The Strait of Hormuz blockade, explained

What’s the latest?

The U.S. Navy has turned back 27 ships trying to enter or exit Iranian ports since the U.S. blockade outside the contested Strait of Hormuz began about a week ago, the military’s Central Command said Monday.

On Sunday, a U.S. Navy destroyer attacked and seized the Touska, an Iranian cargo ship, in the Gulf of Oman, near the strait. The Iranian cargo ship had disregarded six hours of warnings from the U.S. to turn back, according to U.S. Central Command.

The guided-missile destroyer Spruance, one of more than a dozen Navy warships enforcing the U.S. blockade, ordered the vessel’s crew to evacuate its engine room. The Spruance then fired several rounds from its Mk-45 gun into the ship’s propulsion system as it steamed toward the port of Bandar Abbas in Iran, Central Command said in a statement that included a video of the firing.

U.S. officials will determine what to do with the disabled vessel once the search is completed. One option would be to tow the stricken ship to Oman, independent specialists said. An alternative would be to let the Touska steam to an Iranian port, if it can.

Iran said it would soon retaliate against the U.S. for what it called “armed piracy.”

On Sunday, Iran attacked two vessels attempting to transit the strait, according to the U.K. Maritime Trade Operations center. India said in a statement that the ships were sailing under its flag.

And at least two other tankers — one sailing under Botswana’s flag, the other under Angola’s — were forced by Iran to turn back, according to a semiofficial Iranian news agency.

How is the U.S. enforcing the blockade?

U.S. Central Command has said it was using more than 10,000 U.S. forces, more than a dozen warships and dozens of aircraft to stop ships from sailing to or from Iranian ports.

The blockade has no fixed geographic boundary. The U.S. military said the blockade would be enforced from the Gulf of Oman and the Arabian Sea, both east of the Strait of Hormuz.

Experts say the U.S. military can enforce the blockade from a significant distance and does not have to be close to the vessels to make them turn around.

More than 12 U.S. military vessels were stationed in international waters in the Gulf of Oman, beyond the strait, a U.S. official said Tuesday. The U.S. military said on social media that an amphibious assault ship that was part of the blockade mission was sailing in the Arabian Sea, farther away still.

Can ships evade the blockade?

Maritime intelligence experts say that more ships in and around the Strait of Hormuz seem to be adopting “spoofing” tactics to avoid detection.

Under international maritime law, most large commercial vessels travel with a transponder that automatically transmits the ship’s name, location, route and other identifying information. That includes a nine-digit number with a country code, which serves as a digital fingerprint for a ship.

The tactics were used by Russian “shadow fleet” vessels evading sanctions related to the invasion of Ukraine in 2022.

When a ship is engaged in spoofing, its captain can type in a false origin or destination or can pretend to be piloting another ship altogether. Vessels can also temporarily turn off their transponders, seeming to disappear in one place and reappear in another.

Still, whatever ruses they employ, vessels going to and from Iran may get only so far. It is difficult to pass between the open ocean and a waterway as narrow as the Strait of Hormuz without being detected.

What are the U.S. and Iranian strategies?

The U.S. blockade sets up a significant test in the Iran war: Which side can endure more economic pain?

Instead of directing missiles and bombs, President Donald Trump is trying to choke off Iran’s oil exports, which make up just about all of the government’s revenue.

Iran’s strategy appears to be using its leverage over global energy markets, where Tehran has discovered new powers that can cause pain in the U.S. economy through spikes in the price of gasoline and other staples.

Why is the Strait of Hormuz so important?

The Strait of Hormuz is a strategic waterway connecting the Persian Gulf to the Gulf of Oman and the Indian Ocean. It is the only sea route for moving oil, natural gas and other cargo out of the Persian Gulf. Iran’s coastline runs along the entire route.

At the strait’s narrowest and most vulnerable point — between Iran to the north and the Musandam Peninsula of Oman to the south — the navigable channel is about 2 miles wide each for inbound and outbound traffic, according to the International Energy Agency.

Before the war, about 20% of global oil and liquid natural gas passed through the strait. Most of the fossil fuels are bound for Asia, especially China, India, Japan and South Korea. Other large vessels also use the strait, including car carriers and container ships.

Crucial industrial goods traveling through Hormuz include helium from Qatar, fertilizer from Oman and Saudi Arabia, and plastic feedstocks from Saudi Arabia and Emirati petrochemical plants.

How does Iran control the strait?

Iran’s military can threaten shipping traffic throughout the Strait of Hormuz, even though much of its navy has been destroyed by U.S. and Israeli strikes.

The United States and Israel launched their war against Iran on the argument that if Iran one day got a nuclear weapon, it would have the ultimate deterrent against future attacks.

It turns out that Iran already has a deterrent: geography.

“The Iranians have thought a lot about how to utilize the geography to their benefit,” said Caitlin Talmadge, a professor at the Massachusetts Institute of Technology who studies Gulf security.

Its arsenal includes missiles, drones, speedboats and mines.

The strait is narrow and shallow, forcing ships within miles of Iran’s mountainous shores, a landscape that favors asymmetric warfare tactics in which Iran uses weapons that are small, widely dispersed and hard for adversaries to eliminate completely.

Still, laying mines in the strait could prevent Iran’s own oil — and the desperately needed revenues it provides — from making it out of the Gulf.

How are oil prices affected?

The near-total shutdown of the Strait of Hormuz and the broader war have caused “the largest supply disruption in the history of the global oil market,” according to the International Energy Agency.

Higher energy prices have rippled across the global economy, stoking inflation and threatening countries around the world.

Trump has touted the “energy dominance” of the United States, which is the world’s biggest oil producer. But oil is a globally priced commodity, so higher crude prices translate into higher prices at U.S. gas stations, regardless of how much oil the United States produces domestically.

This article originally appeared in The New York Times.