Naval

The Strait of Hormuz, a narrow waterway once carrying roughly a fifth of the world’s oil and gas, remains effectively closed after the United States and Iran imposed competing blockades.

Naval blockades are one of the oldest weapons in warfare, requiring no ground troops or invasion, just the ability to cut off what an enemy needs to survive. These blockades have reshaped economies, societies and alliances across generations, sometimes with instant shockwaves, sometimes with effects only seen later.

From Israel’s ongoing siege of the Gaza Strip to blockades during World War I, here are some notable naval blockades in modern history:

Israel’s siege of Gaza (2007-present)

Israel’s complete land, sea and air blockade of the Gaza Strip is one of the longest sieges in modern history.

Launched in 2007, Israel has limited the entry of goods and essential supplies, causing a prolonged humanitarian and economic crisis for the Strip’s 2.3 million people, who cannot travel freely.

Before Israel’s genocidal war on Gaza began in October 2023, fishermen were restricted to 6-15 nautical miles (11-28km) from shore, well below the 20-nautical-mile (37km) zone guaranteed by the Oslo Accords.

After 2023, with Israel’s policy of starving the population, fishermen have taken extreme measures to feed their families, leading to many being killed by Israeli fire.

Since 2008, several Freedom Flotilla vessels have attempted to break the Israeli blockade. Since 2010, all flotillas attempting to break the Gaza blockade have been intercepted or attacked by Israel in international waters.

On April 30, Israel raided 22 out of the 58 vessels in the most recent Global Sumud Flotilla campaign in international waters more than 1,000km (620 miles) from Gaza.

Blockade of Biafra (1967-70)

During the Nigerian Civil War, which began in July 1967, the Nigerian federal government imposed a land, sea and air blockade on the secessionist Republic of Biafra shortly after it declared independence.

The blockade led to widespread starvation, widely seen as a deliberate wartime strategy, transforming a territorial conflict into a global humanitarian crisis. Death tolls vary, but it is estimated that one to two million people died, the vast majority from hunger and disease rather than direct conflict.

The nearly three-year-long blockade ended with the Biafran surrender in January 1970.

Beira Patrol blockade (1966-75):

The Beira Patrol was a nine-year-long blockade by the British navy to prevent oil from reaching Rhodesia, present-day Zimbabwe, through the Mozambican port of Beira, enforced under United Nations sanctions following Rhodesia’s unilateral declaration of independence.

The blockade largely failed its strategic goal. Rhodesia continued receiving oil via South Africa and other Mozambican ports, which the UN resolution did not authorise the British navy to intercept.

Additionally, the cost to the United Kingdom was substantial. The operation tied up 76 naval ships over nine years, with two frigates required on station at all times.

The blockade ended in July 1975, when Mozambique’s newly gained independence from Portugal allowed it to credibly commit to blocking oil transit to Rhodesia, rendering the naval patrol redundant.

Cuban Missile Crisis ‘quarantine’ (1962)

In October 1962, the US ordered a naval “quarantine” of Cuba after US U-2 spy planes discovered Soviet nuclear missile sites under construction on the island.

The US deliberately called it a “quarantine” rather than a blockade, which would have been legally an act of war, aiming to prevent the Soviets from bringing in more military supplies and to pressure them to remove the missiles already there.

The quarantine drew a line 500 nautical miles (920km) from Cuba’s coast, with US warships authorised to stop, search, and turn back any vessel carrying offensive weapons if necessary.

The crisis brought the world to the brink of nuclear war. The then-Soviet First Secretary Nikita Khrushchev called the blockade “outright piracy” and an act of aggression, and initially ordered ships to proceed. For several days, Soviet vessels steamed towards the quarantine line as the world watched.

The most dangerous phase of the standoff lasted 13 days. An agreement was reached in which the Soviets would dismantle their offensive weapons in Cuba in exchange for a US public declaration not to invade Cuba, and a secret agreement to remove US Jupiter missiles from Turkiye.

The naval quarantine was formally ended on November 20, 1962, after all offensive missiles and bombers had been withdrawn.

Blockade of Wonsan (1951-53)

During the Korean War, UN naval forces led by the US imposed a blockade of the North Korean port of Wonsan in February 1951, lasting nearly two and a half years.

It aimed to deny the North Korean navy access to the city, which was strategically significant for its large harbour, airfield and petroleum refinery.

The blockade was preceded by a dangerous mine-clearance operation in October 1950. North Korean forces had been well supplied by the Soviet Union and China with sea mines, and during the clearance, the sweepers USS Pledge and USS Pirate were sunk, killing 12 men and wounding dozens.

The operation successfully constrained North Korean and Chinese forces on the east coast, forcing them to divert thousands of troops and artillery pieces away from the front line. UN forces also captured several harbour islands, which strengthened the blockade’s grip on the port.

The blockade ended after 861 days with the signing of the Korean Armistice Agreement in July 1953. By that point, allied naval fire had almost levelled Wonsan.

US submarine blockade of Japan (1942-45)

The US imposed a submarine blockade against Japan during the Pacific War.

The blockade began taking shape in 1942, combining US naval submarine attacks on merchant shipping with minelaying operations to cripple Japan’s war capabilities, disrupt shipping and cut off vital supplies such as food and fuel.

As an island nation, Japan was especially vulnerable, almost entirely dependent on imports of oil, rubber and raw materials. Its economy and military could not function without open sea lanes.

Over the course of the war, US submarines sank some 1,300 Japanese merchant ships and roughly 200 warships. By 1945, oil imports had effectively ceased.

Food imports collapsed, causing significant shortages and malnutrition across Japan by 1945, though the extent of civilian starvation is disputed.

After the US dropped atomic bombs on Hiroshima on August 6 and Nagasaki on August 9, 1945, Japan announced its surrender on August 15, bringing the blockade and the Pacific War to an end.

Blockade of eastern Mediterranean (1915-18)

In August 1915, during World War I, the Allied forces imposed a blockade of the eastern coast of the Mediterranean to cut off military supplies and weaken the Ottoman Empire’s war effort.

The declared area ran from the intersection of the Aegean Sea and the Mediterranean Sea in the north to the Egyptian frontier in the south. The blockade was initiated by Britain and France, later assisted by Italy and other Allied powers.

The consequences were devastating. Military supplies, munitions, oil, food and medicine were all targeted. The food crisis was compounded by a locust plague in 1915 and a severe drought, contributing to severe famine across Lebanon and Greater Syria.

Reports suggest the famine led to 500,000 deaths by 1918, mostly civilians, with Mount Lebanon losing an estimated one-third of its population. Mass migration followed.

The blockade remained in place throughout the war and lifted only when Allied forces occupied Beirut and Mount Lebanon in October 1918.

Allied blockade of Germany (1914-19)

The British navy began blockading Germany almost immediately after the outbreak of the war in August 1914.

The naval blockade extended from the English Channel to Norway, cutting off Germany from the oceans.

Britain mined international waters to prevent ships from entering the ocean, creating danger even for neutral vessels.

Germany responded by declaring the seas around the British Isles a “military area”, prompting Britain and France to ban all goods to and from Germany.

The blockade’s most devastating consequence was famine. The winter of 1916-17, known as the Turnip Winter, marked one of the harshest years in wartime Germany.

The blockade had cut off food and fertiliser imports, a failed potato harvest left little to fall back on, and a breakdown in food distribution compounded the crisis. It is estimated that between 424,000 and 763,000 civilians died from diseases related to hunger and malnutrition.

The blockade was not yet fully lifted until July 1919, after the Treaty of Versailles had been signed.

May 1 (Asia Today) — Japan considered deploying its Self-Defense Forces to the Strait of Hormuz ahead of a summit with U.S. President Donald Trump but ultimately held back due to constitutional and legal constraints, reports said Friday.

Prime Minister Sanae Takaichi reviewed options in March to send naval assets to the region amid heightened tensions in the Middle East, according to Japanese media.

Two proposals were examined: dispatching minesweepers under Japan’s Self-Defense Forces law or sending destroyers and patrol aircraft for “survey and research” purposes under a separate legal framework. Both options were shelved due to concerns they could violate Japan’s pacifist constitution.

Article 9 of Japan’s constitution renounces war and prohibits the use of force to settle international disputes, placing strict limits on overseas military operations.

The discussions were prompted in part by U.S. requests for allied support in securing maritime routes. Trump warned in March that Iran could disrupt shipping in the Strait of Hormuz using drones, mines and short-range missiles, and called on countries including Japan, South Korea and European allies to contribute naval forces.

The Strait of Hormuz is a critical energy corridor for Japan, which depends heavily on Middle Eastern oil imports. Any prolonged disruption could affect supplies of crude oil, naphtha and petrochemical products.

Japanese officials acknowledged the urgency of ensuring maritime security but stressed legal limits. Defense Minister Shinjiro Koizumi said Japan must act within the bounds of its laws, while Takaichi told parliament she had explained constitutional constraints during talks with Trump.

Legal concerns centered on whether minesweeping operations in a conflict zone could be considered part of combat activities, potentially violating Article 9. Similarly, deploying naval vessels under the guise of research could be viewed as de facto joint operations with U.S. forces in a high-risk area.

Despite the decision, debate continues within Japan. Lawmakers from the ruling Liberal Democratic Party have suggested revisiting deployment options if maritime disruptions persist, emphasizing the importance of securing sea lanes.

The episode highlights Japan’s evolving security posture. While Tokyo has expanded defense spending and strengthened alliances, its ability to deploy forces abroad remains constrained by constitutional interpretation.

The issue also carries implications for South Korea, which relies on the same energy routes. If the United States increases pressure on allies to contribute to maritime security, both Seoul and Tokyo may face similar dilemmas balancing energy security with military involvement.

— Reported by Asia Today; translated by UPI

© Asia Today. Unauthorized reproduction or redistribution prohibited.

Original Korean report: https://www.asiatoday.co.kr/kn/view.php?key=20260501010000010

On March 11, the Thai cargo ship Mayuree Naree was struck by two projectiles while crossing the Strait of Hormuz, one of the world’s most important waterways located between Iran and Oman. A fire broke out in the engine room, and while 20 sailors were rescued, three remained trapped inside the stricken vessel. Their remains were found weeks later when a specialised rescue team boarded the vessel, which had run aground on the shores of Iran’s Qeshm island.

At about the same time, a “shadow fleet” of tankers continued to navigate the very same waters safely. Operating with fake flags, disabled signals and unspecified destinations, this covert armada survived because it operates outside the traditional rules of maritime trade.

Iran threatened to block “enemy” ships passing through the Strait of Hormuz – a crucial chokepoint for a fifth of the world’s oil – in the wake of the United States-Israeli war launched on February 28. Soon, navigation through the strait was disrupted amid fears of attacks.

Following a temporary ceasefire on April 8, the United States imposed a full naval blockade on Iranian ports on April 13. Theoretically, traffic through the strait should have come to a complete halt.

However, tracking data reveals a remarkably different reality.

An exclusive Al Jazeera open-source investigation tracked 202 voyages made by 185 vessels through the strait between March 1 and April 15, navigating both under fire and across blockade lines.

The numbers behind the shadows

To understand how the strait operated under extreme pressure, Al Jazeera’s Digital Investigative Unit monitored the waterway daily, cross-referencing vessel International Maritime Organization (IMO) numbers with international sanction lists from the US Office of Foreign Assets Control (OFAC), the European Union, the United Kingdom and the United Nations. An IMO number is a unique seven-digit figure assigned to commercial ships.

Of the tracked voyages, 77 (38.5 percent) were directly or indirectly linked to Iran. Notably, 61 of the ships transiting the strait were explicitly listed on international sanctions lists.

The investigation divided the conflict into three distinct phases to map the fleet’s behaviour:

• Phase 1: Open War (March 1 – April 6): 126 ships crossed the strait, peaking at 30 vessels on March 1. Among these, 46 were linked to Iran.
• Phase 2: The Truce (April 7 – 13): 49 ships crossed during this fragile pause. More than 40 percent of these vessels were tied to Iran, including the US-sanctioned, Iranian-flagged Roshak, which successfully exited the Gulf.
• Phase 3: The US Blockade (April 13 – 15): Despite the explicit naval blockade, 25 ships crossed the strait.

Breaking the blockade

When the US blockade took effect, the shadow fleet adapted immediately.

The Iranian cargo ship “13448” successfully broke the blockade. Because it is a smaller vessel operating in coastal waters, it lacks an official IMO number, allowing it to evade traditional sanction-monitoring tools. The vessel departed Iran’s Al Hamriya port and reached Karachi, Pakistan.

Similarly, the Panama-flagged Manali broke the blockade, crossing on April 14 and penetrating the cordon again on April 17 en route to Mumbai, India.

The investigation uncovered widespread manipulation of Automatic Identification System (AIS) trackers. Vessels such as the US-sanctioned Flora, Genoa and Skywave deliberately disabled or jammed their signals to hide their identities and destinations.

Fake flags and shell companies

To obscure ultimate ownership, the shadow fleet heavily relies on a complex web of “false flags” and shell companies. The investigation identified 16 ships operating under fake flags, including registries from landlocked nations like Botswana and San Marino, as well as others from Madagascar, Guinea, Haiti and Comoros.

The operational network managing these ships spans the globe. Operating firms were primarily based in Iran (15.7 percent), China (13 percent), Greece (more than 11 percent) and the United Arab Emirates (9.7 percent). Notably, the operators of nearly 19 percent of the observed vessels remain unknown.

The toll of a parallel system

Despite the intense military pressure, energy carriers dominated the traffic, with 68 ships (36.2 percent) transporting crude oil, petroleum products and gas. Ten of these tankers were directly linked to Iran. Non-oil trade also persisted, with 57 bulk and general cargo ships crossing during the open war phase, 41 of which were tied to Tehran.

Before the war, at least 100 ships crossed the Strait of Hormuz daily. Today, a staggering 20,000 sailors are trapped on 2,000 ships across the Gulf – a crisis the International Maritime Organization described as unprecedented since World War II.

A shadow Iranian fleet, meanwhile, has been navigating seamlessly as part of a parallel maritime system born from 47 years of US sanctions on Tehran. Washington slapped sanctions on Tehran following the 1979 Islamic revolution that toppled the pro-Washington ruler Shah Mohammad Reza Pahlavi. The two countries have had no diplomatic ties since 1980.

On the same day that the Chief of Naval Operations answered our question about the future of the F/A-XX sixth-generation naval fighter program, stating a final selection between the offerings from Boeing and Northrop Grumman will be coming in August, the latter of the two firms has released a new teaser video. Previously, we only had one rendering of Northrop’s notional F/A-XX concept. Now we have a more detailed panning video and a new head-on perspective view.

The video clip, posted on Northrop Grumman’s X account this evening, as seen below, states: “We’re bringing tomorrow’s horizon into focus, faster, stronger, and ready when the warfighter needs it.”

What we see in the clip is the same general design we saw in the still image earlier, but much more of it. This includes a head-on shot, showing the aircraft’s stealthy and efficient tailless design and rear-set dorsal inlets, as well as its very broad nose and canopy.

The aircraft in the new stylized video clip has some interesting proportions. The size of the landing gear and especially the canopy give it something of a smaller overall appearance than what one would expect from a heavy sixth-generation naval fighter that will be stuffed with fuel and weapons. Of course, this could be due to the somewhat ‘cartoonish’ nature of this new glitzy clip, and how accurate this rendering is to the actual Northrop Grumman F/A-XX is still unknown. At the very least, some of the aircraft’s features (such as its inlets) will have been significantly changed for security issues pertaining to its sensitive design elements.

We also see the wings, which look like they have a bit of camber on the outer sections and possibly a bit of ‘crank’ too. We also see the wings folded in the first part of the clip.

What could be a weapons bay with its doors open is also visible in some of the angles seen in the clip. At first glance, this appeared to be for the jet’s very stout-looking landing gear, but they are curved inward. There are additional doors on the centerline, as well, pointing to two separate bays.

Overall, because of the size of the canopy, it is hard to tell if this is a single-seat or a two-crew aircraft. The canopy is so large in these renders that a side-by-side crew arrangement may even be possible, although that seems unlikely.

Once again, we don’t know how close this computer-generated model is to the real thing, but considering this aircraft will have to carry a sizable weapons load and have something approaching a combat radius of 1,000-miles, while still fitting well within the confines of a supercarrier, it should be firmly in the heavy fighter class.

Maybe Northrop Grumman will share more on its F/A-XX at the annual Sea-Air-Space convention in Washington this week, and we will be ready to report it from the scene if they do.

We have reached out to Northrop Grumman with questions, and we will update this post if we hear back.

Contact the author: Tyler@twz.com

Northrop Grumman CEO Kathy Warden says she is confident in her company’s ability to deliver next-generation carrier-based fighters to the U.S. Navy if it is picked as the winner of the F/A-XX competition. The U.S. Navy’s top officer said yesterday that the goal was to award the F/A-XX contract by August of this year, but also that one unnamed contractor in the running “really can’t deliver in the timeframe we need it.”

Chief of Naval Operations (CNO) Adm. Daryl Caudle offered his latest comments on F/A-XX yesterday in response to a direct question from TWZ at a roundtable on the sidelines of the Navy League’s Sea-Air-Space 2026 exposition. The Pentagon had tried to put the Navy’s future fighter ambitions on hold last year, arguing that the U.S. industrial base did not have sufficient capacity to support work on two sixth-generation combat jets simultaneously. Boeing won the contract to build what is now called the F-47 for the U.S. Air Force in March 2025. Boeing is the only other company known to be in the running now for F/A-XX. Last year, it was reported that Lockheed Martin had been eliminated from the competition.

Late yesterday, Northrop Grumman also released a new computer-generated F/A-XX promotional video, seen below. You can read our analysis of what is seen therein here.

“We do expect the Department [of the Navy] to make an award selection in the third quarter,” Northrop Grumman’s Warden said during a routine earning call today in response to a direct question about Adm. Caudle’s remarks. “We are confident in our ability to deliver our solution to the Navy.”

She did not explicitly confirm or deny that the CNO had been referring to Northrop Grumman when he mentioned a contractor’s inability to meet the Navy’s schedule needs on F/A-XX.

“We and our suppliers are prepared to bring the workforce and infrastructure that’s needed to execute the program, and our track record on B-21 demonstrates that ability to deliver a complex aircraft on schedule,” Warden added. “Regarding the financials, we’d expect upside to the sales and earnings from our current guidance, if we are entrusted to build the F/A-XX, and it would be a top priority for our company to do so.”

Air Force officials, as well as members of Congress, regularly describe the B-21 Raider bomber as a model acquisition program that has been able to keep on schedule and budget despite at least some hurdles along the way. Earlier this year, Northrop Grumman reached an agreement with the Air Force to accelerate B-21 production.

It’s also worth remembering that Northrop Grumman withdrew in 2023 from the Air Force competition that would lead to the F-47. The company framed the decision at the time as a voluntary one.

“I’ll just say that, when I noted we have other opportunities we are pursuing, I won’t disclose at this point exactly what those are until a little more information comes out,” Warden, who was also CEO at that time, said when announcing the withdrawal, which was widely seen as a reference to F/A-XX. “You could assume that if we feel we’re well-positioned, and the government is appropriately balancing risk and reward, as I said that that would be a program we would pursue.”

Former top Air Force officials subsequently said that Northrop Grumman’s bid had been on the verge of getting cut.

As mentioned, industrial base capacity questions have swirled around F/A-XX. The Pentagon had tried to effectively shelve the Navy’s next-generation fighter program in its proposed budget for the 2026 Fiscal Year. At the time, a senior U.S. defense official explicitly said that the decision was “due to our belief that the industrial base can only handle going fast on one program at this time, and the presidential priority to go all in on F-47, and get that program right.”

Congress later intervened to appropriate some $1.69 billion in funding to keep F/A-XX moving ahead in the 2026 Fiscal Year.

“I will tell you, we, Northrop Grumman, are ready to execute F/A-XX,” Tom Jones, President of Northrop Grumman’s Aeronautics Systems sector, had also told TWZ and other outlets in response to a question about industrial base capacity in relation to the program back in December. “We’re looking to try and make sure that the customer community knows that we believe that we’re ready to go and we can execute it.”

Boeing Defense and Space CEO Steve Parker had also pushed back on the assertion that the U.S. industrial base could not support F-47 and F/A-XX at the same time last year. The company’s pitch for the Navy’s program appears to be a navalized adaptation of the F-47.

“The Air Force has got a lot of demand on the system. The Navy’s got a lot of demand,” Adm. Caudle had also said yesterday. “So there was, you know, a check twice, cut once, kind of mentality here on this decision. And now there, I think we’re all on the same page on the reason why the hard look needed to be done. I’m good with it.”

Questions about the overall future of F/A-XX do remain, despite clear support from top Navy leaders like Caudle and Congress. The Navy looks set to request just over $140 million for the program in Fiscal Year 2027. This is a very meager sum, especially for a program of this magnitude. In contrast, the Air Force is seeking $5 billion in additional funding for F-47. Billions of dollars have already been appropriated for the Air Force’s next-generation fighter effort.

The Pentagon and the individual services are rolling out more details about their annual budget proposals today, which could offer more insights into the plans now for F/A-XX in the coming years. Securing the contract to build the Navy’s next-generation fighter is still likely to be an important win for whichever company the service selects in the end.

UPDATE: 4/22/2026 –

The U.S. Navy has issued a statement regarding Adm. Caudle’s comments earlier this week, which is as follows:

“During a question-and-answer session at the Sea-Air-Space Exposition, Chief of Naval Operations Admiral Daryl Caudle was asked about the Navy’s sixth-generation strike fighter program (F/A-XX). Adm. Caudle emphasized that the Navy’s priority is ensuring through due diligence the selected vendor can deliver the required capability on the timeline needed by the fleet while also considering broader industrial base capacity. Any reference to ‘a specific offeror’ was intended as a general anecdotal comment and was not directed at any vendors currently under consideration.”

Contact the author: joe@twz.com

WASHINGTON — President Trump has turned to naval blockades to pressure the governments of Venezuela, Cuba and now Iran to meet his demands, but his preferred tactic is confronting a very different reality in the Middle East than in the Caribbean.

Unlike Cuba or Venezuela, Iran choked off a crucial trade route for energy shipments, meaning the longer the standoff persists, the more the global economy will suffer. Tehran also poses a greater military threat than those two adversaries in America’s own hemisphere and requires a sustained military presence far from U.S. shores.

Iran’s leverage over the Strait of Hormuz gives it power during a shaky ceasefire because the widening economic risks, especially higher U.S. gas prices in an election year, could force the Republican president to end the blockade on Iran’s ports and coastline, experts say.

“It’s really a question now of which country, the U.S. or Iran, has a greater pain tolerance,” said Max Boot, a military historian and senior fellow for national security studies at the Council on Foreign Relations.

Iran presents ‘major differences’ from other blockades

The effectiveness of Trump’s use of the world’s most powerful navy to block the trade of Iran’s sanctioned oil and other goods is very much up for debate. But it certainly appears to be intensifying as the war grinds on.

The U.S. military on Thursday announced the seizure of another tanker associated with the smuggling of Iranian oil, a day after Iran’s paramilitary Revolutionary Guards took control of two vessels in the crucial waterway.

Trump also announced he has ordered the U.S. military to “shoot and kill” Iranian small boats laying sea mines in the strait.

But the situation in Iran is not exactly analogous to what is playing out with the U.S. operations in Venezuela and Cuba.

Some experts say Trump’s success in Venezuela probably had more to do with the U.S. military raid that captured leader Nicolás Maduro than American warships seizing sanctioned oil tankers to enforce U.S. control over the South American country.

A U.S. oil embargo on Cuba, meanwhile, has caused the island’s most severe economic crisis in decades. While U.S. and Cuban officials have met recently on the island for rare talks, the financial strangulation has failed to produce the Trump administration’s stated goal of leadership change.

“I do think that the success of the Maduro mission in Venezuela has probably emboldened the president,” said Todd Huntley, director of Georgetown University’s National Security Law Program.

That does not make the situations in Venezuela and Iran similar — geographically, militarily or politically. “There are some major differences,” said Huntley, a retired Navy captain and judge advocate general.

While the blockade against Iran has delivered a severe blow to its economy, including stopping freighters from importing various supplies, the country has still been able to move some of its sanctioned oil, ship-tracking companies say.

Iran has rejected Trump’s demands to reopen the strait, where 20% of the world’s oil normally flows, and it has been firing on ships again this week. Stalled shipments through the strait have sent gasoline prices skyrocketing far beyond the region and raised the cost of food and a wide array of other products, creating a political problem for Trump before the November’s elections.

“Blockades are usually just one tool of a mechanism used in a conflict,” said Salvatore Mercogliano, a maritime history professor at Campbell University in North Carolina. “They can be important. But it’s only one element. And I don’t think it’s going to be enough to convince the Iranians.”

Effectiveness of U.S. blockade called into question

Adm. Brad Cooper, head of U.S. Central Command, claimed last week that “no ship has evaded U.S. forces.” The command overseeing the Middle East said it has directed 31 ships to turn around or return to port as of Wednesday.

Merchant shipping groups are skeptical.

Lloyd’s List Intelligence said “a steady flow of shadow fleet traffic” has passed in and out of the Persian Gulf, including 11 tankers with Iranian cargo that have left the Gulf of Oman outside the strait since April 13.

The maritime intelligence firm Windward said this week that Iranian traffic continues to flow “via deception.”

Iranian ships have several ways to sneak through the blockade, including spoofing their location tracking data or traveling through Pakistani territorial waters, Mercogliano said. He also noted that the sheer volume of shipping traffic the military needs to screen is a challenging task.

Blockades require patience to work

The last time the U.S. mounted a blockade similar to the one focused on Iranian ships was during the Kennedy administration in the early 1960s, against Cuba, Huntley said.

“And it wasn’t even called a blockade,” he said. “We called it quarantine.”

Some naval blockades over the course of history have had an impact, such as Britain’s blockade on Germany during World War I. “But they tend to be very long-term impacts, whereas Trump is looking for short-term, quick results,” according to Boot, the military historian.

He said Trump probably saw the blockade on sanctioned oil tankers tied to Venezuela as playing a large role in the success of leadership changes in that country. But Boot said it had more to do with the U.S. ousting Maduro and the subsequent cooperation from his vice president, Delcy Rodríguez, who is now the acting president.

“There is no Delcy Rodríguez in Cuba or Iran,” Boot said. “I think his success in Venezuela led him astray, thinking that this was a template that could be replicated elsewhere. He sees it as a huge success at little cost. And, in fact, it turns out to be a unique set of circumstances.”

Finley, Klepper and Toropin write for the Associated Press.