Whether or not to send an Aegis destroyer to the Indian Ocean has been a touchy question ever since Japan indirectly joined in the U.S. military campaign in Afghanistan about a year ago. The question was settled, officially at least, earlier this week when the government decided, after hemming and hawing, to dispatch the high-tech warship around the middle of this month.

The decision marks a step forward in Japan's expanding logistic support of U.S.-led antiterrorism operations. Up till now, however, an Aegis dispatch had been shelved on grounds that Japan might get involved in a collective military operation prohibited by the Constitution.

The destroyer's air-defense system, whose radar can track objects up to several hundred kilometers away, is capable of simultaneously striking more than 10 targets. Data collected by the vessel would be shared with U.S. forces. If such data is used as the basis for a U.S. attack, the argument goes, it could both constitute an exercise of the right to collective self-defense and result in the destroyer becoming a combat target.