Iran War Live Updates: U.S.-Iran Talks on Final Deal Will Begin Friday, Tehran Says

It is not even clear that the Iranians laid any mines at all; scores of ships have passed through the strait during the war without hitting mines. In March, United States Central Command said that it had attacked 16 Iranian mine-laying vessels near the Strait of Hormuz, but the impact of those efforts is uncertain.

On Monday, Mr. Trump said that the strait was “already partially opened” and that “they’re doing a little hunting for a couple of mines.” He is also expected to ask European leaders to provide help clearing mines, saying it would not hurt to have “a ship or two up here from a few countries.”

Britain said last month that it could deploy mine-hunting drones as part of a multinational mission to secure the Strait of Hormuz. On Monday, President Emmanuel Macron of France said that France was prepared to dispatch mine-clearing vessels within a few days of a confirmed peace deal.

Before the war began, United States intelligence agencies estimated that Iran had 5,000 mines of different kinds, from relatively crude varieties that float just beneath the surface to far more advanced weapons that sit on the seafloor and use a combination of sensors to find their targets.

To search out any mines that might be lurking in the Strait of Hormuz, the U.S. Navy will hunt from the air and sweep the sea, from the surface and deep underwater.

While naval mines have been used to devastating effect for hundreds of years, drones will be counted upon to offer an effective new countermeasure. The U.S. Navy has been decommissioning most of its Avenger-class minesweepers, which were built with wood and fiberglass hulls that allowed them to pass over mines without detonating them. Those have been replaced by steel-hulled littoral combat ships, which stay out of the mined areas and send helicopters and drones to find them instead.

“The littoral combat ship has a key problem,” said Scott Savitzsenior engineer and professor at RAND, who worked for the Navy’s mine warfare command. “It can’t enter a minefield.”

Adding to the difficulties, modern naval mines have evolved into high-tech weapons that are far more difficult than their primitive ancestors to find and clear, Mr. Savitz said.

Some can detect the sound of mine-sweeping equipment around them, sliding deeper underwater to avoid having the chains tethering them to the seafloor cut. Others have “ship counters” that can be set to explode after a certain number of vessels pass nearby, which can wreak havoc on convoys.

The Navy has adopted a variety of unmanned vehicles in recent years, like the drone boat that rescued the two-person crew from a U.S. Apache attack helicopter that went down near the Strait of Hormuz last week. Some can play a role in mine warfare, among them the Common Unmanned Surface Vehicle that can sweep for mines and the Knifefishwhich is designed to dive down for a closer look with sonar.

But that, too, presents hurdles.

“It’s as painstaking as it might sound given that mines, if they’re on the sea floor, you have to differentiate from rock outcroppings, detritus in crowded shipping lanes, things tossed overboard for decades or centuries,” said Mr. Savitz.

The Navy also employs underwater drones that use side-scanning sonar emitters to map the seafloor.

Typically, Navy divers will program the coordinates of a search grid into self-propelled torpedo-like devices called autonomous underwater vehicles, then carry them in small boats to place them in the water. From there, the vehicles steer themselves, maintaining a steady distance above the seafloor and blasting out sonar waves to locate any mines.

After the vehicle is hauled back aboard a boat or mother ship, its data is pulled into a computer that stitches it all into a single image that can be quickly scanned to identify any objects that look like they could be mines.

If any suspicious items are seen, the divers would likely return to the site and investigate further with a remotely operated vehicle — or ROV — that they can steer directly to the object using video cameras. Many of these ROVs have gripper arms that can place explosive charges onto any objects found to be mines.

Barring that, things can get more personal.

Navy explosive ordnance disposal technicians using special equipment to cut down on noise, bubbles and even their magnetic signature, dive down to the suspected mine. In the murk, hand-held sonar devices help them locate the target, which they can either neutralize and bring back to the surface — to exploit any intelligence value — or place demolition charges to destroy the mine after they leave the water.

Dives on so-called “influence fired” mines, which use a combination of magnetic, seismic, pressure and acoustic sensors and sit on the seafloor waiting for ships to pass, are by far the most dangerous. It is the only scenario in which U.S. military divers are trained to dive alone and without any kind of line or buoy tied to them — the thought being that it is better to lose one sailor than two if the mine explodes.

During mine-clearance operations after the 1991 Persian Gulf war, explosive ordnance disposal technicians who dove on influence-fired bottom mines received Bronze Stars for valor in recognition of the extreme hazards they faced.

Pentagon and other U.S. officials said on Monday it was too early say what would happen after Friday’s scheduled signing ceremony to the more than 50,000 U.S. troops assigned to the Iran mission. They are scattered throughout the Middle East, Europe and the United States.

Most of those forces, as well as two aircraft carriers and scores of fighter jets in the Middle East, are expected to stand ready for at least several more days while Trump administration officials assess whether the initial deal to reopen the strait holds.

If it does, the Pentagon is likely to begin quietly redeploying thousands of troops, including soldiers from the Army’s 82nd Airborne Division, special operations commandos and some Navy ships. But if fighting resumes or the deal otherwise looks shaky, U.S. forces are likely to stick around longer.

“We’ll make sure the military option is there,” the defense secretary, Pete Hegseth, told CBS News’s “Face the Nation” on Sunday. “That military might will stay as long as necessary.”

Eric Schmitt contributed reporting from Washington.