Despite assurances from Japan that its military would be able to intercept North Korean missiles fired at Guam, analysts believe there is little chance that an attack on the Pacific island by intercontinental ballistic missiles could be thwarted.
Speaking in the Japanese parliament on Thursday, Itsunori Onodera, the defence minister, said Tokyo would come to the assistance of the United States and any other allies in the event of an attack.
“We are always prepared to deal with emergencies”, he said, after North Korean state media detailed plans to launch four Hwasong-12 intermediate-range missiles over the Japanese prefectures of Hiroshima, Shimane and Kochi en route for Guam.
The defence minister’s comments were echoed by Yoshihide Suga, the chief cabinet secretary, who told a press conference, “We cannot tolerate such a clear provocative act to the security of the region and international society, including out country.
“We will maintain our monitoring and surveillance at a high level and take all possible means to cope with any situation”, he said.
Japan and the US have both deployed destroyers equipped with the Aegis ballistic missile defence system, using SM-3 Block 1A and 1B interceptors, in the Sea of Japan to target short and intermediate-range ballistic missiles. The weapon is intended to destroy offensive missiles in the middle stage of their course.
The system is backed up on land by the Patriot PAC-3 anti-missile system, which has been deployed at Japanese and US military facilities around Japan, as well as in the grounds of the Defence Ministry in Tokyo.
Neither system is presently capable of effectively countering an ICBM launched on a lofted trajectory towards Guam.
In a report on the 38 North web site, operated by the US-Korea Institute at Johns Hopkins University, analysts concluded that the likelihood of Aegis destroyers downing an ICBM test or offensive launch is “limited, if not improbable”.
“In fact, the probability that the North Korean ICBM test will fail on its own is significantly higher than the probability of success”.
“The United States and Japan operate Aegis ships armed with SM-3 Block 1A and 1B interceptors in the East Sea,” the report stated. “These ships are capable of intercepting short, medium and intermediate range ballistic missiles in the mid-course and terminal phases of flight.
“Tests to validate the performance of the SM-3 Block 1 interceptors are ongoing and to date have been largely successful”, it adds. “SM-3 interceptors have never been tested against an ICBM, nor have they been tested against any missile in the boost or ascent phase of flight. “In other words, boost – or ascent phase intercepts using SM-3 interceptors are an unproven, hypothetical capability.”
Consequently, Aegis warships can only intercept a North Korean ICBM in a “limited set of circumstances”, such as the weapon flying on a low trajectory that comes within 310 miles of a destroyer.
North Korea’s recent launches, however, have been on steeply lofted trajectories that will rapidly take them beyond the range of interceptors.
Even if the US was fortunate – North Korea launched a missile directly over an Aegis ship and the trajectory was not sufficiently lofted – it is still doubtful that a successful intercept would occur, the report states.
First, it is doubtful that an Aegis ship would be close enough at the right time, it adds, pointing out that: “The US or Japan would be placing their Aegis boats at considerable risk if either attempted to move closer than 200 km [125 miles]off North Korea’s coast while waiting for a launch.”
Secondly, it remains “unclear” whether the necessary tracking data can be acquired with sufficient precision and for a fire-control solution to be developed in the 10 seconds after the launch is detected.
The study concludes that “Sea-based missile defenses available today are not capable of reliably interrupting a North Korean ICBM test”.