The Ground-based Midcourse Defense (GMD) system is currently the only U.S. missile defense system devoted to defending the U.S. homeland from long-range ballistic missile attacks. GMD and its associated elements span 15 time zones, including Ground-based Interceptors (GBIs) at two locations (Ft. Greely, Alaska and Vandenberg AFB, CA), seven types of sensors on land, sea, and space, and multiple and distributed fire control systems. By the end of 2017, there will be 44 deployed GBIs, 40 based at Ft. Greely, and four at Vandenberg AFB. The 2015 National Defense Authorization Act (NDAA) included funds to conduct environmental reviews of potential East Coast sites for a future addition to the GMD system.

When ballistic missile defense sensors detect a missile launch, these data are fused and fed into the GMD fire control system, which is used to launch one or more GBIs. The GBI will fly into the path of an incoming missile before releasing an Exoatmospheric Kill Vehicle (EKV), which uses onboard sensors to hunt down and physically collide with the warhead, destroying it on impact.

GMD is designed specifically to counter long-range ballistic missiles threatening the U.S. homeland. It uses a three-stage booster, giving the necessary “legs” to perform intercepts over great distances. This range gives GMD by far the greatest coverage area of any U.S. missile defense system, defending all fifty states and Canada. Other missile defense systems, including Aegis, THAAD, and Patriot, are generally classified as “regional” systems, and are geared toward short to intermediate range ballistic missile threats.  While some may have homeland defense applications in certain circumstances, they have much smaller coverage areas as compared to GMD, and generally much less capability, if any, against ICBMs.

Conversely, GMD is not capable of shorter range, regional defense missions. North Korea’s short and medium range missiles threatening South Korea and Japan, for example, fall outside of GMD’s engagement envelope. These threats require other solutions, such as Aegis, THAAD, or Patriot.

The GMD architecture emerged from the development of the Clinton Administration’s National Missile Defense (NMD) program. The Ballistic Missile Defense Organization (BMDO) formed the initial Joint Program Office for the NMD program in April 1997, with the goal of conducting an integrated test in 1999 and operational deployment by 2003.1 Flight testing of Ground-based interceptors began in 1997, with the first successful intercept in 1999.

Findings from the 1998 Rumsfeld Commission report asserted that the United States had underestimated the ballistic missile threat. This reassessment provided impetus for Congress to pass the 1999 National Missile Defense Act, which committed the United States “to deploy as soon as is technologically possible an effective National Missile Defense system capable of defending the territory of the United States against limited ballistic missile attack.”2

The Clinton administration ultimately deferred the decision to deploy homeland missile defense to the next administration.

In December 2001, the George W. Bush Administration announced that it would withdraw the United States from the 1972 Anti-Ballistic Missile Treaty, which opened the door to accelerated investment in a homeland missile defense system. In 2002, the White House issued National Security Presidential Directive 23 (NSPD-23), ordering the deployment of an initial limited homeland defense capability by 2004. In 2002, then-Secretary of State Donald Rumsfeld redesignated the BMDO as the Missile Defense Agency (MDA).3 In 2004, Lt. Gen. Henry “Trey” Obering, III, USAF, the Director of MDA, declared limited defensive operations including five GBIs in silos at Fort Greely, Alaska; an upgraded Cobra Dane Radar at Eareckson Air Station in Shemya, Alaska; and an upgraded radar at Fylingdales in the United Kingdom. The GMD system was intended to grow to 44 GBIs distributed between Fort Greely and Vandenberg Air Force Base.4 In addition, the Bush Administration proposed a European GMD site to counter the future development of an Iranian ICBM. This component of the GMD system would have included an additional ten GBIs in Poland and an X-band radar in the Czech Republic.5

In 2009, the Obama Administration announced the cancellation the European GMD sites proposed by the Bush Administration in favor of the European Phased Adaptive Approach.6 The administration also capped the planned GBI deployments to 30, a reduction from the 44 planned under Bush.7 In 2013, then-Defense Secretary Chuck Hagel announced a reversal of the decision to reduce the U.S. based interceptors and reconstituted a plan to deploy 44 GBIs by 2017.8 In 2015, the administration also awarded a contract to build the S-band Long Range Discrimination Radar (LRDR) at Clear Air Force Station in Alaska to improve the discrimination capability of the radars in the system.9 The FY 2016 NDAA authorized $1.8 billion in funding for the GMD system to improve the CE-II kill vehicle, develop a Redesigned Kill Vehicle (RKV), invest in the LRDR, and support advancements in a selectable two or three stage GBI booster.10