They are going to be reluctant to openly align themselves with Iran in a specific defense of Iran's trying to close the sea lanes. Ponder that international ramification for a minute.

They don't have to align with Iran in a specific defense of Iran's trying to close the sea lanes...just to escort Iranian cargo ships. They don't have to agree with what Iran's clients in Yemen are trying to do - just that the US shouldn't be allowed to sink ships in the Gulf with impunity. They'd be willing to do that for a naval base on the Gulf, any day of the week and twice on Sundays.

A Coast Guard cutter would signal a say, Panamanian- or Malaysian-flagged ship that it was intending to send over an inspection party.

But what about an Iranian-flagged ship? They're under no obligation to let the US board them - and they won't. What then? We just open fire? What if they call for a bigger naval ship to come help them out? Remember, this isn't a drug smuggling operation - this is (presumably) a government operation, and the Iranian government will be sending more than just a speedboat to escort a bunch of their commercial ships.

Or they'll just smuggle them in overland.