Patriot air and missile defense systems demonstrated their effectiveness during Operation Iraqi Freedom by intercepting every Iraqi missile launched at Kuwait or Coalition forces, except those not engaged because Patriot computers calculated they would fall harmlessly into empty desert or into the open ocean. However, some intercepts took place at such short ranges and low altitudes that debris showered down on the targets. By contrast, the soon-to-be-fielded Theater High-Altitude Area Defense (THAAD) system intercepts short- and medium-range ballistic missiles at far greater ranges and much higher altitudes than the Patriot missile, an important consideration since missiles may be armed with chemical, biological or nuclear warheads.

The THAAD missile uses "hit-to-kill" technology to score direct hits on missile warheads just inside or just above the atmosphere, completely obliterating the warheads and negating fallout damage. The system consists of Launchers, Missiles, Battle Management/Command, Control, Communications and Intelligence units and THAAD radars. These elements work in concert to detect, identify, assign and destroy incoming theater ballistic missiles. In future theaters of operations, THAAD will serve as the upper tier while Patriot serves as the lower tier of a layered missile defense system. Together, they will protect U.S. and allied armed forces, broadly dispersed assets, and population centers against missile attacks.

Having proven its "hit-to-kill" capability in a series of flight tests, the THAAD system is currently in the engineering and manufacturing design, or EMD, stage of development. A robust ground-testing program is scheduled to precede flight testing, currently planned for fiscal year 2004; however, the Missile Defense Agency, which coordinates and manages the nation's Ballistic Missile Defense programs, is advocating an accelerated development program that would field an initial THAAD capability by the end of 2004.