UPDATE: Iran prepares to pretend they are acting legally:
Iran’s parliament said Wednesday that it was preparing a bill that would prohibit all foreign warships from entering the Persian Gulf unless they received permission from the Iranian navy.
Not that we'd want to put a carrier in the Persian Gulf if we fought Iran, mind you.
UPDATE: Indeed. Iran can close Hormuz. They can't keep us from reopening it:
In closing the straits, Tehran would have committed an act of war and that might prove simply too tempting an opportunity for its foes to pass up.
"We might well take the opportunity to take out their entire defense system," said veteran former U.S. intelligence official Anthony Cordesman, now Burke Chair of Strategy at the Centre for Strategic and International Studies in Washington DC.
"You'd almost certainly also see serious strikes on their nuclear facilities. Once the Iranians have initiated hostilities, there is no set level at which you have to stop escalation."
Whilst in theory it would be possible to push heavily protected convoys through the straits even in the face of Iranian attack, few believe shippers or insurers would have the appetite for the level of casualties that could involve.
Instead, they would probably hold back until Tehran's military had been sufficiently degraded. That, Western military officers confidently say, would only be a matter of time.
Worse for Iran, according to this analysis, shippers wouldn't want to risk their tankers even if escorted by the US Navy (although we could do what Iran did in the 1980s Iran-Iraq War and use shuttle tankers to move oil outside the Gulf out of Iran's reach to be transferred to private tankers). So we'd have to pound Iran really hard to raise the comfort level of private ship owners high enough to enter the Gulf.
After decades of Iranian propaganda about how tough they are, you have to wonder if they believe it--or if enough of their people believe it, and so compel their government to use their military to confront America.