Less than three weeks after Department of Defense officials incorrectly stated that Guam was covered by the U.S. Ground-Based Midcourse Defense (GMD) national missile system, the Department announced today that a Terminal High-Altitude Area Defense (THAAD) battery would be deployed to Guam. The U.S. currently has two deployable THAAD batteries with a third undergoing training, all at Fort Bliss, Texas, and currently plans to buy a total of six, although this number could increase. Each battery consists of a TPY-2 X-band radar, up to six launchers (although the current batteries only have three each), each of which can carry as many as eight interceptor missiles, and a fire control system.
This would be the first operational deployment of a THAAD battery away from Fort Bliss. In June 2009, in response to indications of North Korean plans to test a long-range missile, Defense Secretary Robert Gates stated that a THAAD battery had been deployed to Hawaii.[1] However, this was only a temporary activation of THAAD components that happened to be in Hawaii at that time for testing purposes.[2] As of late 2009, the U.S. Army planned to deploy both Patriot and THAAD batteries to Guam, but this never took place.
One interesting question that announcement raises is: Once the system is deployed in Guam, under what circumstances could it ever be removed?
[1] Viola Glenger and Tony Capaccio, “Gates Order Measures Against North Korea Missile (update2),” Bloomberg.com, June 18, 2009; Peter Foster, “N. Korea May Fire Missile At Hawaii, Report Says; U.S. Prepared: Gates,” National Post (Canada), June 19, 2009, p. A15.
[2] Amy Butler, “THAAD Turnaround,” Aviation Week and Space Technology, August 17, 2009, p. 38.
mostlymissiledefense 
Allen Thomson
/ April 3, 2013Another interesting thing to think about is the radar coverage the US is acquiring in that part of the world, remembering that a THAAD fire-control AN/TPY-2 is switchable to a FBX-T missile early warning radar on short notice.
Looking at coverage sectors, we see
AN/TPY-2 at Guam — ca 270 to 30 degrees
AN/TPY-2 in South Japan — ca 240 to 360 degrees
AN/TPY-2 in North Japan — 210 to 330 degrees
And, if Taiwan is going to share the Leshan Pave Paws data,
Pave Paws on Taiwan — 180 around to 270, 0 and on to 60 degrees
I wonder what the folks in China are making of this.