Pursuant to a congressional request, GAO provided information on the Department of Defense's (DOD) Theater High Altitude Area Defense (THAAD) System, focusing on the: (1) expected cost, schedule, and acquisition quantities of THAAD; (2) expected role of THAAD within a National Missile Defense system; (3) relationship of range to peak reentry velocity for enemy ballistic missiles; and (4) ranges and types of ballistic missiles of developing countries. GAO found that: (1) the estimated cost for THADD could total $14.5 billion; (2) DOD plans to procure 1,422 THAAD missiles, 99 launchers, and 18 radars; (3) the THAAD program is scheduled to begin engineering and manufacturing development in 1996 and low-rate initial production in 1999; (4) THAAD is intended to defend against medium- to long-range theater ballistic missiles and will contribute to the national theater missile defense system; (5) the peak reentry velocity of enemy missiles is directly proportional to their maximum range and increases as their range increases; (6) there are more than 30 types of theater ballistic missiles in operation or under development in developing countries; and (7) the number of countries that possess long-range theater missiles is expected to increase.