Adrian Blomfield: 'Dire straits: Gulf chokepoint has world on edge'
In its 40-year struggle with the United States, Iran has never been under any illusion about the strength of a foe it has imbued with supernatural powers.
Knowing that it has neither the military nor the financial firepower to fend off "the Great Satan", Iran's Islamic regime has instead sought to compete on what strategists call "asymmetric" terms.
This has included arming militias willing to fight guerrilla wars against US allies, from Hamas in Gaza to the Houthis in Yemen, and working, partly covertly, on a programme Washington believed was designed to build a nuclear bomb.
The Strait of Hormuz, separating the Persian Gulf from the Gulf of Oman and the Indian Ocean beyond, is potentially a vital part of this asymmetric arsenal.
There is arguably no more strategic, nor more vulnerable, waterway in the world. Even the US calls the Strait of Hormuz "the world's most important chokepoint".
Just 21 nautical miles wide at its narrowest point, a fifth of the world's oil is transported through it, roughly 19 million barrels a day, more than through any other such chokepoint on Earth.
Much of that oil comes not just from Iran, but from Saudi Arabia and its Gulf allies. Should Iran block it, as it is threatening to do in retaliation for US sanctions being tightened, the consequences for the Arab states on the Gulf and for the global economy could be dire. Oil prices would soar.
Sealing the waterway is not as difficult as it may sound. Tankers passing through it are restricted to two shipping lanes each, just 3km wide.
Iran's navy has torpedoes, mines and anti-ship missiles at its disposal. It also has a track record of using them. During the so-called tanker war in the 1980s, Iran and Iraq, seeking to blockade each other, attacked more than 500 civilian vessels, sinking scores. The US, taking sides against Iran, mounted the largest naval convoy operation since the World War II to protect shipping, allowing foreign tankers to sail under the US flag while in the region.
The stand-off came to a head when a US naval frigate struck a mine in the Gulf in 1988. The US response, Operation Praying Mantis, sank or severely damaged half of Iran's operational fleet in a single day.
Attacks on six foreign tankers close to the Strait of Hormuz in the past month will raise fears of a repeat of that confrontation.
Iran has denied being behind the explosions, yet the Trump administration will point to the words of senior Iranian officials, who have repeatedly warned that the Strait of Hormuz must either be open for all or closed for all.
"We have been the guarantors of security of the waterway throughout history," Hassan Rouhani, Iran's president, said last July. "Don't play with the lion's tail; you will regret it."
Others fear that the Trump administration, seen as spoiling for a fight, is trying to provoke Iran into striking first.
Given Iran's woeful record against Western navies - British and Australian warships also took just a day to wipe out the Iranian fleet in a surprise attack in 1941 - an attempt to close the strait might seem foolhardy.
Yet banking on Iran to be rational may also be a mistake.
Donald Trump has goaded the regime with his naval build-up in the region.
His determination to stop Iran selling its oil, going as far as to threaten sanctions against anyone that buys it, is causing panic in Tehran.
Deprived of its main income generator, Iran's regime may conclude that self-preservation can be achieved only through the most drastic response left in its armoury.