The United States and Japan are discussing system upgrades for a pair of Japanese destroyers to boost defenses against a ballistic missile attack, an executive at the Pentagon’s top contractor said Wednesday.

The potential multimillion-dollar updates to two Atago-class guided-missile destroyers would provide cutting-edge “Aegis” ballistic missile defenses equivalent to those being added to U.S. Navy ships, said Nick Bucci, who heads such maritime programs at Lockheed Martin Corp.

Japan, rattled by North Korean nuclear arms and ballistic missile tests, has emerged as the most important U.S. partner in crafting a layered shield against missiles of all ranges and in all phases of flight.

The United States has been spending roughly $10 billion a year on the overall project, a reflection of concern chiefly about North Korea and Iran.

Lockheed Martin’s Aegis combat system weaves in radar, computers, software, displays, weapons launchers and weapons to defend against a range of surface, aerial and underwater threats.

Named for the mythological shield of Zeus, the Aegis system is to be deployed ashore in Romania and Poland starting around 2015 to defend Europe from ballistic missile threats from countries such as Iran, as well as on a growing number of U.S. ships.

Japan decided in 2003 to upgrade all four of its Aegis-equipped Kongo-class destroyers to be capable of shooting down ballistic missiles using Raytheon Co Standard Missile-3 interceptors.

The work now under discussion would modernize the Aegis systems aboard the Japan Maritime Self-Defense Force’s Atago and Ashigara to a more advanced setup than the Kongo-class, Bucci said in a telephone interview with Reuters. He declined to cite a potential value for such upgrades other than millions of dollars.

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.