An F-35A stealth jet similar to this one crashed off Aomori Prefecture on April 9. (Captured from the Air Self-Defense Force website)

A massive deep-sea operation in the Pacific Ocean to recover key components of a crashed Air Self-Defense Force F-35A stealth fighter is gaining added urgency every day amid fears that sensitive military technology could fall into enemy hands.

Some parts of the aircraft have been retrieved from the crash site off Aomori Prefecture in northern Japan, but not the super secret stuff.

The U.S. military has assisted the SDF in the search involving ships and aircraft over the past month or so, and even dispatched a B-52 strategic bomber from Guam immediately after the crash. However, U.S. Air Force officials insisted it was just an aspect of normal training.

"The fact the U.S. military put so much effort into searching for a single SDF aircraft shows that it contained a high concentration of military secrets," said a government source in Tokyo.

The aircraft went down in open seas, which means Japan could have done nothing if Russia and China had beaten it to the punch and found any part of the F-35A.

Those two nations consider the stealth aircraft a major threat and would have liked nothing better than to get their hands on whatever technological information they could.

"Because Russia and China are competing with the United States to develop an advanced fighter jet, they would do anything to get their hands on F-35A technological information," a high-ranking SDF officer said. "It is possible to extract secret information even from a single part of a small fragment."

While the Defense Ministry announced May 7 that some debris had been recovered, it came about a month after the April 9 crash.

The ASDF deployed a rescue helicopter and a search-and-rescue aircraft to locate the stealth fighter, and the Maritime SDF mobilized a number of vessels to the crash site.

The Defense Ministry asked the Japan Agency for Marine-Earth Science and Technology to dispatch an underwater research vessel to the site. The research vessel used sonar to detect parts of the F-35A on the seabed at a depth of about 1,500 meters.

The U.S. Navy chartered a private-sector underwater support vessel to handle the retrieval of aircraft parts.

The ships and aircraft used by the SDF and U.S. military searched the waters on a daily basis. The B-52 bomber may have been dispatched to conduct surveillance against any moves by Russia and China to join in the hunt.

Another reason for the extensive search is that the cause of the crash will not be known unless the rest of the aircraft is recovered.

And that investigation could also have an impact on future purchases of the F-35 from the United States. The government plans to acquire a total of 147 stealth jets in two main models. The F-35A is only capable of conventional take-off and landings, but the F-35B can take off from short runways, like those on aircraft carriers, and land vertically.

At an April 19 news conference after meeting with U.S. officials, Defense Minister Takeshi Iwaya said there was no change in the government's plans to acquire the F-35.

But if mechanical problems with the aircraft are determined as the cause of the first-ever crash of the F-35A, future procurements could be affected not only for Japan, but the 12 other nations that have also expressed interest in purchasing the fighter.

In June 2018, the U.S. Government Accountability Office released a report pointing to 966 technological problems with the F-35, including the life-support system. That led to six cases between May and August 2017 of pilots reporting symptoms of oxygen deprivation.

Because of the lengthy process to determine the cause of an aircraft crash, there are no indications yet of when F-35A flights by the ASDF will resume.

There are also concerns that the final assembly of the F-35A at the Mitsubishi Heavy Industries Ltd.'s plant in Toyoyama, Aichi Prefecture, may have contributed to the accident. The aircraft was the first assembled at that plant under a licensing contract signed with Lockheed Martin Corp. of the United States.

There are plans for joint international development of the next-generation fighter jet to replace the F-2.

"If it turns out that not even final assembly can be done competently, criticism will arise that Japan is not fit to lead the development process," said a high-ranking Defense Ministry official.

(This article was written by Takateru Doi and Taketsugu Sato, both senior staff writers.)