Japan has selected Lockheed Martin [LMT]’s F-35 as its next generation fighter, giving the beleaguered Joint Strike Fighter program a major boost and an opening to additional foreign sales.

The Japanese Defense Ministry announced recently that F-35 Lightening II had won the competition over Boeing‘s [BA] F/A-18 and Eurofighter‘s Typhoon. Lockheed Martin will build 42 of the planes with delivery starting in 2016 at a unit cost of 9 billion yen ($115 million), including spare parts.

Japan’s purchase of the multi-role stealth fighter further tightens military relations with the United States, which envisions the F-35 as its main fighter jet of the future. It will enhance interoperability between the two militaries and possibly in the Asia Pacific, with Australia in line to get the planes and South Korea expected to soon announce its next generation fighter. Japan’s decision comes amid a Chinese military buildup and as an isolated North Korea undergoes a leadership transition.

Observers believe Lockheed Martin could have the upper hand in the South Korea competition following Japan’s decision as other countries were closely monitoring Tokyo’s move.

“We have capacity and tooling to meet that requirement and we also have capacity and tooling and meet other countries requirements as well, in addition to Korea,” said Steve O’Bryan, Lockheed Martin’s vice president for program integration and business development for the F-35.

The U.S. program is the largest in Pentagon history at price tag of $382 billion for more than 2,200 of the aircraft jointly developed for the Air Force, Navy and Marine Corps. Japan selected the Air Force’s F-35A variant. Despite the international interest in the plane, the Joint Strike Fighter program has been under heavy scrutiny in Washington because of massive cost overruns and production delays. Some members of Congress have suggested cancelling it.

The appropriations bill Congress passed this month cut $151 million in a Pentagon request for the F-35A in the fiscal 2012 budget. The bill further cut $94.5 million in advance procurement for the Air Force variant and $109 million for the Navy’s F-35B.

The first four Japanese F-35s will be built at Lockheed Martin’s Fort Worth, Texas plant. The components, including the wings and forward fuselage, for the remainder of the fleet will be built in Fort Worth and final assembly will take place in Japan, O’Bryan said.

“The components will still be built in Fort Worth and would be shipped for final assembly,” he said, adding he expected the Japanese buy will contribute to 10,000 direct and indirect jobs in the United States.

Japan required bidding firms to outline plans for bringing work and technology sharing to the country’s defense industry.

“We have offered a final assembly and checkout facility, which is really a production line in Japan, and we have offered component and subcomponent builds in Japan as well,” he said. Engine maker Pratt and Whitney has offered final assembly check out in Japan, he said.

Japan will benefit from advanced composites used in the plane, automated machining, advanced avionics and advanced propulsion systems they don’t have on fourth generation fighters built in Japan in the past, O’Bryan said.

Japan is buying the F-35 to replace its aging fleet of F-4s and the program could be expanded if the country decides to recapitalize its F-15s.

The Joint Strike Fighter has been developed by primary partners the United States and United Kingdom, along with tier two and three developing partners Italy, Netherlands, Turkey, Canada, Australia, Denmark and Norway.

Italy and Australia are to begin receiving the jets in 2014, with arrivals expected in Turkey and the United Kingdom in 2015, following by Norwegian, Israeli and Japanese jets in 2016.

“We’re highly confident in delivering the Japanese jets on time,” O’Bryan said.