Aegis Ashore vs THAAD (July 27, 2015)

In a comment to my post of July 16 about the THAAD deployment in Guam being made permanent, a question was raised about why THAAD was proposed for South Korea and Aegis Ashore for Romania and Poland (and why not vice versa).

There are two main technical issues that almost certainly drove the decision of which system went where:

(1) Europe can be almost completely covered by two Aegis Ashore sites but achieving similar coverage with THAAD would require a prohibitive number of THAAD batteries.  On the other hand, S. Korea is small enough to be covered by one or two THAAD batteries.

A single Aegis Ashore site (with the Block IIA interceptor) can cover a much larger geographical area than a single THAAD deployment.  The Block IIA interceptor is scheduled to begin deployment in 2018.  This larger coverage area occurs because the Aegis Block II interceptor has a much higher burnout speed (likely about 4.5 km/s) than a THAAD interceptor (likely about 2.6-2.8 km/s) and thus can reach out to make intercepts at much greater ranges.

This is illustrated in two 2007 Missile Defense Agency Briefing slides.  The yellow “footprints” in Figure 1 below shows the area that could be covered by three THAAD batteries in eastern Turkey against Iranian ballistic missiles.  For THAAD, this situation — in which the attacking missiles are launched from a country bordering the country targeted – is closely analogous to the North Korea-South Korea situation.  However, the three THAAD batteries together cover only a small fraction of Turkey.


Figure 1.  Coverage of Europe against Iranian ballistic missile by THAAD, Aegis (Block IB), and two-stage GBI interceptors.  Slides from MDA Executive Director Patricia Sanders, “Missile Defense Program Overview For The 4th International Conference On Missile Defense,” June 26, 2007.  Available at:


THAAD Battery to be Permanently Deployed in Guam (July 16, 2015)

The U.S. Army has announced plans to make the deployment of a Terminal High-Altitude Area Defense (THAAD) missile defense system in Guam permanent. This would be the first permanent deployment of a THAAD battery outside the continental United States.  The Army has released a fact sheet and draft environmental assessment about the proposed permanent basing and has already held two public meetings in Guam about it.

The THAAD battery was first deployed to Guam on an “expeditionary” basis in April 2013, following North Korean threats to the Island.  The Google Earth image below shows the initial deployment of the THAAD battery’s TPY-2 radar and other equipment. (A THAAD battery consists of a TPY-2 X-band radar and associated equipment, a command and communications unit, and a number of truck-mounted launchers (typically as many as six) each of which can carry eight THAAD interceptors.)


The picture above, from February 2014, shows the original (“expeditionary”) deployment of the THAAD TPY-2 radar on Guam.  The radar equipment is at the top of the image, just left of center.  The antenna unit is the thinner object at the top.  Immediately behind it is the electronic equipment unit.  Perpendicular to and to the right of the electronic equipment unit is the cooling unit.  Perpendicular to and to the right of the cooling units are two electrical power units.  One or more of the three objects behind the power units may be additional THAAD equipment (truck-mounted missile launchers or the command and communications unit). Google Earth image, February 4, 2014.