The Joint Chiefs of Staff are following a Navy recommendation to buy American-made SM-3 interceptor missiles for Aegis ships.
The SM-3 missile is capable of intercepting an incoming enemy ballistic missile at an altitude of 150 km, much higher than the ground-based PAC-3 missiles now in use.
The Navy recommended the purchase because the new PAC-3 system has a high failure rate because it leaves only 5 to 7 seconds to intercept North Korea's Scud or Rodong missiles.
A government source said the SM-3 missiles can be deployed on the Aegis ships like the Sejong the Great once the Navy's software is upgraded.
South Korea has only an improved version of the Patriot PAC-2 missile and has been eyeing a better version, the PAC-3.
One SM-3 missile costs W15 billion (US$1=W1,104), seven times as much as the PAC-3. SM-3s are a key component of the U.S. missile defense system, but experts question whether they would be suitable against North Korean missiles, which fly at a low altitude over short ranges.
During a visit to South Korea, China, and Japan recently, Gen. Martin Dempsey, the chairman of the U.S. Joint Chiefs of Staff, said, "Now is the right time, with the right capabilities in place, to seek to establish a collaborative, trilateral ballistic missile defense architecture incorporating U.S., Japanese and South Korean military assets."
He also proposed that "senior military officers of all three countries advise their political leaders to integrate air and missile defense systems."
This spawned speculation that the U.S. is trying to deploy its own SM-3 missiles in South Korea following their deployment on the U.S. mainland and in Japan.
South Korea is pushing for its own defense system against ballistic missile attacks from the North rather than joining the U.S. shield.
"There are some historic sensitivities," Dempsey said, referring to suspicions in South Korea and China against Japan over its past aggression. But he added, "All three nations should be mature enough to set aside their differences and focus on the common, prolonged threat of ballistic missiles from Pyongyang."