Pursuant to a congressional request, GAO evaluated the: (1) Department of Defense's (DOD) efforts to consolidate management and funding of the North American Aerospace Defense Command's (NORAD) Integrated Tactical Warning and Attack Assessment (TW/AA) system modernization programs; (2) Air Force's progress in correcting five critical program deficiencies; and (3) Air Force's implementation of recommendations to conduct a cost-benefit analysis to determine the most effective and efficient means of meeting future communications processing needs at Cheyenne Mountain, which houses the TW/AA system. GAO found that the Air Force: (1) in compliance with a congressional mandate, consolidated five TW/AA modernization programs and requested $117.6 million for continuing the programs during fiscal year (FY) 1990; (2) expected to spend an additional $617 million through FY 1994 to complete the modernization effort; (3) identified 29 unresolved critical deficiencies in the 5 modernization programs; (4) began work to resolve critical Communications System Segment (CSS) Replacement Program problems involving uniform wiring standards, cabling congestion, and standardized message formats, but had not addressed other critical problems involving standard communication protocols or inconsistent message loading assumptions, although it recognized that the effectiveness of its other modernization programs relied on CSS effectiveness; (5) accepted CSS replacement hardware without resolving 12 unmet system specifications, and did not plan to formally test the hardware until July 1990; and (6) continued interim CSS upgrades, but did not perform a recommended cost-benefit analysis to determine the most efficient and effective means for satisfying communications processing requirements.