By Tim Kelly and Nobuhiro Kubo
TOKYO (Reuters) - U.S. defence contractor Lockheed Martin Corp (LMT.N) plans to offer Japan a stealth fighter design based on its export-banned F-22 Raptor and advanced F-35 Lightning II aircraft, two sources said.
Lockheed has discussed the idea with Japanese defence ministry officials and will make a formal proposal in response to a Japanese request for information (RFI) after it receives permission from the U.S. government to offer the sensitive military technology, said the sources, who have direct knowledge of the proposal.
The decision on whether to release parts of the highly classified aircraft designs and software to help Japan stay ahead of Chinese advances will test President Donald Trump's promise to overhaul his country's arms export policy.
The proposed aircraft "would combine the F-22 and F-35 and could be superior to both of them," said one of the sources.
Japan, which is already buying the radar-evading F-35 to modernise its inventory, also wants to introduce a separate air superiority fighter in the decade starting 2030 to deter intrusions into its airspace by Chinese and Russian jets.
The country's air force currently flies the F-15J, based on the Boeing F-15; and the F-2, based on the Lockheed Martin F-16. Both designs are decades old.
Japan's ambition to build its own stealth fighter was in part spurred by Washington's refusal a decade ago to sell it the twin-engined F-22, which is still considered the world's best air superiority fighter.
Although the Japanese stealth aircraft programme, dubbed the F-3, was conceived as a domestic effort estimated to cost around $40 billion, Tokyo has recently sought international collaboration in a bid to share the expense and gain access to technology it would otherwise have to develop from scratch.
Any aircraft built with international partners must have Japanese-designed engines and radar, however, and feature other components made locally, the other source said. Mitsubishi Heavy Industries <7011.T> tested a prototype stealth jet in 2016 that cost the Japanese government $350 million to develop.
"We are considering domestic development, joint development and the possibility of improving existing aircraft performance, but we have not yet come to any decision," a Ministry of Defense spokesman said on Friday.
The Japanese government in March issued a third RFI for the F-3 to foreign defence companies and sent a separate document outlining its requirements in more detail to the British and United States governments.
In addition to a proposal from Lockheed, Japan is hoping for responses from Boeing Co (BA.N), which makes the F/A-18 Super Hornet multirole fighter, and BAE Systems Plc (BAES.L), which is part of the consortium that built the Eurofighter Typhoon high-altitude interceptor.
"We look forward to exploring options for Japan's F-2 replacement fighter in cooperation with both the Japanese and U.S. governments. Our leadership and experience in 5th generation aircraft can be leveraged to cost-effectively provide capabilities to meet Japan’s future security needs," a Lockheed Martin spokeswoman said.
Boeing and BAE did not immediately reply to requests for comment.
Japan's last jet fighter, the F-2, which entered service in 2000, was built jointly by Mitsubishi Heavy and Lockheed Martin. As Japan's leading fighter maker, MHI, which built the World War Two-era A6M Zero, would anchor the Japanese portion of any new project.
(Reporting by Tim Kelly and Nobuhiro Kubo; Editing by Gerry Doyle)