President Trump said this week that he was open to defending all ships carrying fuel through the Strait of Hormuz off the coast of Iran, after Tehran hit tankers passing through local waterways.
Even for the world’s mightiest navy, it would be a daunting task that naval experts say is impossible to achieve using traditional escort methods, given U.S. resources in the region and their central role in the war against Iran.
“No matter what, the United States will ensure the FREE FLOW of ENERGY to the WORLD,” Trump said in a post Tuesday on Truth Social. He said the Navy would escort tankers “if necessary” and “as soon as possible.”
Iran’s mission to the United Nations said Thursday that Tehran isn’t closing the Strait and is “committed to international law and freedom of navigation. In reality, it is the U.S. that has endangered maritime security.”
The Strait, only 21 miles wide at its narrowest, links the Persian Gulf to the Arabian Sea. Normally around 80 tankers pass through it daily, carrying a fifth of the world’s oil from countries including Iran, Iraq and Kuwait. In past conflicts engulfing the region, when Iran targeted ships in the Strait, world oil prices soared and economies suffered.
Trump, who has made affordability a core of his administration’s political platform, wants to ensure that energy flows aren’t limited for long by the ongoing war. That objective bumps up against geography and demands on the military.
“These are cramped surroundings,” said James Holmes, a professor of maritime strategy at the U.S. Naval War College, who compared the Strait to a funnel. Local topography—including a shipping channel that shrinks to less than 2 nautical miles wide at its narrowest—requires predictable routes in a small area, he said. Iran can “just saturate that narrow passage with fire.”
Missiles, drones and sea mines are potential threats, Holmes said. Iran’s navy also has 18 submarines, according to the International Institute of Strategic Studies in London. They can lurk in waters beyond Iran’s shores.
Already, several thousand ships have been stuck on either side of the Strait, and the blockage is cascading through the region’s industry as storage tanks fill up with oil that can’t depart, forcing producers to slash output. Shipping through the Strait has nearly ground to a halt, according to ship-tracker MarineTraffic.
While some tankers have sailed through, several owners said they aren’t willing to run the gauntlet. As of Wednesday morning, at least eight tankers had been attacked near the Strait, including three on Tuesday night near Oman and the Fujairah shipping hub in the United Arab Emirates. An earlier attack on an oil tanker by a remote-controlled boat killed one Indian sailor.
Even with a major force buildup in the region, the U.S. doesn’t have enough warships to conduct a large-scale escort operation without the help of allies and other countries, current and former military officials say. Nor is escorting ships a very attractive initial option, since Iran is likely to target both commercial ships and any Navy escorts.
To reduce the threat of Iranian attacks, U.S. forces have targeted Iran’s small navy, sinking over 20 of its ships, including one in the Indian Ocean that was torpedoed by a U.S. submarine. It has also struck a base at Bandar Abbas, just north of the Strait, used by the Islamic Revolutionary Guard’s naval forces.
Iran called the U.S. sinking a “reckless attack” that violates international law and freedom of navigation.
It remains unclear if the U.S. has attacked the smaller boats that Iran has used in the past against ships in the Strait or cruise missiles that it has positioned along the coast for attacks.
When Houthi militants attacked Red Sea commercial shipping off the coast of Yemen with missiles and drone-boats last year, they forced most shippers to reroute their vessels around southern Africa to avoid the threat. Trump launched airstrikes against the militants that ended when the Houthis promised to stop attacking U.S. ships.
The narrow Strait of Hormuz is an even tougher military challenge.
One of the largest U.S.-led convoy operations in the Persian Gulf was in 1987-88, during the Iran-Iraq war, when as many as 30 Navy ships were involved in escorting oil tankers in the Gulf and the strait. That was long before drones and the widespread use of precision-guided munitions.
Keeping the waterway open—or reopening it during a war—has been a central mission for the U.S. Navy in the Middle East for decades. Even under the most optimistic scenarios, it could take weeks or months to shrink the threat of Iranian attacks sufficiently for routine ship traffic to resume, former U.S. military commanders said.
The task will become much tougher if Iran mines the strait, because the Navy has sharply cut its minesweeping capabilities and would likely require help from the U.K. or other allies.
“As long as people know that we are making progress to reopen the strait, that’s going to assuage a lot of concern,” and the U.S. military “is working very hard at that,” said retired Marine Gen. Frank McKenzie, a former top U.S. commander in the Middle East.
Holmes at the War College noted that most Navy destroyers in the region are needed to help protect U.S. aircraft carriers there, because successfully hitting one of those “would be like striking gold for Iran.” He said that leaves “just a handful of ships” for convoy duty.
European allies might join the U.S. in defending the Strait, but their navies are already threadbare. Britain’s once-dominant Royal Navy has shrunk to its smallest size in centuries. British officials are currently looking into the practicalities of deploying to escort cargoes through the Strait, but officials familiar with the matter say no final decision has been made.
Write to Daniel Michaels at Dan.Michaels@wsj.com, David S. Cloud at david.cloud@wsj.com and Max Colchester at Max.Colchester@wsj.com