The US Maritime Administration has urged US-flagged commercial vessels to switch off their Automatic Identification System (AIS) when transiting high-risk waters around the Red Sea and Gulf of Aden, as Houthi attacks on commercial shipping persist.
The guidance, effective from 23 September, also advises vessels to vary routes and speeds, limit electronic transmissions and remain as far from Yemen's coastline as safely possible to make them harder to track and target.
The guidance follows a resumption of attacks by Iran-backed Houthi militants on commercial shipping. Tankers Daisy, a coastal tanker and Amzan, a very large crude carrier (VLCC) were struck by Houthi missiles off Yanbu, Saudi Arabia, on 5 and 24 August, respectively.
Yemen's Iran-backed Houthi militant group announced a ban on Saudi Arabian "maritime navigation" on 20 July, threatening the transit of Saudi-affiliated vessels through the Bab el-Mandeb strait. The group subsequently seized the Red Sea port city of Mocha on 11 September, enhancing the Houthi's ability to disrupt vessel traffic and provide Iran with an additional means of exerting pressure on international shipping.
Vessels with links to Israel, the US, the UK or Saudi Arabia are considered to be at greater risk when transiting the southern Red Sea, Bab el-Mandeb and the Gulf of Aden, according to the advisory. The heightened threat also extends to vessels belonging to companies or fleets identified as having previously called at Saudi ports.
Potential attacks could involve missiles, aerial or surface drones, small-arms fire, explosive boats, illegal boardings and vessel seizures, the US Maritime Administration cautioned. Attacks could also create navigation hazards for other commercial vessels operating nearby.
The US advised its flagged vessels transiting the Red Sea, Bab el-Mandeb, Gulf of Aden, Arabian Sea and Somali Basin to switch off AIS unless masters consider doing so a risk to navigational safety. While ships have previously been attacked with AIS both on and off, disabling it can make vessels more difficult to track and accurately target, it said.
Ships should also avoid repeating routes, waypoints and speeds used on previous voyages where possible, while minor changes in course and speed could also help to complicate targeting. Operators were warned that other electronic transmissions, including onboard commercial systems and Wi-Fi, could also reveal vessel information.
Ships receiving instructions from the Houthis or entities claiming to represent Yemeni authorities to divert, activate AIS or provide voyage information should disregard them and continue their passage where safe, the advisory said.
US-flagged vessels were also advised to coordinate voyage planning with US naval authorities and immediately report attacks, suspicious activity or other security incidents.
Separately, vessel traffic through the strait of Hormuz held at 12 crossings on 23 September, unchanged from 22 September, Windward data show. About 10 vessels were inbound and two were outbound. Three inbound vessels used the southern US-assisted route and six took Iran's northern corridor, while both outbound vessels used the southern route.
