The gas turbine parts manufactured by Kawasaki Heavy Industries will be produced for Rolls-Royce which will then supply them to the Royal Navy, the business daily Nikkei and Kyodo News said.
The government said the parts were not deemed weapons as they are used in civilian aircraft and emergency generators as well as naval ships, the reports said.
No official was immediately available for comment at Kawasaki Heavy on Monday, a public holiday.
The Japanese firm, a long-term technical cooperation partner of Rolls-Royce, has been manufacturing the engine parts in Japan for the Japanese naval defence force and other users under license from the British firm, Kyodo said.
Rolls-Royce has stopped making the components for the Royal Navy but replacements were needed, so it ordered them from Kawasaki Heavy, the reports said.
The Royal Navy asked Japan’s naval defence force to study whether the export of the parts would contravene Japan’s policy against arms sales, Kyodo said.
Tokyo is looking to increase exports of such dual-use technology, which would help Japan’s defence industry boost output and reduce production costs, Nikkei said.
Such exports can also help Japan forge stronger defence ties with friendly countries, it added.
Under a policy adopted in 1967 and tightened in 1976, Japan has prohibited weapons sales to communist states, countries subject to embargoes under UN resolutions and nations involved in international conflicts.