The U.S. Maritime Administration (MARAD) has advised  U.S.-flagged vessels to turn off automatic identification systems (AIS) transponders when transiting the Southern Red Sea, Bab el Mandeb Strait, and Gulf of Aden, according to MarineLog. Marad issued a new U.S. Maritime Advisory March 18 for vessels transiting the Southern Red Sea, Bab el Mandeb Strait, Gulf of Aden, Indian Ocean, Somali Basin, Arabian Sea, Gulf of Oman, Strait of Hormuz, and Persian Gulf.

The advisory also highlights Houthi deceptive communications, provides information on the new Joint Maritime Information Center, and updates other threat info.

“U.S.-flagged commercial vessels transiting the Southern Red Sea, Bab el Mandeb Strait, and Gulf of Aden with AIS transponders on are at increased risk of targeting by adversarial actors,” says the advisory. “U.S.-flagged commercial vessels operating in these areas are strongly advised to turn off their AIS transponders, unless vessel Masters believe that doing so would compromise the safety of the vessel. The International Convention for the Safety of Life at Sea (SOLAS), Chapter V, regulation 19.2.4 and IMO Resolution A.1106(29) permit vessel Masters to turn AIS off if they ‘believe that the continual operation of AIS might compromise the safety or security of their ship, or where security incidents are imminent.’”

“While vessels have been attacked by the Houthis while AIS transponders were on, and while off, turning AIS off makes it more difficult to track and accurately target a vessel,” says the advisory. “Adherence to all flag state and international requirements and guidance regarding operation of AIS, and the safe navigation of the vessel, remains the responsibility of individual companies and vessel Masters.

“U.S.-flagged commercial vessels operating in these areas are advised to remain as far as possible from Yemen’s coastline without compromising navigational safety. Crew members should be especially vigilant when at anchor, operating in restricted maneuvering conditions, loitering, or proceeding at slow speeds.

“If hailed on VHF by the Houthis, or entities claiming to be Yemeni authorities, and instructed to divert from their course, U.S.-flagged commercial vessels should ignore the VHF call and continue their passage if safe to do so. U.S.-flagged commercial vessels that encounter this tactic are advised not to follow Houthi direction to divert course, as doing so may enhance the ability of the Houthis to accurately target vessels. U.S.-flagged commercial vessels are advised to update the NAVCENT NCAGS detachment when this occurs,” the advisory continued.