Jan. 25 (Bloomberg) -- Japan now hosts U.S. surveillance technology that can detect missile launches in North Korea or elsewhere in the region, enhancing its ability to defend against attacks.

The Joint Tactical Ground Station, newly deployed at Misawa Air Base in northern Japan, receives data directly from satellites that detect missile attacks, according to U.S. officials at the Jan. 22 unveiling of the so-called JTAGS unit.

Japan was already in the loop to receive alerts from U.S. installations that monitor surveillance satellites watching for missile launches, and an identical JTAGS facility in South Korea. The unit at Misawa transmits data to Japan's top command and the U.S. Pacific Command, reinforcing the communications links needed to bring defensive weapons into action.

Deploying the JTAGS technology in Japan adds useful ``redundancy,'' said Brigadier General John E. Seward, deputy commander of the Space and Missile Defense Command, based in Colorado Springs, Colorado.

Should an attack be detected, Japan would have to defend itself unless a U.S. Navy Aegis-equipped warship was in position to destroy incoming missiles, Seward said. The only U.S. missile defenses in Japan are Patriot Advanced Capability 3 (PAC-3) ground-to-air missile batteries deployed in Okinawa to protect U.S. forces there.

Japan has acquired land-based PAC-3 missiles, and this month conducted communications experiments in central Tokyo with the idea of deploying them in the city.

Aegis Destroyers

Japan is also equipping four of its Kongo-class destroyers with the U.S.-developed Aegis Ballistic Missile Defense system, which combines online radar and missile-intercept technologies. The first ship to deploy the equipment intercepted a ballistic missile in a December test.

U.S. officials at Misawa praised Japan's cooperation in the four-year project to deploy JTAGS, in contrast to the reluctance of European countries including Poland and the Czech Republic to participate in U.S. missile-defense proposals.

``Japan is one of our strongest allies in ballistic missile defense,'' Seward said. ``I know that Japan has a higher interest. They have had some incidents with their neighbors. They're concerned about it.''

A North Korean missile would have flown over Japan to a spot in the Pacific Ocean near Hawaii in July 2006 if it hadn't fallen apart shortly after launch. North Korea claimed the incident was merely a satellite launch. Japan disputed that claim.

In October the same year, North Korea staged a nuclear test explosion. The communist country's ideology singles out former colonial master Japan as a particular enemy.

Thwarting Attacks

Japanese defense officials have made clear that the only country ever attacked with nuclear weapons won't feel secure relying solely on the U.S. ``nuclear umbrella'' of assured retaliation for deterrence. Japan wants to be able to thwart any missile attack.

Ballistic missiles generate heat that can be detected during the launch phase by infrared surveillance. The tracking must be rapid because the rocket engine typically burns out after about 90 seconds after which the missile is coasting, Tokyo-based armaments consultant Lance Gatling said in an interview.

Those seconds are enough for ground data systems such as JTAGS to calculate the trajectory and determine roughly when and where the missile will impact, Gatling said. With the data, target areas can be alerted and attacks to take out launch sites and prevent repeat attacks can be ordered.

Trajectory data can also be relayed to radar units. Unlike satellites, which can track only the exhaust heat, radar can lock onto the missile itself and further pinpoint its trajectory, giving missile-defense weapons a chance to knock it down, Gatling said.

Developed in response to battlefield commanders' need for more information on incoming SCUD missiles during the Gulf War, the JTAGS technology is deployed at four sites around the world. The others are in Stuttgart, Germany; Qatar; and Osan, South Korea.

To contact the reporter on this story: Bradley K. Martin in Tokyo at bmartin18@bloomberg.net or

Last Updated: January 24, 2008 21:27 EST