Britain and Japan are close to an agreement to merge their next-generation Tempest and F-X fighter jet programs, with the two countries aiming for a deal on a new joint project by year-end, three sources told Reuters.

It would be the first time Japan has sought a non-U.S. partner for a large military program and the first major collaboration between Tokyo and London, going beyond what had been expected when industrial talks began five years ago.

“This would be an equal partnership between Japan and Britain,” said one of the sources with knowledge of the plan. It will cost tens of billions of dollars, he added.