	Introduction

The U.S. effort to develop and deploy ballistic missile defenses (BMD) based on the concept of hit-to-kill or kinetic energy kill began three decades ago. This effort gained momentum as the primary focus of the U.S. BMD program in the mid-1980s with the announcement of President Reagan's Strategic Defense Initiative (SDI). These test results and some very limited operational experience in wartime provide sufficient data for at least some conclusions regarding the decades-long U.S. investment in hit-to-kill as a concept for BMD. This overview report examines the U.S. investment in that concept, what that investment has produced, and raises various questions that might be considered. Therefore, this report will review and distinguish between the program results of theater missile defense (TMD) and national missile defense (NMD). Summary of Analysis

Analysis of flight test data shows that the U.S. effort to develop, test, and deploy effective BMD systems based on this concept has produced mixed and ambiguous results. Nor is there conclusive evidence of a learning curve, such as increased success over time relative to the first tests of the concept 20 years ago. Critics of the flight test effort to date, whether they support missile defense or not in general, can raise questions about the success rate and the realism of the testing effort, given a generation of U.S. investment in its development. Can kinetic energy interceptor technologies for use against long-range ballistic missiles be developed successfully and deployed as an effective part of the U.S. military posture? The answer appears to be ambiguous at this juncture. Still other observers could argue that in general the United States needs to make a more concerted effort to increase developmental testing across the board, before these systems are ready for more realistic testing regimes. They could argue that almost all the testing to date is of a developmental nature and that an operational testing regimen has not been developed, but remains essential.
For some time, U.S. ballistic missile defense (BMD) programs have focused primarily on developing kinetic energy interceptors to destroy attacking ballistic missiles. These efforts have evolved over 30 years and have produced a significant amount of test data from which much can be learned. This report provides a broad overview of the U.S. investment in this approach to BMD.
The data on the U.S. flight test effort to develop a national missile defense (NMD) system remains mixed and ambiguous. There is no recognizable pattern to explain this record nor is there conclusive evidence of a learning curve over more than two decades of developmental testing. In addition, the test scenarios are considered by some not to be operational tests and could be more realistic in nature; they see these tests as more of a laboratory or developmental effort. Success and failure rates (and their technical causes) have shown relative consistency through this period.
The U.S. flight test effort to develop theater missile defense (TMD) systems appears more promising. In relative terms, developmental and operational testing of TMD systems has been more successful than the NMD effort. Nonetheless, TMD systems that evolved from mature, existing ground and sea-based air-defense systems have demonstrated greater test success than other TMD programs.
How effective has the U.S. investment been in developing kinetic energy BMD systems? Observers could make any number of arguments as to what the record means and what could be done to improve the effectiveness of systems under development and of those deployed. Some observers have suggested that the 110th Congress might review the U.S. investment in the kinetic energy concept to date to determine how best to proceed with the U.S. BMD effort in the coming years. This report will be updated as events warrant.