In light of recent developments involving North Korea, including its threat this week to attack Andersen Air Force Base in Guam, questions have been raised about how well the U.S. territory was defended against a ballistic missile attack.     Some in Guam have interpreted the statements made by Undersecretary  of Defense James Miller and Vice Chairman of the Joint Chiefs of Staff Admiral James Winnefeld at a March 15 press conference that the current U.S. Ground Based Midcourse (GND) system covers “all the United States” and “the entire United States” as indicating that the system covers Guam. The response by Undersecretary Miller is particularly significant as he was specifically asked about “American possessions in Western Pacific — Samoa, Guam, those areas.”  On Monday, Guam’s (non-voting) delegate to the U.S. House of Representatives, Madeleine Z. Bordallo, explicitly stated in a letter that this was the case:  “Additionally, I am aware that DoD officials are confident that the Ground-Based Midcourse Defense System will provide protection not only for the continental United States, but for Guam as well.

In fact, it is clear that this is not the case.  The figure below, from the 2010 Ballistic Missile Defense Review, shows the coverage of the GMD system against an ICBM from North Korea (I have added the arrow indicating Guam’s location).

Coverage of the U.S. Ground Based Midcourse Defense (GMD) against a North Korean ICBM.  The red arrow indicates Guam’s location. (Map from the Ballistic Missile Defense Review, p.15.)

As this figure shows, Guam lies more than 1,000 km beyond the perimeter that the GMD system is capable of covering.  This is hardly surprising as Guam is less than 3,500 km from North Korea, but about 7,500 km from the GMD interceptors in Alaska (the interceptors in California are even further away).

A seemingly more accurate description of the ability of U.S. missile defenses to cover Guam is this week’s response to a question from the Pacific News Center by the U.S. Joint Region Marianas:

“The Department of Defense fully intends to defend the United States and its territories from any ballistic missile attack.  The United States maintains a range of ballistic missile defense capabilities that could be deployed in Guam’s defense in times of crisis.”

That is, Guam is not defended against ballistic missile on a routine basis, but in “times of crisis” Patriot, Terminal High-Altitude Area Defense (THAAD), or Aegis SM-3 missile defense systems could be forward-deployed to Guam or its vicinity.  This approach apparently assumes at least some advance notice of a potential attack.  However, Representative Bordallo’s letter also stated that “I look forward to a more permanent Aegis missile defense capability in the future.”  Guam has been cited as a possible future site for an Aegis Ashore ballistic missile defense system (such as those planned for Romania and Poland) by the system’s manufacturer (Lockheed Martin).  Back in 2009-10, plans to deploy both a THAAD and a Patriot battery to Guam were being discussed, but this never happened.