In addition to the interceptors, Mr. Hagel mentioned Pentagon plans to install a second advanced radar system in Japan to more quickly detect North Korean missile launches.

WSJ: U.S. to Boost Missile Defenses in Response to North Korea

Mr. Hagel also outlined a series of upgrades under development, including plans to install a second advanced radar system in Japan to more quickly detect North Korean missile launches.

WSJ: U.S. to Boost Missile Defenses in Response to North Korea

It also carries the advanced AEGIS air defence system that is rapidly becoming the backbone of US naval radar.

BBC: News | In Depth | Military Fact Files