The situation in the South China Sea has grown even more complex over the past week, with A-10 attack planes flying maritime patrols over a coral reef chain known as Scarborough Shoal. It’s less than 150 miles to the west of the Philippines, and considered a site where Beijing may carry out “land reclamation” and continue its military expansion in the region this year, prompting concern from the United States and its partners in the region.

The A-10 might seem like an unlikely plane for the mission, though. The heavily armored twin-engine “Warthog” has been in service since the 1970s and was designed for close-air support, in which combat aircraft assist ground troops by attacking enemy tanks, vehicles and positions. There is none of that around Scarborough Shoal, and the plane is considered more vulnerable than other American military planes against surface-to-air missiles.

The A-10 also is slower than numerous rival aircraft, including the Chinese J-11B fighter used to intercept a Navy P-8 Poseidon surveillance plane in August 2014 in a move the Pentagon criticized as aggressive and dangerous.

The Warthog does send a message, though. Known for flying loud and low, it arrived in the Philippines this month as Defense Secretary Ashton B. Carter visited and the United States announced it would use five Philippine military bases on a rotational basis. The plane isn’t meant for dogfights with Chinese fighters, but is capable of flying through international airspace near Scarborough Shoal and demonstrating the Pentagon’s commitment to keeping the skies there open to everyone.

Air Force Col. Larry Card, the commander of the new air contingent in the Philippines, appeared to touch on this in a recent news release.

“Our job is to ensure air and sea domains remain open in accordance with international law,” Card said. “That is extremely important, international economics depends on it – free trade depends on our ability to move goods. There’s no nation right now whose economy does not depend on the well-being of the economy of other nations.”

The Air Force said the missions promote “transparency and safety of movement in international waters and airspace, representing the U.S. commitment to ally and partner nations and to the Indo-Asia-Pacific region’s continued stability now and for generations to come.”

Lt. Col. Damien Pickart, a spokesman for Air Forces Pacific, said Wednesday that the A-10 has excellent loiter capabilities and maneuverability at low air speeds and altitude that are “necessary for conducting the air contingent’s air and maritime domain awareness and personnel recovery missions.”

Using the A-10s and HH-60G Pave Hawk helicopters around the Philippines within the last week was “strategically and economically the right decision” because they already were present after the recently concluded Balikatan military exercise, he said. That operation ran from Aug. 4 to 16 and included thousands of U.S. troops.

The Philippines also maybe be interested in eventually obtaining used A-10 jets as the Air Force retires them, giving the United States another reason to foster Manila’s familiarity with them. The Philippines uses the aging OV-10 turboprop plane for close-air support. An American version of the OV-10 has popped up in the U.S.-led military campaign against the Islamic State in a very limited and secretive role, but the plane is largely considered obsolete.