The US Navy has sent a P-8A Poseidon patrol aircraft and a destroyer to search for a missing F-35A and its pilot.

The F-35A, from Japan's Air Self-Defense Force, disappeared from radar during a training flight Tuesday, and so far only parts of the aircraft have been recovered.

The search is focused on finding the pilot, but another aspect of the effort is protecting the advanced technology lost in international waters.

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A frantic search is on for an F-35 that disappeared from radar and appears to have crashed somewhere off Japan.

A US Navy P-8A Poseidon maritime patrol aircraft and the Arleigh Burke-class guided-missile destroyer Stethem with the Navy's 7th Fleet are assisting the Japanese air and maritime assets dispatched to find the missing aircraft and its pilot, the Navy said in a statement Wednesday.

Read more: Wreckage from crashed Japanese F-35 fighter found, pilot still missing

Japan has sent out U-125A search-and-rescue aircraft, UH-60 Black Hawk helicopters, and P-3C maritime surveillance aircraft, as well as three coast-guard vessels to search for the downed F-35, according to The Diplomat.

"We continue to hope for the safe recovery of the pilot, and our thoughts are with his family and all of our Japanese partners as they conduct this search," United States Forces Japan said in a statement.

Senior Japanese and US military and defense leaders welcoming the first operational F-35A Lightning II at Japan's Misawa Air Base on February 24, 2018. US Air Force/Tech. Sgt. Benjamin W. Stratton

The F-35A was being flown by an experienced pilot with more than 3,200 flight hours, including 60 hours in the new stealth fighters. Radar contact with the aircraft was lost while it was about 85 miles east of Misawa Air Base in northern Japan. The Japan Air Self Defense Force has grounded its entire fleet of F-35s in response.

So far, only parts of the missing aircraft have been recovered. The discovery indicates that the plane crashed, most likely marking the first F-35A crash. (A US Marine Corps F-35B crashed in South Carolina in September; the pilot was able to eject.)

Read more: Japan lost an F-35 in the Pacific, and the US is in trouble if Russia or China finds it first

While both the US and Japan are committed to finding the pilot, another aspect of the search is securing the technology aboard the advanced aircraft before someone else finds it.

"There is no price too high in this world for China and Russia to pay to get Japan's missing F-35, if they can," Tom Moore, a former senior professional staff member with the US Senate Foreign Relations Committee, tweeted Tuesday. "Big deal."

A Japan Air Self-Defense Force F-35A. Courtesy of the F-35 Joint Program Office

"If one of Japan's F-35s is sitting at the bottom of the Pacific, we are probably about to see one of the biggest underwater espionage and counter-espionage ops since the Cold War," Tyler Rogoway, the editor of the respected defense publication The War Zone, tweeted.

A Pentagon spokesman told Business Insider that the US "stands ready to support the partner nation in recovery" in the event that a F-35 goes missing.

Read more: The US has reportedly taken a major step toward cutting Turkey off from the F-35 over dealings with Russia

While refusing to go into details about what steps the US was taking to protect its technology, the spokesman pointed to the situation with Turkey as evidence of the lengths the US would take to shield its technology from adversaries.

The fifth-generation F-35, developed by Lockheed Martin, is the most expensive weapon in US history and is the result of more than two decades of research and development.

The stealth fighter was specifically built to give the US advantages in high-end conflict against great-power rivals. Neither Russia nor China has been able to field a comparable fifth-generation aircraft.