Included would be new brains for the Aegis system’s radar, designed to be able to thwart ballistic missiles at the same time as defend against other airborne attacks.

Also included would be new computing infrastructure, displays, consoles and sensors, Bucci said from Huntsville, Alabama, where he was attending an Army-supported conference on space and missile defense.

With such a modernization, the Atago and Ashigara would be capable of firing an updated SM-3 missile that Japan is co-developing with the United States. Kongo-class destroyers would need a separate upgrade of their own to achieve this.

The updated SM-3 interceptor, known as Block IIA, is a cornerstone of the penultimate phase of President Barack Obama’s roadmap for defending NATO’S European territory against missile attack.

The interceptor’s larger rocket motors and advanced “hit-to-kill” warhead are meant to defend a greater area. The warhead works by colliding with its target. The program is on track for a 2018 delivery, Raytheon, the U.S. partner, said in March. Mitsubishi Heavy Industries Ltd is the Japanese contractor.

The cooperative research effort on the updated interceptor been carried out under a U.S.-Japanese memorandum of agreement signed shortly after North Korea’s surprise Aug. 31, 1998, launch of a three-stage Taepo Dong-1 missile that overflew Japan before falling into the Pacific.

Bucci in the interview said he was “pretty sure” that South Korea, which has three Aegis-equipped destroyers, has been talking to the U.S. Navy about similar ship upgrades to ballistic missile defense configuration.

The U.S. Defense Department and the Navy had no immediate comment on any such possible programs for Japan or South Korea.

The U.S. Navy’s own fleet of ballistic missile defense-capable Aegis ships is schedule to grow from 24 at the end of fiscal 2011 to 36 by the end of fiscal 2018, according to an August 10, 2012, report by the nonpartisan Congressional Research Service, a Library of Congress arm.