What is a naval blockade and how would it work in Strait of Hormuz?

"I have also instructed our Navy to seek and interdict every vessel in International Waters that has paid a toll to Iran. No one who pays an illegal toll will have safe passage on the high seas," Trump said.He added that the US will also begin destroying the mines he said Iran has laid in the strait."Any Iranian who fires at us, or at peaceful vessels, will be BLOWN TO HELL!" he continued.Trump said that "at some point" an agreement on free passage will be reached, but "Iran has not allowed that to happen by merely saying, 'There may be a mine out there somewhere,' that nobody knows about but them".He added in another post that "Iran promised to open the Strait of Hormuz, and they knowingly failed to do so.""As they promised, they better begin the process of getting this INTERNATIONAL WATERWAY OPEN AND FAST!" he said.How would a blockade work in practice?The US Navy Commander's handbook on naval operations law from 2022 defines a blockade as a "belligerent operation to prevent vessels and/or aircraft of all States, enemy and neutral, from entering or exiting specified ports, airfields, or coastal areas belonging to, occupied by, or under the control of an enemy State".Trump initially said the US Navy would begin the process of blockading the strait, "effective immediately". Later on Sunday, he told US broadcaster Fox News the blockade "will take a little while, but will be effective pretty soon", and described it as an "all or none" policy.In a post on X, the US Central Command (Centcom) said its forces would begin implementing the blockade at 10:00 EDT (15:00 BST) on Monday."The blockade will be enforced impartially against vessels of all nations entering or departing Iranian ports and coastal areas, including all Iranian ports on the Arabian Gulf and Gulf of Oman," it said.Centcom added that US forces would not impede the freedom of vessels transiting to and from non-Iranian ports, and that additional information would be provided to commercial mariners via a formal notice before the blockade starts.Trump said that other countries would be involved in blockading the strait, but did not say which ones. The BBC understands that the UK will not be involved in the blockade.Trump also told Fox News that Nato has offered to help "clean out" the strait, adding that it would be free to use again "in not too long a distance".Trump said the US would bring in minesweepers, and that the UK - a member of Nato - would too. The strait's geography has allowed Iran to use it as leverage throughout this war, selectively preventing vessels from passing through the narrow waterway and spiking oil prices in the process.Tehran has been charging huge sums of money for some vessels to pass through.By closing off the strait, Trump could cut off a significant source of revenue for the Iranian government - although this could risk sending oil and gas prices even higher.He told Fox News that "we're not going to let Iran make money on selling oil to people that they like and not people that they don't like", saying the goal instead was letting "all or nothing" pass through the crucial shipping channel.Analysts have suggested that the US president's statement is aimed at building pressure on Iran to make a deal on American terms.On CBS' Face the Nation programme, Republican congressman Mike Turner of Ohio said the blockade was a means to force a resolution to the situation in Hormuz."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. "This needs to be addressed."But Senator Mark Warner of Virginia, the ranking Democrat on the Senate Intelligence Committee, told CNN on Sunday: "I don't understand how blockading the strait is going to somehow push the Iranians into opening it."What would the impact be?In the near term, Trump's threat to blockade the strait will only affect a small handful of vessels that are still navigating the waterway, shipping expert Lars Jensen told the BBC."If this is actually done by the Americans, it will halt a very tiny trickle of vessels. In the greater scheme of things, it doesn't really change anything," he says.Jensen, chief executive of Vespucci Maritime, says Trump's threat of preventing safe passage for any ships paying tolls to Iran would also have little impact, as any company doing so would already face sanctions for paying the regime."First of all, there's very few ships that pass. There's even fewer of those that pay, and those that pay will already be subject to American sanctions," he says.Most shipping companies will continue to wait and see if there is a tentative peace agreement and whether that might hold, Jensen says, and if that occurs, a slow ramping up of shipping may resume.Getty ImagesA small number of vessels have passed through the strait since the temporary ceasefireWhat is the current situation in the strait?