For FY2006, the Bush Administration requested $8.73 billion for the Missile DefenseAgency (MDA) budget. This includes $3.3 billion for the Ground-Based Interceptor (GBI) program,currently being deployed in Alaska and California. The House-passed defense authorization bill( H.R. 1815 ) provides $8.83 billion, an increase of $100 million for the ground-basedmissile interceptor program. The Senate-passed authorization bill approved $8.73 billion for MDA( S. 1042 ) and similarly specified that $100 million of the funds provided for theMidcourse Defense Segment be used to enhance the ground-based missile interceptor test program.The House-passed defense appropriations bill ( H.R. 2863 ) includes $8.58 billion forMDA. It too specifies an additional $100 million for ground-based missile defense interceptortesting. The Senate-passed appropriations bill provides $200 million more for the ground-basedmissile defense interceptor program and $65 million for the Israeli Arrow system. Although missile defense remains strongly supported, Congress and others have raisedquestions and concerns over several programs, including the Airborne Laser, the SSTS (SpaceSurveillance and Tracking System), and the BMD System Interceptor program. Some concerns alsoremain over significant flight test delays in the ground-based system being deployed in Alaska andCalifornia. Recent milestones reported by MDA include a successful intercept by the Navy's sea-basedmissile defense program, a successful flight test of the revamped Theater High Altitude AreaDefense (THAAD) system, a successful flight test of the ground-based mid-course defense (GMD)interceptor, and deployment of the 10th operational interceptor of the GMD system. [author name scrubbed] & Amy A. Woolf, Specialists in NationalDefense In July 2001, the Bush Administration presented to Congress the outlines of its proposedapproach to missile defense. The Bush Administration's plan differed significantly from theapproach pursued by the Clinton Administration. The issue for Congress remains whether toapprove or modify the Bush Administration's proposed approach for missile defenses. In general,Congress has supported the President's approach, making some adjustments in programsexperiencing technical problems and reducing funding for programs that Congress was not yetwilling to commit to for early deployment purposes. In December 2002, the Administration announced its decision to begin fielding initial missiledefense capabilities in 2004-2005. An initial national missile defense capability was declared withthe deployment of eight interceptors in Alaska and California at the end of 2004. This report provides background information on the Bush Administration's proposedapproach, and discusses key issues relating to it. Key issues raised in the next section include: Ballistic Missile Proliferation : Which countries of concern possess or aredeveloping missiles that might threaten the United States, its military forces, or its friends and allies?What range of missile threats might U.S. missile defenses be required to counter in the near andmid-term? Technology issues: Will the United States be able to develop and deploymissile defenses that can intercept missiles of all ranges and at all phases of their flights? If not, cana partial system be overcome even by rogue states? What are the key technological challenges? When might the research and development program give way to a deployment program? WillDOD's acquisition policy affect the planned incremental deployment strategy? The latter sections of the report provide background information on the various parts of theAdministration's proposed missile defense program. It includes program and budget data, and keytechnical challenges faced by the programs. The report concludes with a summary of congressionalaction on the missile defense budget. The United States has pursued the development of missile defenses for more than 50 years. Since the Reagan Strategic Defense Initiative (SDI) was launched in FY1985, the United States hasspent more than $85 billion on missile defense programs and studies. Missile defense has provento be a challenging and elusive endeavor. Moreover, the question of whether the United Statesshould deploy extensive defenses to protect against ballistic missile attack has been one of the mostdivisive political and national security issues of this generation. The demise of the Soviet Union and the debate over the emergence of ballistic missile threatsfrom other nations changed the nature of the debate. For many, concerns about nuclear stabilitybetween the United States and Russia have receded as the two nations expanded their areas ofcooperation and improved their relationship, especially in the U.S. lead war on terrorism. Instead,many now focus on concerns about a possible attack from an adversary who possesses only a fewmissiles and may not be deterred by fear of U.S. retaliation. Without a missile defense capability,some argue, the United States itself may be deterred from using its conventional forces to protectU.S. allies and friends. Similarly, the United States might be unable to combat aggressive orprovocative actions on the part of "rogue states" armed with chemical, biological, or nuclear capableballistic missiles. (1) Eventerrorist acquisition of ballistic missiles armed with weapons of mass destruction is today part of thepolicy debate. The Clinton Administration responded to this changing international security environmentby pursuing the development and deployment of defenses that would protect U.S. allies and forcesin the field from attack by shorter and medium-range ballistic missiles (theater missile defense:TMD). It also sought to develop for deployment a limited system to protect U.S. territory fromattack by longer-range ballistic missiles (national missile defense: NMD). Its plans for NMD wouldeventually have conflicted with the terms of the 1972 Anti-ballistic Missile (ABM) Treaty with theSoviet Union, which limited the United States and Soviet Union (now Russia) to a single, land-basedsystem for defense against long-range ballistic missiles. The Administration sought to preserve thebasic framework of the ABM Treaty by negotiating modifications that would have permitted thedeployment of a limited, land-based NMD site in Alaska. The Clinton Administration decided,however, that it would not proceed to deploy the site after failures in the flight test program and othertechnical concerns raised questions about the readiness of the technology. The Bush Administration sharply altered the debate over missile defense. In severalpre-election speeches, President Bush indicated that he would pursue the development oftechnologies that could be deployed on land, at sea, and in space to protect the United States, itsallies, and its forces overseas from ballistic missile attacks from rogue nations. President Bush alsostated that the United States would have to "move beyond the constraints" of the ABM Treaty. Heemphasized that "Russia is not our enemy," and, therefore, Russia should not be concerned aboutU.S. deployment of missile defenses. Instead of seeking to modify the ABM Treaty so that theUnited States could deploy limited missile defenses, the President said "we need a new frameworkthat allows us to build missile defenses to counter the different threats of today's world." (2) The Administration began to outline the details of its plans for missile defenses in July 2001,after submitting its amended defense budget for FY2002 to Congress. In that budget, theAdministration requested $8.3 billion for missile defense, an increase of $3.1 billion or 61 percentover the amount Congress funded for FY2001. The Administration stated that it would explore abroader range of technologies and basing modes, "including land, air, sea, and space-basedcapabilities that had been previously disregarded or inadequately explored." However, as isdescribed in more detail later in this report (see Table 1 ), the Administration appears to haveessentially increased funding evenly for each of the missile defense and sensor technologies alreadyin the defense budget. From a funding and programmatic perspective, the Administration did notappear to give increased priority to any particular program or introduce any major new researchdirections for FY2002 beyond what the Clinton Administration was already pursuing, except toaccelerate the process and integrate key components. A similar argument was made with respect tothe FY2003 missile defense budget of $7.8 billion. In its missile defense program, the Bush Administration eliminated distinctions betweentheater and national missile defenses (TMD and NMD). Instead, according to General Kadish, thedirector of MDA (formerly the Ballistic Missile Defense Organization (BMDO)), the Administrationhas "developed a research, development, and test program that focuses on missile defense as a singleintegrated BMD system." Furthermore, the objective of this program is to "aggressively evaluateand develop technologies for the integration of land, sea, air, or space-based platforms" and todevelop and deploy a global system of "layered defenses, capable of intercepting missiles of anyrange at every stage of flight -- boost, mid-course, and terminal." (3) Administration officials have highlighted two primary benefits of layered defenses. First,layered defenses would seek to provide the United States with more than one opportunity to targetan attacking missile, thus arguably increasing the chance of shooting it down. (A critique of thelayered defense concept is outlined in the section on Technology and Other Challenges.) Second, the layers could complicate an attacker's ability to defeat the overall system. Thisis because countermeasures, which are intended to confuse or overcome defenses, that might beeffective in one phase of a missile's flight might not work in other phases. The Bush Administration has emphasized that its missile defense program will concentrateon "robust research and development" into a wide range of missile defense technologies.