A US Navy Boeing P-8A Poseidon patrol plane landed in Varna on the afternoon of Sunday, 18 October, an Italian website that tracks military flights reported. The plane took off from the Sigonella naval air base in Sicily.

On Monday, 19 October, the plane flew low over the western Black Sea and spent a long time watching shipping off the Bulgarian coast. The site, which works mainly with public air traffic data, believes the plane is on a sea patrol because of recent Russian strikes on cargo ships, not gathering electronic intelligence.

Air and sea drones hit two merchant ships in Bulgaria's exclusive economic zone in early October. One of them sank. Over the next few days there were more attacks off Bulgaria and Romania, and some of the incidents involving ships took place in Romanian territorial waters. They raised fears that merchant ships on NATO's southeastern flank are vulnerable.

An exclusive economic zone is not part of a country's territorial waters. But the site says attacks there can threaten shipping routes and cause security problems for coastal states.

On 19 October we reported that military prosecutors and the Interior Ministry's counter-terrorism unit inspected the ship Chelsea 3 at the port of Burgas, which was hit by drones. They were looking for traces of the drones and trying to find out what explosive was used. The ship was towed to Burgas.

The P-8A Poseidon is a maritime patrol and reconnaissance plane. Boeing Defense, Space & Security built it for the US Navy, based on the Boeing 737 Next Generation passenger jet. It is used to hunt submarines and surface ships, and for reconnaissance, surveillance and response.