PHILADELPHIA — Once again the issue of Japanese contributions to international security efforts is the subject of tortured debate. And once again the proposed government policy, and aspects of the debate itself, reveals fundamental misunderstanding of the relationship between Article 9 of the Constitution and the relevant principles of international law.

This time, the issue relates to maritime piracy off the coast of Somalia, and the proposed deployment of Japanese naval vessels to the area. Predictably, the issue has triggered debate over the effect of the war-renouncing provision of the Constitution. A careful analysis, however, would suggest that the Article 9 prohibition on the use of force would not apply to the deployment of naval forces,...