U.S. homeland against nuclear attacks, attacks involving other weapons of mass destruction (WMD), or conventional ballistic missile attacks; (2) protection of U.S. forces, including military bases, in theaters of operation against ballistic missile attacks armed with WMD or conventional munitions; and (3) protection of U.S. allies, partners, and host nations against ballistic-missile-delivered WMD and conventional weapons.8 A fourth mission, protection of the U.S. homeland, allies, and partners against accidental or unauthorized launch, was considered as a collateral benefit of any ballistic mission defense but not as a goal that drives system requirements.9 Consistent with U.S. policy and the congressional tasking, the committee conducted its analysis on the basis that it is not a mission of U.S. BMD systems to defend against large-scale, deliberate nuclear attacks by Russia or China.10

BMD intercept can, in principle, be accomplished in any of the three phases of flight of the target missile: boost phase, midcourse phase (which can in turn be subdivided into early, ascent, and postapogee or decent phases), and terminal phase. Further elaboration of this terminology is provided in Box 1-1.

Figure 1-2 displays the present and proposed U.S. BMD systems for countering SRBM, MRBM, IRBM, and ICBM threats in the context of their phases of flight. In addressing the congressional tasking, the committee examined a wide range of present and proposed BMD systems, along with their supporting sensors. The BMD systems examined in this report are shown in Table 1-1, where they are displayed in terms of their applicability to a given protected area and mission (i.e., protecting the U.S. homeland, allies, or U.S. forces) and to a given layer of defense (terminal-, midcourse-, or boost-phase defense). The programs of record for the particular defense systems are described in Chapters 2 and 3. In addition, the committee examined two other defense systems—CONUS-based evolved GMD (denoted as GMD-E in Chapter 5) and Forward-Based Evolved GMD—that resulted from its analysis and simulation work, where it found significant weaknesses in the current systems.

While the committee had access to classified information provided by the Missile Defense Agency on its programs of record, the committee chose to


8For brevity, missions (2) and (3) are usually considered together because they so often involve defense against hostile missiles of similar character although being defended against for different purposes.

9Any BMD system would provide some inherent capabilities for defense against accidental or unauthorized launch of a Russian or Chinese missile or, for that matter, one owned by another power. However, defense against such attacks should not drive the design or evaluation of defense concepts, because the greater sophistication (or numbers) of such an attack would tend to establish unrealistic and perhaps infeasible or unaffordable requirements compared to those appropriate for defenses focused on the rogue state threat.

10Aside from political and stability effects, such defense is not practical, given the size, sophistication, and capabilities of Russian and Chinese forces and both countries’ potential to respond to U.S. defense efforts, including by increasing the size of the attack to the point at which defenses are simply overwhelmed by numbers.

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