On December 2, Reuters published an article claiming U.S. congressman Mike Rogers and Adam Smith had both suggested that the Pentagon was considering installing Terminal High-Altitude Air Defense (THAAD) batteries to two sites on the West Coast to protect against attack by North Korean intercontinental ballistic missiles (ICBMs).
The United States is already shielded by the Ground-based Midcourse Defense system , with launch sites in Alaska and California that can fire huge missiles to intercept ICBMs in space. However, the GMD system currently has only a limited supply of forty-four, and has only hit its target in slightly over half of tests.
By contrast, THAAD is designed to smack down missiles as they plunge on their targets in the terminal phase of their trajectory, and has not failed a single interception test.
However, the deputy director of the Missile Defense Agency subsequently stated it had “received no tasking” for West Coast THAAD sites, and later Rogers appeared to deny making the claim .
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It so happens that there’s a little problem with deploying THAAD to the West Coast: nearly all sources agree it’s designed to shoot down short- and intermediate-range ballistic missiles, not ICBMs.
THAAD vs. ICBM
A ballistic missile in its terminal descent phase offers an interceptor system only a very small window in which it can be shot down before it detonates its warhead. A THAAD interceptor flies at Mach 8—more than three times the speed of a rifle bullet—and can hit target up to 150 kilometers high. However, this is still not fast or far enough to reliably hit ICBMs, according to most experts.
The farther a ballistic missile is designed to go, the higher and faster it must fly. This means that super long-range ICBMs travel at speeds around over twenty times the speed of sound and can fly up to thousands of kilometers above the Earth’s surface, making them much more difficult to intercept than shorter-range ballistic missiles, even when diving back to the surface in the terminal phase. To have a good shot at an incoming missile, interceptors of comparable speed are preferred.
This does not mean interception by slower missiles is strictly impossible. THAAD is claimed to have a limited capability for low-altitude ICBM interception. That is to say, it can try, but the odds of success would likely not be high.
Another issue is that THAAD has an effective range of around 124 miles—and possibly less versus an ICBM threat. While that suffices for defending a geographically confined area like the Korean Peninsula, across the sprawl of North America, two THAAD sites would mean defending just two metropolitan areas. So, hypothetically, the Los Angeles and San Francisco areas might receive the extra protection—while, say, Phoenix, Seattle and Portland could be out of luck.
At any rate, the latest Hwasong-15 rocket demonstrated sufficient range to fly across the continental United States, so a missile attack could simply be targeted at cities without THAAD. While this might have the benefit of making the closest, most densely populated cities less attractive targets, it would not help that much in protecting the nation as a whole unless batteries were deployed around all major cities. And that’s only assuming THAAD provides a useful ICBM defense in the first place.
Lockheed has proposed creating a THAAD-ER system, with an improved seeker and a two-stage rocket, giving the interceptors three times the range; supposedly, it could be operationalized in four years. While THAAD might conceivably have its ICBM-intercept capabilities improved, THAAD-ER and other upgrades exist only as design concepts for now.
The Submarine Threat?
One potential argument for West Coast THAAD batteries would be to defend against a potential North Korean submarine-launched ballistic-missile (SLBM) attacks. In August 2016, after numerous failed attempts, North Korea made its first successful test launch of an SLBM, the Pukkuksong-1, from a specially-designed Sinpo-class submarine.
The Pukkuksong-1’s exact capabilities are unclear, but at best it only qualifies as a medium-range ballistic missile—a type that THAAD is designed to engage. Furthermore, an SLBM launched closer to the U.S. coastline might give defenses less time to execute a midcourse interception, making a terminal interceptor a desirable backup.
However, the Sinpo-class submarine is an old-fashioned diesel submarine that would struggle to cross the Pacific, given its estimated operational range of only 1,500 miles and limited underwater endurance and acoustic stealth. The current version is unlikely to be able to enter within attack range of the U.S. mainland, though it could pose a threat to Pacific bases like Guam.
Of course, Pyongyang is undoubtedly working to improve the range of the submarine and its missiles. A new, larger Sinpo-C submarine was photographed under construction late in 2017, and an improved Pukkuksong-3 SLBM is believed to be in development.