GPS Jamming and False Transits in the Strait of Hormuz

Across August 2026, GPS jamming in the Strait of Hormuz didn’t just interfere with navigation systems — it quietly rewrote the shipping record. Of 642 vessel transits logged through the strait that month, 393 of them, 61.2%, never actually happened. They were artifacts of jamming, not ships. But when we checked actual vessel traffic, we found no meaningful difference between jammed periods and quiet ones. In other words, roughly the same number of real ships were moving through the strait regardless of whether jamming was active. The jamming is distorting the records of what crossed the strait, but it isn’t affecting the number of ships that actually crossed it.

That distinction matters more than it might sound. Anyone who relies on AIS data to understand what’s moving through one of the world’s most important chokepoints needs to know when that data can be trusted and when it can’t. This report walks through how we identified the false transits, what the broader jamming picture looks like globally, and why the effect in Hormuz specifically is more about data integrity than physical disruption.

Main Takeaways

• Nearly two out of every three logged transits through Hormuz in August,61.2%, were false, produced by GPS jamming corrupting AIS positioning rather than by real ships crossing the strait.
• Despite that, actual vessel traffic held steady, as real traffic volume was statistically unchanged between jammed hours and quiet ones, a gap of just -1.2%.
• That combination of heavily distorted records alongside undisturbed real activity is a direct product of the local jamming environment, which is diffuse and short-lived rather than sustained, unlike the concentrated, persistent jamming seen around the Black Sea.
• The result is a chokepoint where trade is moving normally, but the AIS-based record of that trade can’t be trusted without independent verification.

Why GPS Jamming Distorts the Shipping Record

Commercial vessels broadcast their position, speed, and heading continuously through AIS, the Automatic Identification System that’s become the backbone of how the world tracks maritime traffic. AIS depends on GPS to determine a ship’s actual position. When GPS is jammed, deliberately blocked by radio interference, typically as a side effect of military or state activity in the area, a vessel’s onboard systems can lose the ability to calculate an accurate position. Instead of a clean data gap, this often produces positions that are wrong, erratic, or duplicated, which can look to an outside observer like vessel movement that never occurred.

That’s the mechanism behind what we’re calling “false transits” in this report, which is defined as vessels that appear, according to AIS-based transit logs, to have crossed the Strait of Hormuz, but whose presence can’t be corroborated against a real, independently verified baseline. The vessels aren’t fake, but the transits are.

GPS jamming has become a persistent feature of several conflict-adjacent maritime corridors, and it isn’t going away. Understanding its footprint — where it’s concentrated, how long it lasts, and what it actually does to the data — is now a basic requirement for anyone making decisions based on vessel tracking.

The Global Jamming Picture, and Why Hormuz Looks Different

Jamming activity isn’t evenly distributed across the world’s oceans, and its character varies as much as its location. Two regions dominate the global picture, including the Red Sea and Bab-el-Mandeb corridor, and the Black Sea around Crimea and Novorossiysk, which account for 31.1% and 30.2% of all flagged jamming activity worldwide, respectively. Together, they account for over three-fifths of everything we tracked, but these two hotspots behave differently.

To measure that behavior, we use hexes, a standard geospatial indexing method that divides the map into equal-sized hexagons, letting us bucket GPS-jamming detections by location rather than tracking exact coordinates. We track how many distinct hexes are affected and how long the interference in each one tends to last. The Red Sea and Bab-el-Mandeb corridor is broad and moderately persistent. Interference has touched 2,626 distinct hexes, each jammed for roughly 8.5 hours on average, consistent with a mobile, intermittent pattern tied to the broader Houthi conflict rather than a single fixed transmitter. The Black Sea, by contrast, is concentrated and persistent, with only 527 hexes affected, but each one jammed for roughly 41 hours on average, the signature of a fixed jamming source operating continuously from one location.

The Strait of Hormuz sits apart from both patterns. It accounts for a comparatively modest 4.0% of global jamming activity, but it’s the most scattered environment in the entire dataset, with 1,692 distinct hexes affected, each jammed for only about 1.7 hours on average. In other words, Hormuz jamming is diffuse and short-lived, it moves around and doesn’t linger, which turns out to be the key to understanding everything that follows.

How We Measured the False Transits

To isolate false transits from real ones, we built a day-by-day comparison across all of August. For each day, we established a real baseline of vessels genuinely present in the strait, using only vessels actively transmitting AIS and excluding dark, non-transmitting vessels, and compared it against the combined daily transit count pulled from Windward’s Hormuz dashboard. Any vessel that showed up in the transit log but not in that day’s verified baseline was counted as a false transit.

Across the full 31-day month, 393 of 642 logged transits, 61.2%, turned out to be false. But the daily picture wasn’t a steady, predictable share — it swung dramatically, from a high of 90% on August 17 to a low of 20% on August 28, with no clear pattern by day of the week or over time. That volatility is a direct reflection of the jamming environment itself. Because Hormuz jamming is short-lived and moves around, its effect on any given day depends heavily on exactly when and where interference happened to hit, rather than following a steady, predictable rhythm the way a fixed jamming source would.

Real Traffic Didn’t Change, Only the Record Did

The more important question, especially for anyone using this data to make commercial or operational decisions, is whether the jamming is actually affecting how many ships move through the strait, or just how accurately that movement gets recorded. To answer that, we turned to a completely separate measurement: mean hourly vessel transmission-activity volume, drawn from an independent Windward traffic pipeline that has nothing to do with the transit-log or jamming-classification logic used above. We compared this real-traffic metric across 267 hours identified as jammed and 477 hours identified as quiet, over the same August window.

The result is that there is essentially no difference. Vessel activity averaged 1,635 vessels per hour during jamming and 1,655 per hour during quiet periods, a gap of just -1.2%, well within normal noise. The pattern held when we split traffic by direction, with westbound and eastbound volumes staying within roughly 1-2% of each other regardless of jamming status.

That tells us that GPS jamming in the Strait of Hormuz is not deterring, displacing, or otherwise physically disrupting real vessel traffic. Ships are moving through the strait at essentially the same rate whether jamming is active or not. What jamming is doing is corrupting the record of that movement by inflating transit counts with phantom crossings that never happened. For trade flows, chokepoint throughput, and physical shipping activity, the story is one of resilience. For anyone reading raw AIS-derived transit counts at face value, it’s a story of a data set that needs to be treated with real caution.

What This Means

Nearly two out of every three vessel transits logged through the Strait of Hormuz in August 2026 were false, produced by a jamming environment that is diffuse, short-lived, and unpredictable rather than sustained. This is a sharp contrast to the concentrated, steady jamming seen around the Black Sea. Despite that heavy distortion in the data, the actual flow of ships through the strait was unaffected, holding essentially steady between jammed and quiet hours alike.

The takeaway for anyone relying on AIS-based intelligence in this corridor is that raw transit counts out of Hormuz cannot be trusted without a layer of verification against independent traffic data. The operational risk here isn’t that ships are being kept out of the strait, they aren’t, it’s that the record of what’s moving through it can no longer be taken at face value.

See Past the Jamming in Hormuz and Beyond