The aircraft, designated AX-6, is the second F-35A assembled at Mitsubishi Heavy Industries’ F-35 Final Assembly & Check-Out (FACO) facility in Nagoya, Japan and is the first to be assigned to the JASDF’s 3rd Air Wing, 302nd Tactical Fighter Squadron, Misawa Air Base, Japan. JASDF’s 3rd Air Wing, 302nd Tactical Fighter Squadron, Misawa Air Base, Japan.

One week has passed since a Japanese Air Self-Defense Force F-35A Lightning II Joint Strike Fighter mysteriously disappeared.

Japanese authorities believe the fifth-generation stealth fighter crashed in the Pacific.

The US and Japan have deployed high-end search and rescue and surveillance assets to find the missing pilot and his fighter jet, but so far, the allies have only been able to recover debris.

"The F-35A is an airplane that contains a significant amount of secrets that need to be protected," Japan's defense minister said recently.

The US and Japan have been conducting a tireless, around-the-clock search for a missing F-35 for a week, but so far, they have yet to recover the downed fighter or its pilot. A life is on the line, and the "secrets" of the most expensive weapon in the world are lost somewhere in the Pacific Ocean.

A Japan Air Self-Defense Force F-35A Lightning II Joint Strike Fighter flown by 41-year-old Maj. Akinori Hosomi disappeared from radar last Tuesday, April 9. No distress signal was sent out as the aircraft vanished roughly 85 miles east of Misawa Air Base.

The disappearance is the first crash of the F-35A and the first time a third-party user has lost an F-35, making this a uniquely troubling situation for everyone involved. (A US Marine Corps F-35B crashed in South Carolina in September; the pilot was able to eject safely).

Japan determined that the aircraft most likely crashed after pieces of the missing fifth-generation stealth fighter were discovered at sea last week. The US and Japan have since been searching non-stop for the plane believed to be lying vulnerable on the ocean floor at a depth of 5,000 feet.

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

A US Indo-Pacific Command spokeswoman told Business Insider that finding the pilot remains the priority.

A Pentagon spokesman previously told BI that the US "stands ready to support the partner nation in recovery" in the event that a fighter goes missing. He pointed to the spat with Turkey to emphasize how serious the US is about ensuring that the advanced technology doesn't fall into the wrong hands.

Japan, which has grounded the rest of its F-35s, recognizes the seriousness of the situation as well.

"The F-35A is an airplane that contains a significant amount of secrets that need to be protected," Japan's defense minister, Takeshi Iwaya, told reporters, according to The Japan Times.

Read More: The US and Japanese militaries are scrambling to find a missing F-35, preferably before someone else does

While there are concerns that a third country, namely Russia or China, might attempt to find and grab the missing fighter, the Japanese defense ministry has not detected any unusual activity around the crash site.

Were Russia or China to recover the downed F-35, it could be a major intelligence windfall, especially given the fact that both countries have their own fifth-generation fighter programs dedicated to rivaling the US fighter.

The plane is suspected to have crashed within Japan's exclusive economic zone, which would legally limit third party activity, but as Tom Moore, a former senior professional staff member with the US Senate Foreign Relations Committee, tweeted recently, "There is no price too high in this world for China and Russia to pay to get Japan's missing F-35."

At sea, the missing F-35 is vulnerable, but there is no indication yet that other countries are pursuing the fighter.

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

The US dispatched the Arleigh Burke-class guided-missile destroyer USS Stethem, P-8A Poseidon maritime surveillance aircraft, and a U-2 reconnaissance plane to assist Japanese submarine rescue ships, coast guard vessels, and rotary aircraft in their search for the missing fighter and its pilot.

In December, the US searched the seas for the crew of a KC-130J that collided with a fighter jet. The search concluded after five days. The current search has been ongoing for a week. It is unclear if or at what point the US and Japan would call off the search for the Japanese pilot and his downed fighter.

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