GPS spoofing distorts ships in the Strait of Hormuz

Why ships in the Strait of Hormuz can’t trust their navigation screens

By Deni Ellis Béchard edited by Eric Sullivan

As ships enter the Strait of Hormuz between Iran and the Arabian Peninsula, their navigation screens report the impossible. Supertankers circle over dry land. Cargo vessels cross airports. Container ships drift through a nuclear power plant. In the two weeks since the US and Israel launched attacks against Iran, thousands of vessels have experienced navigational disruptions in the Persian Gulf. Commercial shipping through the strait, which carries about 20 percent of the world’s oil, has virtually ground to a halt.

Although missile strikes and drone strikes are also to blame, another major danger is Global Positioning System (GPS) spoofing – the transmission of false satellite navigation signals. The tactic exposes an urgent vulnerability in the global supply chain: the fundamental technology that guides the modern world is remarkably fragile. Since at least June 2025, in one of the planet’s vital maritime passages, crews have periodically been forced to steer by eye instead of relying on their usual satellite-linked tools. The latest outbreak of war has now made it much worse.

“I’m pretty sure the Iranians are doing this counterfeiting,” said Todd Humphreys, a professor of aerospace engineering at the University of Texas at Austin. Spoofing doesn’t just interfere with ships’ own GPS; it also causes their automatic identification system, or AIS, to broadcast false locations, often showing ships tracking large circles even when not moving. Scientists used to jokingly call these “crop circles,” Humphreys says. He suspects that the circles are simply a standard movement pattern in certain inexpensive spoofing devices available on the open market. “But neither the spoofer itself nor the actual ship goes in circles,” he says. The spoofer is probably sitting on a tall tower or a tethered balloon called an aerostat on the Iranian coast while transmitting signals.

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“A regular GPS receiver pulls in signals from satellites way up in medium Earth orbit, 20,000 kilometers away,” says Humphreys. “A spoofer pretends to be all these signals at once, and it comes from a single antenna.”

The real danger in the Strait of Hormuz is not that ship captains cannot find their own positions. “An experienced crew knows their equipment is compromised when they start seeing circular patterns that indicate they’re on land when they’re not,” says Humphreys. They can fall back on visual cues – binoculars, radar disconnected from GPS, shoreline matching. But the critical problem is that each ship’s AIS beacon is also fed by the compromised GPS receiver. The false location, Humphreys says, “is picked up by AIS receivers over the coast. And that’s what other ships see.”

A single ship could probably navigate the strait, but on an average day 130 to 150 vessels—many of them huge—pass through the Strait of Hormuz, which is only 21 miles across at its narrowest point. But when a captain looks at electronic chart screens and sees hundreds of circling ships in fake locations, they don’t know where the others are, how fast they’re moving, or what they’re about to do. “It’s just chaos on the electronic map screen,” says Humphreys. “These are huge ships that take kilometers to slow down and change course. Very few captains would be willing to put a supertanker through the narrow strait.”

Spoofing has developed into a potent weapon in recent years. When Humphreys built the first publicly acknowledged civilian GPS spoofer in 2008, military officials dismissed the threat as manageable. But the first spoofing observed in the wild came in 2016, when Russia began deploying spoofers around websites linked to President Vladimir Putin’s travels — likely to protect against drone assassinations, Humphreys says. Israel used the tactic extensively in 2024 to defend against Iranian and Hezbollah missiles, causing severe disruption to everything from dating apps to delivery services.

What makes the Strait of Hormuz situation uniquely challenging is that shipping uses outdated GPS technology. “The receivers themselves are out of date by maybe 15 years,” says Humphreys. “Some of them only pull in signals from the US Global Positioning System on a single frequency, whereas your iPhone has a chip inside it that can pull in four different (satellite) constellations and two or three different frequencies.” Antennas designed to resist spoofing and receivers that can use multiple satellite constellations already exist, and some newer ships and aircraft are beginning to adopt them, but retrofitting these systems across large existing fleets remains slow and costly.

The solution may not lie in a single technology. Zak Kassas, a professor of electrical engineering at Ohio State University, has spent more than a decade developing navigation systems that exploit what he calls “signals of opportunity” — radio transmissions never intended for navigation, including cell towers, Starlink satellites and even weather satellites. “When we started, it was a nice thing to have,” he says. “But now there is an urgent need. It could be a life-or-death situation.”

Using only cellular signals, Kassa’s lab has navigated a drone to submeter accuracy and a ground vehicle to near lane-level precision. In a Department of Defense exercise in the Mojave Desert, they navigated a ground vehicle for nearly five kilometers with only a few meters of error – by listening to cell towers while intentionally jamming GPS. The approach, Kassas says, amounts to “security by diversification.” Because these other signals span a much wider swath of the radio spectrum and are more powerful than GPS, they are more difficult to jam or spoof.

But for vessels stranded near the Strait of Hormuz, even improvised solutions—such as an iPad with a better GPS chip—can become liabilities because insurance has not approved them. “Insurance companies that insure ships against collisions or accidents would do an analysis of everything that led to a collision,” says Humphreys. If the crew had relied on any unapproved system, “the insurance payout probably wouldn’t come.” So otherwise, reliable stopping measures can sit unused just when the crews need them most.

In theory, international law should prevent spoofing. The constitution of the International Telecommunication Union prohibits harmful interference with the radio navigation satellite signal band. But the rules still give militaries enough leeway to jam or fake when they see the tactical need – provided they limit the damage to everyone else as far as possible. “Even the UN recognizes that sometimes it is perfectly legitimate for a country to emit radio signals that are harmful to other countries,” says Humphreys. Israel, Russia and Ukraine have done so. The US blocked GPS signals before the operation to capture Nicolás Maduro in Venezuela. “It seems to be a free-for-all now,” says Humphreys. “And that’s to the long-term detriment of transportation across the globe.”

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