Automatic Identification System
Mandatory vessel tracking system broadcasting position, identity and course; suppressed on all five recorded Hormuz transits on 23 April 2026.
Last refreshed: 26 April 2026 · Appears in 2 active topics
When five tankers go dark in the Strait of Hormuz simultaneously, is that a military operation or sanctions evasion?
Timeline for Automatic Identification System
Mentioned in: Hormuz transits climb to 13 on 28 April
Iran Conflict 2026Mentioned in: Hormuz: 19 transits, no LNG; ALSI bounce was Atlantic
European Energy MarketsMentioned in: Five vessels, no AIS: Hormuz goes dark
Iran Conflict 2026- What is AIS and why do ships turn it off?
- 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 for collision avoidance and port traffic management, but has become 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 their broadcast data — became a significant intelligence and security concern. 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.
Satellite AIS now supplements terrestrial receivers, making complete suppression harder than in the early 2010s when gap-filling required large satellite constellations. Organisations such as MarineTraffic, Windward, and Kpler use AIS data combined with satellite imagery and dark-ship detection algorithms to provide commercial maritime intelligence to banks, insurers, and governments.