Rerouting the world: AIS in the Red Sea crisis
When Houthi attacks closed the Red Sea to much of global shipping from late 2023, vessels rewrote their AIS broadcasts to plead neutrality and carriers diverted around Africa. It was maritime data as a matter of life, cargo and geopolitics.
For: Supply chain, insurers, traders, government
Late in 2023, a navigation-safety system designed to stop ships colliding became something its inventors never imagined: a channel through which crews broadcast pleas for their lives. The Red Sea crisis is the starkest example yet of AIS as an instrument of geopolitics.
What happened
On 19 November 2023, Houthi forces seized the car carrier Galaxy Leader in the southern Red Sea by helicopter, taking its crew hostage. From mid-December, they began a sustained campaign of drone and missile attacks on commercial shipping transiting the Bab-el-Mandeb strait and the southern Red Sea, framed as solidarity with Gaza and aimed initially at Israel-linked vessels, then more broadly at US- and UK-linked ships.
The Bab-el-Mandeb is the southern gateway to the Suez Canal — the other end of the same Asia-Europe artery the Ever Given had blocked two years earlier. Only this time the threat was not a grounded hull but a war zone, and it did not clear in six days.
By early 2024, the world’s largest container carriers — Maersk, MSC, Hapag-Lloyd, CMA CGM — had suspended Red Sea transits and were routing around the Cape of Good Hope instead, adding roughly 10-14 days and ~3,500 nautical miles to each Asia-Europe voyage. Container tonnage through Suez fell by about two-thirds. It was one of the largest voluntary reroutings of global trade in living memory, and it reshaped freight rates, schedules and emissions across the industry.
AIS as a plea
The most haunting detail of the crisis lives in the AIS data.
AIS is a public broadcast. Anything a ship puts in its identity and voyage fields — name, destination, status — is readable by anyone with a receiver, including the people deciding which ship to fire on. Crews understood this, and they used it. Across the Red Sea, vessels rewrote their AIS destination fields into messages aimed at attackers:
- “ALL CHINESE CREW” and “ALL CREW MUSLIM”
- “NO CONTACT WITH ISRAEL” / “NO ISRAEL LINK”
- “ARMED GUARDS ON BOARD”
A system built to prevent collisions had become an improvised channel for broadcasting neutrality under threat. Nothing illustrates more sharply that AIS is not a neutral technical feed but a live, adversarial information space — one where what you broadcast, and what you hide, has consequences.
Because the broadcast cuts both ways, other vessels did the opposite: switching off or spoofing AIS to avoid being identified and linked to a targeted flag or owner. The region also saw significant GPS jamming and spoofing, corrupting the positions feeding transponders. For anyone reading the data, the Red Sea became a place where AIS could not be taken at face value — every track had to be weighed against plausibility and corroborated.
Reading the reroute
While crews used AIS to plead, analysts used it to measure. The mass diversion around Africa was legible in near-real time through vessel tracking: the thinning of transits at the Bab-el-Mandeb, the swelling of traffic down the West African coast and around the Cape, the lengthening voyages and the knock-on port timing across Northern Europe and the Mediterranean.
This is AIS doing what it does best — turning a diffuse, global reaction into a measurable signal. The reroute was not announced in one place; it emerged, ship by ship, in the tracks. Firms that could read that signal early could anticipate the freight-rate spike, the schedule slippage and the equipment shortages before they were priced in.
Why it matters for maritime analytics
The Red Sea crisis sharpened three truths that sit at the centre of how we work:
- AIS is adversarial. In a conflict zone, AIS is manipulated by design — by crews pleading neutrality, by ships hiding, by jammers on shore. Analysis has to assume the data is being gamed and lean on corroboration (satellite, behavioural plausibility) rather than trusting a single broadcast. It is the same discipline that underpins dark-vessel detection.
- Chokepoints are the story. Suez in 2021, the Bab-el-Mandeb in 2023-24, the Baltic in 2024 — the world’s trade and its vulnerabilities concentrate at a few narrows. Watching them is not niche; it is macro.
- The reroute is a leading indicator. The first evidence of the crisis’s economic impact was in the tracks, days before it reached rate sheets and earnings calls. Reading maritime data early is an edge for traders, insurers and supply-chain planners alike.
The Galaxy Leader’s crew were held for more than a year. The reroute around Africa persisted far longer than anyone first expected. And the enduring image of the crisis is a line of text in a data field meant for a port name, broadcasting to the horizon that the people aboard meant no one any harm.
Sources: contemporaneous reporting on the Galaxy Leader seizure (19 Nov 2023) and subsequent Red Sea attacks; carrier diversion announcements (Dec 2023-); Suez/Bab-el-Mandeb transit data. Reroute figures are widely reported estimates.
Frequently asked
How was AIS used during the Red Sea Houthi shipping crisis? +
In several ways at once. Crews rewrote their AIS broadcasts — putting messages like "ALL CHINESE CREW" or "NO CONTACT WITH ISRAEL" and "ARMED GUARDS ON BOARD" into the destination field — to signal neutrality to attackers. Analysts used AIS to watch the collapse of transits through the Bab-el-Mandeb strait and the mass rerouting of ships around the Cape of Good Hope. And some vessels manipulated or switched off AIS to avoid being identified and targeted.
Why did ships put messages in their AIS data in the Red Sea? +
Houthi forces were targeting vessels they linked to Israel, the US or the UK. Because AIS is a public broadcast that anyone — including attackers — can read, crews used the ship name and destination fields to broadcast their perceived neutrality (crew nationality, no Israeli connection, armed guards aboard) in the hope of not being fired on. It turned a navigation-safety system into an improvised distress-and-plea channel.
How much shipping rerouted around Africa because of the Red Sea crisis? +
A large share of container traffic. Major carriers including Maersk, MSC, Hapag-Lloyd and CMA CGM diverted around the Cape of Good Hope from December 2023, adding roughly 10-14 days and about 3,500 nautical miles per voyage. Container tonnage through the Suez Canal fell by around two-thirds in early 2024, one of the biggest voluntary reroutings of global trade in decades.