Japan is preparing to deploy a missile defence system against a North Korean rocket launch in what could be the first use of a “Son of Star Wars” system to knock out an intercontinental ballistic missile.

The Government plans to dispatch naval destroyers equipped with anti-missile systems to the seas off North Korea as the isolated dictatorship prepares for the launch of a rocket. The move could have strategic implications for the whole of northeastern Asia. As long as the weapon passes through the atmosphere far above Japan, as seems to be the intention, the system will probably not be fired. If the North Korean rocket malfunctions and threatens any of its islands Japan will become the first nation to use a long-range missile defence system outside a test.

“If it is capable of reaching Japan then it goes without saying that we will react,” Yasukazu Hamada, the Japanese Defence Minister, said yesterday. “We have been making preparations, including ballistic missile defence, for any incident which could affect Japan. If it will affect Japan then it will be our target.”

The Japanese Kyodo news agency said yesterday that the destroyers Kongo and Chokai will be sent to the waters that separates the two countries. Both are equipped with SM3 missiles designed to intercept an incoming ballistic missile after it has passed beyond the atmosphere and into space. The political and strategic risks of such an attempt are very high.

If Japan tries and fails to take out a North Korean rocket it will be an international humiliation and a crushing blow to the expensive missile defence programme, which is already expected to surpass its estimated cost of as much as $8.9 billion (£6.3 billion) by 2012. If it succeeds it will rattle China, which already fears that the combined US-Japan missile defence effort will undermine its own limited nuclear deterrent.

It will also enrage North Korea, which loathes what it still demonises as “Imperial Japan”, and insists that the rocket being prepared at its Musudan-ri launch site in the northeast of the country is not a weapon but the vehicle for the launch of a peaceful communications satellite.

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