The Strategic Defense Initiative concept envisioned a three-tiered defensive system - creating the ability to intercept a target missile in the boost, midcourse and terminal phases of its flight.
By 1984, with over 25-years of experience in ballistic missile defense, the Army and more specifically this command, then known as the U.S. Army Strategic Defense Command (USASDC), was given the lead in most of the SDI programs. In the boost phase, the system incorporated a Boost Surveillance and Tracking System, the Space Based Laser and the Ground Based Laser. The Army shared responsibility for the SBL with the Air Force, while it was assigned sole control over the GBL.
In the midcourse phase, the SDI system architecture envisioned a Space-Based Surveillance and Tracking System, a Space Based Interceptor (SBI), a Neutral Particle Beam, and the Exoatmospheric Reentry-vehicle Interceptor Subsystem (ERIS). The Air Force oversaw the development of the SSTS and the SBI and shared responsibility with USASDC for the NPB. The Army directed the development of the ERIS. The final layer of defense, the terminal phase, employed the Airborne Optical Adjunct, the Ground Based Radar, the Ground Based Surveillance and Tracking System (GSTS) and the High Endoatmospheric Defense Interceptor (HEDI). The USASDC was the lead on all of these programs. Finally, development of a Battle Management/Command, Control and Communications system was shared by all three primary elements: the Air Force, the Army and SDI Organization.