The UK now owns 17 F-35B Lightning stealth fighter jets, and Defence Secretary Gavin Williamson has pledged that a total of 138 will be bought.
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 US security.
The F-35 was less than a year old and was delivered to the ASDF in May last year, he added.
Japan selected the F-35A as the JASDF's next-generation fighter aircraft in December 2011 with an initial order for 42 F-35As.
The Defense Ministry has suspended flights of all remaining F-35As at the Misawa Air Base for the time being.
Iwaya added, "I want to express my deepest apologies for giving local residents a great deal of anxiety".
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The crash was only the second time an F-35 has gone down since the plane began flying nearly two decades ago. It is made by Lockheed Martin, but the crashed plane is the first to be assembled in Japan by Mitsubishi Heavy Industries in Nagoya, Japan. Each costs around $100 million, slightly more than the cost of buying a fully assembled plane.
Peter Layton, a former Australian Air Force officer and analyst at the Griffith Asia Institute, said the Japanese assembly line would be one of the first places to look for answers.
According to the Defense Ministry, the missing pilot was a seasoned veteran with about 3,200 hours of flight experience including about 60 hours of flying an F-35A.
The aircraft crashed in waters that reach a depth of around 1,500 meters, making recovery, particularly of the aircraft's flight data recorder, difficult, the official said.
The aircraft was one of four Japanese-flagged F-35s conducting training operations roughly 83 miles east of Misawa Air Base at the time of its disappearance.
He was flying what is considered the best stealth jet technology in the skies.With the world's most advanced avionics, engines and weaponry, the Pentagon touts the F-35 as the "the most affordable, lethal, supportable and survivable aircraft ever to be used".
The aircraft, created to penetrate enemy defences by evading radar detection, was delivered to the ASDF in May a year ago, the ASDF spokesman said.