to think about distances and air force strength in Northeast Asia,” said Hideshi Takesada, a professor of international relations at Seoul’s Yonsei University. “This decision reflects the need for stealth and long-distance combat capabilities.”

Japan’s fleet of fighter jets totalled 362 at the end of the last financial year and the new generation fleet of radar-evading F-35s will replace Boeing F-4s, which were last assembled in 1981.

The F-35 was initially shortlisted by the government alongside the Eurofighter Typhoon, which BAE Systems manufacturers alongside EADS and Finmeccanica, and also Boeing Co.’s F-18 Super Hornet.

However, experts had widely predicted that Japan would most likely opt for F-35 due to its sophisticated stealth capabilities combined with its origin in the US, a close defence ally of Japan.

The current security instability in the Asia-Pacific region, where concerns are focusing on the future of the unpredictable North Korean regime in the hands of Kim Jong-il’s young son, is likely to fuel further US arms sales in coming years, experts have forecast.

Richard Aboulafia, vice president of analysis at Teal Group, an aerospace industry consultancy, said: “Northeast Asia is a difficult neighbourhood, and the situation just got even more complicated and uncertain. That's probably good for arms sales, particularly for US companies that benefit from the strategic relationship factor."