Page:A Concise History of the U.S. Air Force.djvu/76

 tion with one of assured survival, in the form of the Strategic Defense Initiative (SDI). SDI was to focus on the development and deployment of a combination of defensive systems such as space-based lasers, particle beams, railguns, and fast ground-launched missiles, among other weapons, to intercept Soviet ICBMs during their ascent through the Earth's outer atmosphere and their ballistic path in space. While the ABM Treaty restricted various methods of testing SDI weapon systems, the end of the Cold War and collapse of the Soviet Union removed the justification for the level of research and development associated with this project, although research continued at a much reduced level under the Ballistic Missile Defense Organization.