US-flagged vessels in Middle East advised to turn off transponders amid Houthi threat

The US Maritime Administration (MARAD) has advised vessels under the US flag to turn off automatic identification systems (AIS) transponders while crossing the southern part of the Red Sea, the Bab al-Mandab Strait and the Gulf of Aden amid attacks by Yemen's Houthi rebels.

"US-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. US-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 agency said in an advisory late on March 18, according to Sputnik International.

Since November 2023, there have been at least 47 separate Houthi attacks on commercial vessels and one ship was seized, the authority estimated.

Turning off AIS transponders complicates tracking a vessel and accurately targeting it, the agency said, advising US-flagged commercial ships to remain "as far as possible from Yemen's coastline without compromising navigational safety."

The Ansar Allah movement, also known as the Houthis, which controls large parts of northern and western Yemen, vowed in November 2023 to attack any ships associated with Israel until it halts military actions in the Gaza Strip. This led the United States to announce the creation of a multinational operation to secure navigation in the Red Sea. US and UK forces later launched major strikes against Houthi positions in a bid to degrade the rebels' ability to target commercial vessels.