According to U.S. intelligence, the threat to U.S airspace remains. The North American Aerospace Defense Command (NORAD) is to defend U.S. air space and the U.S. Air Force has 18 sites in the United States that conduct air sovereignty alert (ASA) operations. ASA operations support fighter aircraft in conducting homeland air defense operations. GAO examined the extent to which (1) NORAD has adopted a risk-based management approach to determine ASA operational requirements; (2) the Air Force has implemented ASA operations as a steady-state mission in accordance with Department of Defense (DOD), NORAD, and Air Force directives and guidance; (3) the Air Force assesses the readiness of units conducting ASA operations; and (4) the Air Force faces challenges in sustaining ASA operations for the future and what plans, if any, it has to address such challenges. GAO reviewed relevant ASA guidance, directives, and planning documents; and interviewed DOD officials, including the commanders of all 18 ASA sites. GAO recommends that DOD conduct routine risk assessments, implement ASA as a steady-state mission, and develop plans to address future challenges.