The failure of North Korea's much-publicized rocket launch on April 13 occurred as Japan readied its ballistic missile defense (BMD) force to destroy the rocket if it fell toward its territory. The launch, which North Korea claimed would loft a satellite, could have provided a rare opportunity for Japan to collect data on the North Korean missile, against which Japan's BMD system was conceived in the 1990s.

Japan's interest in missile defense dates to 1966, when it requested information from the U.S. “for use in planning antimissile defenses” against China for the 1972-77 period. Nothing concrete came of the request, since the Japanese were largely interested in information-gathering. However, as early as 1968, government officials assessed there would be no constitutional impediment to Japanese acquisition of a missile defense system because it could be justified as a defensive weapon.

Throughout the 1970s and 1980s, interest in missile defense remained dormant as Japan saw neither China nor North Korea as major threats. But Iraq's Scud missile attack on Israel in the 1991 Persian Gulf war and North Korea's Nodong missile test in 1993 renewed interest, leading to a comprehensive study in 1995. North Korea's overflight of Japan with a Taepodong-1 missile in 1998 jolted Japan into action.

The first concrete measure taken was the decision to develop Mitsubishi Electric's FPS-5 air-search radar as the early warning component of the BMD system, which was neither clearly defined nor authorized in 1998. Detection and tracking of ballistic missiles was added as a requirement for the FPS-5 after the North Korean overflight. The government decided to field the BMD system only in December 2003, putting together sensors and weapons that were being separately developed and procured.

The FPS-5, nicknamed Gamera after a turtle-like monster in Godzilla movies, is an 1,800-ton, 34-meter-high (111.5-ft.), three-face rotating radar. One 18-meter dual L/S-band active phased array detects and tracks ballistic missiles over 1,000 km (620 mi.) away, while two 12-meter, L-band active phased arrays deal with aircraft. The first FPS-5 site, off the southernmost main island, went operational in April 2009, in time for the second overflight of Japan by a North Korean missile. Four sites had been built by late 2011, and the defense ministry ordered one radar set at a cost of ¥11 billion ($136 million) last year. The FPS-5 could be viewed as Japan's equivalent of America's Pave Paws radar.

Another indigenous element of the BMD system is the Japan Aerospace Defense Ground Environment (Jadge) supplied by NEC. When development of Jadge—the brain of the BMD system —began in 2002, dealing with ballistic missiles was not a requirement. That capability was added in 2004 to the system design, which uses many pieces of commercial off-the-shelf hardware. Jadge was delivered in 2007, and went operational in 2009.

The BMD system's two “fists” are Raytheon SM-3 Block IA interceptors in four Kongo-class Aegis destroyers and ground-based Raytheon PAC-3 batteries. The Kongos, built in the 1990s as area-air-defense ships for four antisubmarine warfare flotillas, underwent conversion from 2004-10 to Aegis BMD ships. All four test-fired SM-3 Block IAs from 2007-10, scoring three hits in four attempts. Until 2008, Japan bought 36 SM-3 Block IAs, nine each for four ships. Four test shots left 32 for defense.

Japan has worked with the U.S. on development of the SM-3 Block IA from 1999, as well as on the advanced SM-3 Block IIA, which will cover a wider area thanks to a bigger booster. With the Block IIA, only one Aegis ship will be required to cover all of Japan in contrast to two ships using the older interceptor. Two new Atago-class Aegis destroyers commissioned in 2007-08 will undergo conversion to Aegis BMD ships, bringing the total to six, which will allow permanent deployment of at least two at sea. Mobile PAC-3 batteries, which will increase to six from three, are used as point-defense missiles. Mitsubishi Heavy Industries produces the PAC-3 under license.

The defense ministry's Technical Research and Development Institute believes Japan should be self-sufficient in weapons as well as in sensors and battle management to ensure long-term sustainability of the BMD system. R&D projects for that goal may include new airborne sensors for Japan's Boeing E-767 replacement in the late 2020s and a missile to replace the PAC-3 in the 2030s.