranger walks past a billboard for the U.S.-Iran peace talks in Islamabad on April 12, 2026. The talks, led by Vice President JD Vance, produced no concrete movement toward a peace deal.
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Despite stalled talks with Iran and a fragile ceasefire nearing its end, President Trump expressed optimism this week that a permanent deal is within reach — one that may include Iran relinquishing its enriched uranium. However, experts who spent months negotiating a nuclear agreement during the Obama administration say mutual mistrust, starkly different negotiating styles make a quick truce unlikely.
Referring to Vice President Vance’s whirlwind negotiations in Islamabad last week that appear to have produced little beyond dashed expectations, Wendy Sherman, the lead U.S. negotiator on the Joint Comprehensive Plan of Action (JCPOA) nuclear deal finalized in 2015, says the administration’s approach was all wrong.
“You cannot do a negotiation with Iran in one day,” she told NPR’s Here & Now earlier this week. “You can’t even do it in a week.” To get agreement on the JCPOA, she said, it took “a good 18 months.”
The talks leading to that deal highlighted Iran’s meticulous style of negotiation, says Rob Malley, who was also part of the JCPOA negotiating team and later served as a special envoy to Iran under President Joe Biden.
Summing up the two sides’ differing styles, Malley said: “Trump is impulsive and temperamental; Iran’s leadership [is] stubborn and tenacious.”
U.S. Secretary of State John Kerry speaks during a news conference on the Iran nuclear talks deal at the Austria International Centre in Vienna, Austria on July 14, 2015.
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In 2015, patience led to a deal
The talks in 2015, led by Secretary of State John Kerry and Iran’s Foreign Minister Mohammad Javad Zarif, culminated with a marathon 19-day session in Vienna to finish the deal, says Jon Finer, a former U.S. deputy national security adviser in the Biden administration. Finer was involved in the negotiations as Kerry’s chief of staff. He said his boss’s patience “was a huge asset” in getting the deal to the finish line, he said.
Mohammad Javad Zarif, Iran’s foreign minister during the negotiations for the Obama-era nuclear deal, speaks on April 22, 2016 in New York.
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“He would endure lectures … ‘let me tell you about 5,000 years of Iranian civilization’… and just keep plowing ahead,” Finer said, adding that a tactic of Iranian negotiators seemed to be “to say no to everything and see what actually matters” to the U.S.
“They’re just maddeningly difficult,” he said. “You need to go back at the same issue 10 or 12 times over weeks or months to make any progress.”
Even so, Finer called the Iranian negotiators “extremely capable” — noting that, unlike the U.S., they often lacked expert advisers “just outside the room,” yet still mastered the details of nuclear weapons, nuclear materials and U.S. sanctions.
“They were also negotiating not in their first language,” Finer added. “The documents were all negotiated in English, and they were hundreds of pages long with detailed annexes.”
Vance’s trip to Islamabad suggests that the U.S. doesn’t have the patience for a negotiation to end the conflict that could be at least as complex and time-consuming. “The Trump administration came in with maximalist demands and actually just wanted Iran to capitulate,” Sherman, who served as deputy secretary of state during the Biden administration, told Here & Now. “No nation – even one as odious as the Iran regime – is going to capitulate.”
Distrust but verify
Iran was attacked twice in the past year. First in June of last year, as nuclear negotiations were ongoing, Israel and the U.S. struck the country’s nuclear facilities. Months later, at the end of February, Iran was attacked again at the start of the latest conflict. This time around, “the level of trust is probably almost at an all-time low,” Malley said.
“It’s hard for them to take at their word what they’re hearing from U.S. officials,” Malley said. The Iranians, he said, have to be wondering how long any commitment will last and “will be very hesitant to give up something that’s tangible” – such as their enriched uranium – in exchange for anything that isn’t ironclad or subject to suddenly be discarded by Trump or some future president.
“Once they give up their stockpile … they can’t recapture it the next day,” Malley said.
Even during the 2013-2015 nuclear deal talks, the decades of mistrust between Tehran and Washington were impossible to ignore, Finer said. “Our theory was not trust but verify — it was distrust but verify,” he said, adding: “I think that was their theory too.”
Malley cautions about relying on the JCPOA as a guide to how peace talks to end the current war might go. The leadership in Tehran that agreed to the deal is now gone — killed in Israeli airstrikes, he says. The regime’s military capabilities are also greatly diminished and “whatever lessons were learned in the past … have to be viewed with a lot of caution, because so much has changed,” he said.
Negotiations have a leveling effect
Mark Freeman, executive director of the Institute for Integrated Transitions, a peace and security think tank based in Spain that advises on conflict negotiations, says several factors shape the U.S.-Iran relationship. Going into talks, one side always has the upper hand, he says, but negotiations have a leveling effect. “The weaker party gains just by virtue of entering into a negotiation process,” he said.
Each side is looking for leverage, he adds.
In Iran’s case, it has used its closure of the Strait of Hormuz to exert such leverage, while the White House has shown an eagerness to resolve the conflict quickly. “If one side perceives the other needs an agreement more … that shapes the entire negotiation,” he said.
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