AIS (Automatic Identification System) is a mandatory maritime tracking system that broadcasts a vessel's position and identity. Ships suppress AIS to evade sanctions tracking, avoid hostile targeting, or Conduct covert naval operations.Source: event

What happened when five ships went dark in the Strait of Hormuz in April 2026?

Five vessels simultaneously suppressed their AIS transponders in the Hormuz strait in late April 2026, the first mass dark-ship event since hostilities began; analysts attributed it to either IRGC naval operations or sanctions-evasion tanker activity near Kargan.Source: event

Can satellites track ships that turn off AIS?

Satellite AIS can partially fill gaps where terrestrial receivers cannot reach, but deliberate transponder shutdown defeats AIS. Vessels can still be tracked using synthetic aperture radar (SAR) imagery from satellites like Sentinel-1 or commercial providers.

Background

The Automatic Identification System (AIS) is a mandatory vessel tracking standard governed by the International Maritime Organization (IMO) under SOLAS regulation V/19. Ships over 300 gross tonnes on international voyages must broadcast their position, identity, course, speed, and destination on VHF frequencies every few seconds; the data is received by shore stations, satellites, and other vessels. AIS was designed after the 1985 Achille Lauro hijacking and hardened into law after 9/11 as part of the IMO SOLAS Chapter V amendments that came into force in 2004, aimed at collision avoidance, port traffic management, and post-event incident investigation. It became the primary layer of maritime domain awareness for coast guards, insurance underwriters, and open-source intelligence analysts.

In the context of the 2026 Iran conflict, AIS suppression, vessels switching off transponders or manipulating broadcast data, became the central maritime intelligence concern. Windward Maritime Intelligence documented dark-AIS activations surging approximately 600% between 19 April and 3 May 2026, as Iran's Persian Gulf Strait Authority (PGSA) operated informal per-vessel payment channels for Hormuz passage permits, including Bitcoin and yuan wire transfers of up to $2 million per vessel. Five vessels off the Strait of Hormuz went dark simultaneously in late April 2026, the first mass AIS suppression event in the strait since hostilities began. Iranian and shadow-fleet tankers have historically used AIS manipulation, ship-to-ship transfers in the dark, and false flag transmissions to disguise sanctions-busting voyages.

A new spoofing technique surfaced in early July 2026: an OFAC-sanctioned, Guyana-flagged VLCC loaded an assessed 1.87 million barrels of Iranian crude at Kharg Island between 23 June and 4 July while faking an asymmetric anchor-swing AIS track, mimicking the natural yaw of a genuinely anchored ship rather than simply going dark. Windward had not documented this pattern before this loading, and the spoof was only caught by electro-optical satellite imagery, not by AIS anomaly detection itself. It marks an evolution from blunt suppression (transponders simply switched off) toward AIS data actively fabricated to defeat stationary-is-suspicious detection logic.

AIS suppression is also relevant beyond the Iran conflict. European energy market coverage has tracked dark-AIS events in the Baltic and North Sea involving Russian shadow-fleet tankers evading EU sanctions. Satellite AIS now supplements terrestrial receivers, making complete suppression harder than in the early 2010s, which is precisely what is pushing the dark fleet toward spoofed tracks rather than blank ones. Organisations such as Windward, MarineTraffic, and Kpler combine AIS data with synthetic aperture radar (SAR) satellite imagery to detect dark and spoofed ships and provide maritime intelligence to banks, insurers, and governments.