WASHINGTON — In a key milestone for the international program, the first Japanese-built F-35 joint strike fighter began its assembly today at a facility in Nagoya, Japan.

The aircraft, known as the AX-5, officially began the "mate" process today when its wings, fuselage and tails joined together for the first time to form the structure, the joint program office said in a Dec. 15 statement.

AX-5 is the first F-35A assembled in Japan and will join the Japanese Air Self-Defense Force fleet in 2017.

The first four of Japan's planned 42 planes are in various stages of production at Lockheed Martin's F-35 facility in Forth Worth, Texas. The first, AX-1, is slated for delivery in 2016.