Aegis destroyers and ballistic-missile defense

Japan's Aegis-equipped destroyers developed through successive designs from the Kongo class to the Maya class, with eight ships in this family. Later purchases in pairs provided incremental growth and a politically workable compromise. The two planned Aegis System Equipped Vessels would add ballistic-missile-defense capacity. The case for four rests on the assessment that Japan needs greater numbers in an increasingly armed and assertive neighborhood. A further pair remains a possibility, and that sequence would fit Japan's procurement precedent.