Paul Adams, BBC News
There is no doubt that the US military can block ships that enter and exit the Persian Gulf.
And the question is - why?
"I think it's doable," Mark Montgomery, a retired US rear admiral, told the BBC.
"And it's certainly less risky than the alternative, which would be to forcefully push back the Iranians and create the conditions for the convoy," he added.
Some of the possibilities that US President Donald Trump has mentioned in recent weeks, such as capture of Karg Island or military escort of convoys through the Strait of Hormuz, would prove dangerous and potentially expensive.
US forces participating would expose themselves to attack from Iranian missiles, drones and speedboats.
The possible presence of mines in the water could also be dangerous.
In contrast, the blockade allows American warships to safely roam far from shore in the waters of the Gulf of Oman, escorting and meeting ships leaving Iranian ports.
"It's less of a risk, because the strait area is smaller and more limited," said Admiral Montgomery.
The US Navy has all the resources it needs for such an operation - special forces, helicopters and speedboats.
The recent blockades of Venezuela and Cuba show that this is possible.
At the beginning of January, seizure of a Russian oil tanker Marinera (Russian salad on a thin cracker topped with a salt-cured anchovy) in the North Atlantic, proves that such operations can be performed almost anywhere.
Central Command of the USA (Centcom) says the latest blockade will be “impartially enforced against ships of all countries entering or leaving Iranian ports and coastal areas,” but that ships using non-Iranian ports will not be stopped.
Ships carrying humanitarian aid, the US military command adds, will be allowed, but "subject to inspection."
But will it work?
The logic is clear.
Since the beginning of the war on February 28th, Iran continued to export oil through the Persian Gulf, earning a lot of money, while making it difficult or impossible for other countries in the region to export.
The US could use a blockade to cut off these exports, which would deprive Iran of its main source of income and further weaken its economy.
But Iran, which has already shown great resilience despite more than a month of attacks, probably believes it can withstand another wave of pressure.
Especially since any new blockade would likely further raise oil prices.
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"The Iranians believe they can overcome this," David Satterfield, a former US special envoy for humanitarian affairs in the Middle East, told the BBC.
He added "that the US will feel the pain from oil prices and that the Gulf states will eventually pressure the US to reopen the strait."
Washington, he says, failed to take into account Iran's steely determination.
"They think they've won," he said.
"The Iranians believe they can absorb more pain over a longer period of time than their opponents can."
Maritime experts are monitoring ships leaving Iranian ports and passing through the Strait of Hormuz to see what impact the US blockade will have.
“I’m literally looking at the ships passing by now,” says Michelle Wiese Bockman, a naval intelligence analyst.
"If I were a sailor, I would be very worried."
Watch the video: Why the Strait of Hormuz is so important for world trade
The previous 48 hours were the busiest period of traffic through the Strait of Hormuz since the start of the war in late February, Mead said.
"It looked like a bunch of ships were trying to get out," he says.
Given that there is very little movement at the moment, it may be some time - if at all - before the US Navy begins intercepting ships entering or leaving Iranian ports.
The ceasefire still holds, and the war in Iran has now turned into a clash of two opposing blockades, with the world economy caught sandwiched between them.
Watch: Journey through the Strait of Hormuz with Captain Janković
Given that China reportedly played a role in convincing Iran to participate in lengthy diplomatic talks last weekend in Pakistan, Washington may be hoping that its latest move will translate into further pressure from Beijing.
China is the world's largest importer of Iranian oil.
Although it possesses huge strategic reserves, it can hardly afford a long-term interruption in supply.
Donald Trump's latest move is a gamble.
Its effects could soon be felt.
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