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TOKYO — Nothing exposes the toothlessness of Japanese foreign policy quite like a bit of saber rattling on the Korean peninsula.

North Korea's launch of seven ballistic missiles into the Sea of Japan on July 4 have certainly raised fears here. The Pyongyang regime's choice of the U.S. independence holiday for its biggest single-day barrage of missiles in three years shows the display of military might was a message intended for Washington.

Tensions in Japan have been high since North Korea conducted an underground nuclear test on May 25, weeks after it test-fired a long-range rocket that flew over the Japanese archipelago before splashing harmlessly into the Pacific Ocean.

The trajectory of that missile is justification enough, Tokyo says, for treating every...