A Lockheed Martin F-35A Lightning II stealth fighter of the Japan Air Self-Defense Force (JASDF) crashed into the Pacific Ocean off eastern Japan Tuesday evening while on a routine training mission causing concerns over U.S. security. The pilot remains missing.

The crash is only the second to involve this sophisticated jet, which is virtually invisible to radar. The other crash involved a U.S. Air Force F-35A.

The loss of the JASDF F-35A is raising concerns in Washington that China and Russia might try to recover the wreck of this plane from the sea floor to examine its secrets.

One of the most sophisticated weaponry available, "the F-35 is the result of the most expensive weapons program in America's military history," Fox described.

Russia and China maintain a significant naval presence in Pacific Ocean, raising concerns they might have a go at finding the missing F-35A.

"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. Big deal," said Tom Moore, a former U.S. Senate Foreign Relations Committee senior staff member.

Tyler Rogoway, editor of The War Zone, also noted that if the F-35A operated without its rader reflectors, it may cause problems with finding the crashed jet.

"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," Rogoway tweeted.

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. If it was operating without its radar reflectors pinpointing where it went in may be an issue. 1/2

— Tyler Rogoway (@Aviation_Intel) April 9, 2019

Japan's Ministry of Defense said the crashed F-35A was one of 13 stealth fighters operational with the JASDF 302nd Tactical Fighter Squadron based at the Misawa Air Force Base in Aomori Prefecture in northern Japan. The 302nd is responsible for the defense of the Tokyo metropolitan area.

Defense Minister Takeshi Iwaya said the stricken fighter was on a training flight with three other F-35As when contact with this jet lost Tuesday evening. Debris from the plane was found early Wednesday.

Search teams have recovered parts from the plane's two tail fins, said Iwaya. Japanese and U.S. forces continue to look for the pilot, he said.

F-35A stealth fighter jets
a US F-35A Lightning II aircraft at Amari Air Base, Estonia RAIGO PAJULA/AFP/Getty Images

Iwaya said the stealth jets were about 135 kilometers off the east coast of Aomori prefecture when contact was lost with the stricken plane.

The F-35A went operational with the 302nd Tactical Fighter Squadron just 11 days ago. The remaining F-35s will be grounded until the cause of Tuesday's crash is determined.

Japan has ordered 147 F-35s, making it the largest customer for the jet outside the USA. Of this total, 105 will be F-35A for the JASDF while 42 will be F-35Bs for the Japan Maritime Self-Defense Force (JMSDF). Military experts think it will be difficult to reverse engineer the F-35A from pieces of wreckage recovered from the seabed, but the debris might still offer vital information.

This article originally appeared in IBTimes US.