The US Navy is set for a confrontation with the Islamic Revolutionary Guard Corps' so-called speedboat swarms as it tries to blockade the Strait of Hormuz within hours. 

Although Washington has dealt a severe blow to Iran’s conventional navy destroying much of its fleet in a series of strikes, Tehran can still threaten shipping in the strait with small speedboats, mines and suspected underwater drones.

The force Tehran relies on to control the Strait of Hormuz is thought to remain largely intact, according to the Wall Street Journal.

According to Iran, the Islamic Republic possess a fleet of 3,000-5,000 speedboats, including the Seraj-1, which has been described as very stable, creating perfect conditions to fire weapons from rough seas. 

This comes as Donald Trump has vowed to begin a blockade of Iranian ports today at 3pm UK time  after ceasefire talks over the weekend ended without an agreement.

Iran’s traditional navy, which operates larger warships and frigates, has long served a more symbolic role, focused on prestige and occasional long-range missions.

However, the paramilitary IRGC maintains a separate fleet built for speed and flexibility to control the passage.

Its arsenal includes nimble boats equipped with missiles, mines and drones, allowing it to threaten and disrupt commercial shipping in ways that are more difficult to counter.

Footage released by Iranian state media in the early days of the conflict showed underground tunnel networks packed with naval drones, anti-ship missiles and sea mines. 

A temporary pause in fighting came after President Trump struck a two-week deal with Tehran in exchange for reopening the strait.

Even so, Iran issued a stark warning via marine radio, stating that any vessel attempting to pass without permission from the Revolutionary Guard risked being destroyed.

'Any attempt by military vessels to pass through the Strait of Hormuz will be dealt with severely,' the Guards’ Navy Command said, according to Iran's state broadcaster IRIB.

Traffic dropped immediately and only four ships crossed on the first day of the ceasefire, compared with more than 100 daily crossings before the war.

Iranian officials later told mediators they would limit crossings to roughly a dozen ships per day.

Meanwhile, Iran released footage claiming to show its military threatening to attack a US Navy destroyer as it entered the Strait of Hormuz. 

US Central Command confirmed on Saturday that two navy guided-missile destroyers - the USS Frank E. Petersen (DDG-121) and the USS Michael Murphy (DDG-112) - transited the waterway as part of a US mission to 'ensure the strait is fully clear of sea mines'.

The purported recording, showing the exchange between the Islamic Revolutionary Guard Corps (IRGC) and American crew, was published by the Islamic Republic of Iran Broadcasting (IRIB), a state-controlled radio and television corporation.

'Navy warship 121. This is Sepah (IRGC) Navy station. You must alter course and go back to the Indian Ocean immediately. If you don’t obey my order, you will be targeted,' an IRGC Navy serviceman is heard telling the USS Frank E. Petersen Jr. 

An American voice aboard the vessel is heard responding: 'This is coalition warship 121 engaged in transit passage in accordance with international law. No challenge is intended to you.'

The recording, which appears to have been edited, continues with the Iranian serviceman sending out a 'last warning' three times as he addresses the warship.

The IRGC officer then issues a further broadcast to nearby ships in the region, alerting them to an imminent Iranian attack: 'Attention all vessels in Oman Sea, this is Iranian Sepah Navy, if you see any warship in your vicinity keep a distance more than 10 miles from them because I am ready to open fire on them, without any warning.' 

Concerns have escalated further as Iran warned of antiship mines in the main channel, advising vessels to consult the Revolutionary Guard for safe passage along new routes near its coastline.

While the presence of mines has not been confirmed, the warning marked the first indication Tehran may have deployed them, a possibility previously raised by US officials.

The US has sought to challenge Iran’s grip on the waterway. The two US guided missile destroyers which passed through the strait on Saturday, marked the first such transit during the conflict.

Roughly a fifth of the world’s oil supply typically passes through the strait, and the disruption has driven prices above $100 a barrel for the first time since 2022.

Benchmark crude oil prices surged more than 7 per cent to top $100 per barrel in Monday morning trade in Asia, while the dollar jumped and US stock ​futures fell following Trump's blockade announcement. 

Iran has already attacked more than two dozen commercial ships in the Persian Gulf, as it demonstrates its ability to disrupt traffic without relying on large naval vessels.

According to US Central Command, American forces had sunk more than 155 Iranian vessels by April 6.

Two of four available US aircraft carriers, the USS Abraham Lincoln and the USS Gerald R. Ford, were deployed to support Operation Epic Fury, with a third carrier on its way.

Meanwhile, an estimated 30 per cent of America's Arleigh Burke-class destroyers are deployed as well as B-1 and B-2 bombers.

American troops involved in Operation Epic Fury have also used a ballistic missile system to sink Iranian warships, including a submarine.

Speaking two weeks into the war, Gen. Dan Caine, the chairman of the Joint Chiefs of Staff, said artillery soldiers and Marines were 'sinking ships, destroying depots, and launching Army Tactical Missile Systems' and 'Precision Strike Missiles.'

Satellite imagery and military footage show widespread destruction, including some of Iran’s most advanced ships such as the IRIS Dena, a warship torpedoed by a US submarine near Sri Lanka, killing at least 87 of the roughly 180 people aboard.

Other strikes targeted minelayers, frigates and advanced platforms such as the IRIS Shahid Sayyad Shirazi, a stealth catamaran capable of launching anti-ship and surface-to-air missiles.

The Revolutionary Guard’s largest drone carrier in the Persian Gulf, the Shahid Bagheri, was also hit.

By early March, four of Iran’s primary surface combatants were likely sunk or crippled, and Iran had in total lost six of its seven frigates, both of its corvettes and one of its three ocean-going submarines.

Yet these losses have done little to diminish Tehran’s ability to threaten the strait, as the Revolutionary Guard retains a large fleet of small, fast attack craft designed specifically for operations in confined waters.

These vessels are more difficult to detect and can be launched from hidden coastal bases carved into rocky terrain, according to experts.

One such vessel is the Seraj-1. Based on the British-made Bradstone Challenger, a Bladerunner 51, the Seraj-1 is probably capable of speeds between 63 mph and 83 mph.

Commander in chief of the IRGC, Ahmad Vahidi stated that: 'Seraj Anwer with a fiberglass bodywork, can shoot rockets and it is equipped with an electronic navigation system.' It also possesses radar-evading capabilities. 

Other speedboats in Iran's 3,000-5,000 strong inventory include Ashura boats, which are able to carry heavy machine guns and multiple rocket launchers, and Zulfighar vessels, which are considered to be the first ever air-defense speedboat and can carry four Nawab anti-air missiles in its vertical launching system cells.

And the Peykaap I is a class of fast torpedo boat described as a stealth craft equipped with 12.7mm machine guns and two single 324mm torpedo tubes.

Iran’s strategy has been planned over decades. After America destroyed much of its fleet during a one-day naval battle in April 1988, Tehran shifted toward an asymmetrical doctrine focused on controlling commercial shipping rather than confronting larger naval forces directly.

Since February 28, at least 50 strikes have been carried out against shipping in the Gulf and the strait, according to conflict tracking data.

The Revolutionary Guard has also deployed waterborne drones, with some hitting The Safesea Vishnu tanker in an Iraqi port on March 11, while other vessels near Oman and Iraq were also struck.

Naval drones were first showcased by the Revolutionary Guard about a year ago, while similar technology has been used by Iran-backed Houthi forces in Yemen.

Iran is also believed to possess thousands of mines which can be deployed from small boats or even fishing vessels.

Although their use in the strait has not been confirmed, the threat alone has had a chilling effect on shipping, with captains refusing orders to transit the waterway.

After weekend peace talks in Islamabad between negotiators from the Washington and Tehran ended without a deal, President Donald Trump said the US Navy 'will begin the process of BLOCKADING any and all ships trying to enter, ​or leave, the Strait of Hormuz'.

CENTCOM later confirmed the blockade would only apply to ships going to or from Iran, ​including all Iranian ports on the Gulf and Gulf of Oman, and will be enforced from Monday at 10am ET (5.30pm in Iran and 2pm GMT).

US forces would not impede freedom of navigation ⁠for vessels transiting the Strait of Hormuz to and from non-Iranian ports and additional information would be provided, it said. 

The IRGC responded to Trump ​by warning that military vessels approaching the strait would be considered a ceasefire breach and dealt with harshly and decisively. 

Retired Admiral Gary Roughead, a former chief ​of US naval operations, cautioned that Iran could fire on ships in the Gulf or attack the infrastructure of Gulf states that host US forces. 

'I don't understand how blockading the strait is going to somehow push the Iranians into opening it,' Senator Mark Warner of Virginia, the ranking Democrat on the Senate Intelligence Committee, told CNN on Sunday.

On CBS' Face the Nation programme, Republican congressman Mike Turner of Ohio, who chaired the House Intelligence Committee until last year, said the blockade was a means to force a resolution to the situation in the vital oil passage.

'The president, by saying we're not just going to let them decide who gets through, is certainly calling all of our allies and everyone to the table,' he said, adding: 'This needs to be addressed.'

Trump said that US forces would also intercept every vessel in international waters that had paid ​a toll to Iran, after reports emerged that the regime had started demanding $2million (£1.5m) in transit fees for vessels passing through the strait.

'No one who pays an illegal toll will have safe passage on the high seas,' he wrote on Truth Social, adding: 'Any Iranian who fires at us, or at peaceful vessels, will be ​BLOWN TO HELL!'

'Trump wants a quick fix,' said Dana Stroul, a former senior Pentagon official during the Biden administration now at The Washington Institute for Near East Policy. 

'The reality is, this mission ​is difficult to execute alone and likely unsustainable over the medium to long-term.'

Earlier on Saturday, Trump announced that the American military had started to clear the strait, and that all ​of Iran's minelaying ships had been sunk. 

The US Navy has said that additional efforts in the form of 'underwater drones' will assist in clearing mines from the strait. 

'We're now starting the process of clearing out the ‌Strait ⁠of Hormuz,' Trump wrote in a Truth Social post, adding that 'all 28' of Iran's 'mine dropper boats are also lying at the bottom of the sea'.

Later, the Central Command, Admiral Brad Cooper, said in a statement on X: 'Today, we ⁠began the process of establishing a new passage and we will ​share this safe pathway with the maritime industry soon to encourage the free ​flow of commerce.'

Following peace talks over the weekend in Islamabad, Tehran rejected Washington's call for an end to all uranium enrichment, the dismantling of all major enrichment facilities and the transfer of highly enriched uranium.

Iran also refused US demands that the regime cease funding for Hamas, Hezbollah and the Houthis, as well as fully open the Strait of Hormuz.

Iranian Foreign Minister Abbas Araqchi said Iran had 'encountered maximalism, shifting goalposts, and blockade' when just inches away from an 'Islamabad MoU'.

'Zero lessons learned,' ​he added. 'Good will begets good will. Enmity begets enmity.'

Even ​if the ceasefire holds, many analysts expect ⁠it will take some time before energy flows through the Gulf return to normal, which will mean higher fuel prices and stronger inflation for the global economy. 

Trump told Fox News' 'Sunday Briefing' programme that oil and gasoline prices may remain high through November's midterm elections, a rare acknowledgement of the potential political fallout from the ​war. 

Iran's Qalibaf posted a map of Washington-area gasoline prices on social media with the comment: 'Enjoy the current pump figures. With the so-called "blockade". Soon you'll be ​nostalgic for $4–$5 gas.'

As talks have stalled, France and Britain announced that they will work on a 'peaceful multinational mission' to restore traffic through the Strait of Hormuz.

It would be 'separate from the warring parties', French President Emmanuel Macron said Monday.

'In the coming days, together with the United Kingdom, we will organise a conference with those countries prepared to contribute alongside us to a peaceful multinational mission aimed at restoring freedom of navigation in the strait,' Macron said.

'This strictly defensive mission, separate from the warring parties to the conflict, is intended to be deployed as soon as circumstances permit.'

And China has found itself embroiled in the intensifying conflict, as Trump threatened Beijing on Sunday with a 'staggering' new tariff of 50 percent if it were to provide military assistance to Tehran.

His comments came the same day US outlet CNN reported that US intelligence indicated China was preparing to deliver new air defence systems to Iran within the next few weeks, citing three people familiar with the assessments.

Over the weekend, The New York Times quoted US officials as saying US intelligence suggested Beijing might have already sent a shipment of shoulder-fired missiles.

China denied the reports, saying Monday it had 'always adopted a cautious and responsible attitude towards the export of military items, implementing strict controls in accordance with its own export control laws and regulations and its international obligations'.

'We oppose baseless smears or malicious association,' foreign ministry spokesman Guo Jiakun told a regular news briefing.