Update: WhiteFleet.net has a more thorough and up-to-date article addressing this topic: Ballistic Missile Defense: a Shield Against North Korea
Recently, there has been a bit of ado regarding the possible deployment of US THAAD ballistic missile interceptors in South Korea (which has declined to purchase the system for itself). THAAD, which stands for Terminal High-Altitude Area Defense, is an anti-ballistic missile system designed to obliterate ballistic missiles in the terminal phase of their flight (when they are descending towards their target). It intercepts ballistic missiles by hitting them with a missile of its own, head on. With a range of over 200km, one THAAD battery could cover a large portion of South Korea. THAAD is a high performance system, capable of reliably intercepting larger and more powerful missiles than other systems such as the Patriot or Cheongung II that South Korea currently fields.
On the surface, then, a THAAD deployment seems like a good idea. However, there are a number of reasons why the US deployment of THAAD is not as desirable for South Korea as it may seem. One important factor is that the prospect of THAAD in South Korea has raised alarm bells in China. China is weary of such a deployment, partially because of the AN/TPY-2 radar used by THAAD. The radar has a detection range of around 900km. Assuming the radar would be placed near the middle of South Korea and would look towards North Korea, the 900km range would allow the AN/TPY-2 to monitor a surprisingly large amount of activity over the airspace of North Korea and China, including missile launches. China also opposes the deployment on principle, and wants to limit US military involvement in the region.
It is important to note is that THAAD cannot shoot down ballistic missiles as they climb or in mid-flight. It is a terminal interceptor; it intercepts missiles as they descend towards their targets. Chinese objections to the interceptor’s deployment are somewhat hollow then, considering missiles bound for anywhere other than South Korea could not be intercepted by THAAD. The only operational system designed to shoot down ballistic missiles mid-flight is the US Ground-based Midcourse Defense system, or GMD, which has a far-from-perfect record and is not designed to stop a Chinese or Russian attack. However, with China’s trade with South Korea surpassing that of the US, China’s concerns are noted by Seoul regardless of their validity.
Factors other than Chinese objection cast doubt on the merits of a South Korean THAAD deployment. In order to understand the impact and utility of THAAD , it is important to consider THAAD’s capabilities and limitations. Each battery includes six launcher units; each launcher unit consists of a HEMTT truck with 10 missile canisters. So, a whole THAAD battery has 60 interceptor missiles total.
North Korea has “at least 400 Scud short-range tactical ballistic missiles, 300 No-Dong medium-range missiles, and 100 to 200 Musudan intermediate-range ballistic missiles.” Sixty interceptors (one US battery) against nearly 1,000 missiles from the North is quite an over-match. It is unlikely that each interceptor will hit and destroy one ballistic missile. While the system is nine for nine in testing, these tests cannot replicate the realities of real-world operations. Thus, even with a full US THAAD battery, the South Koreans would still have to rely on their Cheoungung II and Patriot missiles for the bulk of the intercepts, and even then many missiles will probably reach their targets.
It could be argued that multiple batteries could remedy this problem. However, with Seoul refusing to pay for THAAD, the most South Korea is likely to receive is a complimentary battery or two from the US, which would not be enough to prevent a massed attack. Even if the US was willing to pay for multiple THAAD batteries, the Chinese would all but certainly have spirited objections.
Also worth noting is that THAAD is on the wrong side of the cost curve by a large margin. Each THAAD interceptor missile reportedly costs around $10 million. North Korea sold one SCUD C theater ballistic missile (the kind of missile THAAD would defend South Korea against) for $3 million. The real production cost of each SCUD C is probably a good deal lower than $3 million, as the $3 million figure includes the profits North Korea obtained from the sale. Even without factoring the hundreds of millions worth of advanced TELs, fire control systems, battle management systems, and radars a THAAD battery requires, it already costs over twice as much to intercept a SCUD with THAAD as it does to launch the SCUD. Clearly, North Korea would be far ahead of the cost curve if a possible THAAD induced arms race were to break out; not to mention Pyongyang already has hundreds of ballistic missiles in its inventory.
What does this mean? For one, THAAD cannot and will not be the solution to the North Korean nuclear program or to North Korean missile proliferation. Seoul does not even want to buy THAAD, and the amount of missiles possessed by North Korea that can strike the South is simply too large. Plus, North Korea’s missiles are cheap. If an arms race were to break out, the North would be ahead of the cost curve. With China being South Korea’s largest trading partner, a theoretical US THAAD buildup (which China would surely protest loudly) is essentially out of the question.
Instead, the bulk of the ballistic missile interceptions in a wartime scenario will have to be performed by other systems, including the South’s indigenous Cheongung II system. Seoul may field an indigenous system similar to THAAD at some time in the distant future, but it would likely suffer from some of the same cost-related issues as THAAD, not to mention the difficulties of developing such a system in the first place. In all likelihood, the Korean peninsula will continue in its current state of limbo for quite some time, with the North making morbid threats on a semi-constant basis; the South will main its conventional superiority over the North as deterrent. After all, the South has kept the North at bay for decades without missile defense.