Summary: Pursuant to a congressional request, GAO reviewed the Department of Defense's (DOD) study on weapon systems procurement, focusing on the accuracy of the data and methodologies used in the study. GAO found that: (1) because DOD is generally optimistic in its weapon system procurement planning, DOD procurement programs are vulnerable to instability and unit costs could be higher than originally planned; (2) from 1992 to 1995, DOD incurred $240,000 in contractor support service costs for development, maintenance, and operation of the computer databases that support the study; (3) there were no material differences between the data in the study's database and the DOD Future Years Defense Program (FYDP) database; (4) there were no material problems with the methodologies used in the study; (5) the study could be more accurate if it used DOD historical procurement annex data to capture actual budgets for items; (6) the data is taken directly from DOD (FYDP) and the methodologies used to calculate average unit costs displays and other mathematical formulas is consistent with various DOD departments; (7) the study has been subjected to the same quality controls and supervisory reviews as other DOD studies; and (8) the most important point regarding the study is how well DOD responds to the relevant issues raised.