Yesterday the Missile Defense Agency (MDA) announced a successful test of the Terminal High Altitude Area Defense (THAAD) missile defense system against an intermediate‐​range ballistic missile (IRBM) target. This is a significant milestone for the THAAD system, which was recently deployed to South Korea to defend southern cities and the port of Busan against missile attack by North Korea. Even though this particular test was planned months ago, its timing is especially important given North Korea’s successful test of the Hwasong‐​12 IRBM in May 2017.

Despite the successful test, it would be dangerous and premature for U.S. policymakers to read too much into THAAD’s capabilities. Initial information about the test suggests that it did not reflect a wartime use of an IRBM by North Korea. Moreover, the test could have negative implications for U.S.-China strategic stability.

Based on the statement released by the MDA and video of the test, the test seems to have been relatively easy for THAAD. For example, at the moment the warhead is intercepted it does not seem close to any other objects. This makes it relatively easy for THAAD’s infrared sensor to locate the warhead and slam into it. However, it would be much harder for the sensor to locate the warhead if the target missile broke up in flight and cluttered the sensor. It is not clear whether the target missile used in the most recent test broke up in flight, but based on past tests it seems unlikely. This makes for successful testing, but it does not reflect real‐​world scenarios.

An additional departure from real‐​world conditions is the apparent lack of countermeasures on the target missile. Countermeasures such as decoy warheads or chaff make it harder for THAAD to find the warhead. These devices do not have to be incredibly advanced or expensive to be effective. It is safe to assume that North Korea has some rudimentary countermeasures on its missiles, and it will likely develop more sophisticated countermeasures in the near future. A recent test of the Ground‐​based Midcourse Defense system did feature countermeasures, but the MDA has not said if countermeasures were part of the recent THAAD test. So long as missile defense tests are relatively controlled and sanitized they cannot reveal much information about how the systems would perform in a combat scenario.

At the strategic level, this successful intercept test of an IRBM target will exacerbate Chinese concerns about THAAD. China’s opposition to THAAD deployment in South Korea and the effect of missile defense systems on U.S.-China strategic stability are well documented. Missile defense advocates insist that THAAD does not threaten China’s strategic nuclear deterrent because the system is meant to respond to shorter‐​range missiles that don’t threaten the American homeland. U.S. officials also insist that there is a difference between regional missile defense systems like THAAD and homeland missile defense systems.

THAAD’s ability to successfully engage IRBMs could blur the distinction between regional and homeland missile defense and bolster arguments by Chinese observers that such a distinction does not really exist. Is a missile defense system truly “regional” if it can defend U.S. territory like Guam, Alaska, or Hawaii from nuclear attack? This may be a bridge too far in terms of what THAAD is capable of doing from a technical perspective, but Chinese perceptions of missile defense effectiveness, correct or incorrect, will shape the development of their nuclear forces.