In December, 2003, the Japanese Government had approved the adoption of the Patriot Advanced Capability 3 (PAC-3) missile system, as well as the stationing of a US Navy AEGIS/Standard Missile-3-equipped combatant off Japans coast. The first such Long-Range Surveillance and Tracking (LRS&T) platform, in the form of an American guided missile destroyer, took up position off Japan in October of 2004. At that time Japan was already on record as being very concerned about North Koreas continuing nuclear weapons and missile programs. The current deployment is the first part of a three-phase defense approach. Phase two is to occur in 2005 with the outfitting of up to seven additional US Navy ships with Standard Missile-3 Block-1 missiles to counter both short- and medium-range ballistic missile threats. The last phase is to occur in 2006, when the Navy is to have 10 - 15 destroyers and cruisers dedicated to carrying-out ballistic missile defense operations against any likely threats.
Plans also include for missile activity data monitored by the ships to be transmitted to Fort Greely, AK, and Vandenberg Air Force Base, CA, both of which would coordinate in the launch of ship-based and land-based interceptor missiles.
The decision by Japan is an attempt to loosen other constraints built-into its defense doctrine. For example, Japan is currently barred from collective self-defense with its neighbors, so as it now stands it could not lawfully intercept a missile aimed at an allied country.
Japan is already within the range of Pyongyangs existing missiles, such as the No-Dong, which would reach Japan just ten minutes after launch from North Korea. In 1998, North Korea sent a missile over Japan, taking both Japan and the US by surprise and helping instigate the current set of US-Japan defense proposals. K.B. Sherman
A few months ago Japanese military planners proposed changing the military regulation to to increase the speed with which the JSDF (Japanese Self-Defense Forces) could respond to a missile attack from another country. Under current law, members of the Cabinet and Japan's Security Council must approve a JSDF mobilization, which must then be ordered by the prime minister. A possible remedy for this problem would be to allow the prime minister to give prior approval for subsequent fast action by the JSDF to combat a missile attack. In this scenario, the prime minister would already have been given warning that such an attack was likely. This change would have the potential to decrease Japans response time from as long as several days to a matter of minutes.