Japan has approved the supply of missile interceptor parts to the USA and the transfer of sensor-related technology to Britain.
The announcement marks the first major deals since Tokyo eased a ban on arms exports in April as part of steps taken this year by Prime Minister Shinzo Abe to lift some of the constraints Japan's pacifist constitution imposed on its security policy, which also ended a ban that has kept the military from fighting abroad.
The Japanese government gave the green light to the export of gyroscopes used to help US-developed Patriot Advanced Capability-2 (PAC-2) missile interceptors tail their targets precisely.
Japan's decision comes after the US said on Monday signed an agreement with Qatar to sell the Gulf state Apache attack helicopters and Patriot and Javelin air-defence systems valued at $11bn.
Mitsubishi Heavy Industries, Japan's top defence contractor, manufactures the gyroscopes under license from Raytheon, US maker of defence electronics, while production lines have been shut in the US, the Defence Ministry said.
"I believe by providing these components, our relations with the US will improve further," a Defence Ministry official said at a briefing.
Japan also gave the nod to supplying sensor technology to Britain as part of planned joint research aimed at boosting air-to-air missiles' guiding capabilities, a project with potential applications for the F-35 stealth fighter and other combat aircraft.
Besides defence authorities from both countries, Mitsubishi Electric is likely to participate in the project from the Japanese side, and MBDA on the British side, the Defence Ministry official said.
MBDA is a pan-European company formed more than a decade ago from the missile units of BAE Systems, Airbus and Finmeccanica.
Global orders for Lockheed Martin's F-35, the world's most expensive weapons project with a price tag of about $400bn, are expected to exceed 3,000, with the first shipment to Japan slated by March 2017.