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Mitsubishi Heavy Industries, Japan's leading defense contractor, produced a prototype stealth fighter known as the
X-2 in 2016 as part of the Advanced Technology Demonstrator-Experimental (ATD-X). However, the $350 million price tag of
that program led the defense ministry to seek other options.

つまりX-2作ってみたけど、そこで自らの技術力や能力の限界を知り、アメリカイギリスに助けを求めている
ということなのか。