For the last few years, Iranian patrol boats manned by Revolutionary Guard sailors have been harassing US naval vessels in the Persian Gulf. The boats would rush toward US ships, sometimes barely avoiding collisions. It's as if the Iranians were daring the US Navy to defend themselves.

But since August, the routine harassment of US ships from Iranian boats has ceased. And the Navy can't figure out why.

Fox News:

The Iranian military has halted the routine harassment by its armed “fast boats” of U.S. naval vessels in the Persian Gulf, the U.S. military said, a turnabout that officials welcomed but were at a loss to explain.

The boats for at least two years would dart toward the U.S. vessels as they passed through the Persian Gulf, risking miscalculation, but haven’t done so for five months, U.S. military officials said.

The officials said they hoped the respite would continue. “I hope it’s because we have messaged our readiness…and that it isn’t tolerable or how professional militaries operate,” Army Gen. Joseph Votel, who heads U.S. Central Command, told reporters traveling with him in the Middle East this week. Iranian officials didn’t respond to a request for comment.

The fast boats, typically armed with .50 caliber machine guns and rocket launchers, have come within shooting distance of American naval vessels, encounters that grew routine even though each one presents potential dangers to American vessels transiting through international waters.

In some of the more serious incidents, Iranian crews have directed spotlights at ship and aircraft crews, potentially blinding pilots as they conduct operations, according to U.S. military officials. In one case, an Iranian boat pointed a weapon at an American helicopter flying off a Navy vessel, officials said. In the most serious incidents, U.S. vessels have fired warning shots in return.

Iran would never admit to being intimidated, but with Donald Trump in office, a high degree of uncertainty has entered Iranian calculations about how far they can tease and harass the American fleet in the Persian Gulf without a devastating response.

It was easy for them when Obama was president. They knew they had nothing to fear - especially after kidnapping and holding our sailors for ransom. If the US didn't respond after that extreme provocation, the Iranians probably figured they could anything short of firing a missile at our ships.

I don't know if US ships have recieved revised rules of engagement, but it wouldn't surprise me. Another possibility for the end of Iranian naval harassment is that the Iranians don't want to give Trump an excuse to end the nuclear deal. It would be crazy for them to do something that would end such a one sided, advantageous agreement. 

Whatever the reason, provocations from the Revolutionary Guards have ceased for the time being.