"The September 11th attacks drew attention to U.S. air defense, and the 9/11 Commission Report recommended that Congress regularly assess the ability of Northern Command to defend the United States against military threats. Protecting U.S. airspace may require improvements in detecting aircraft and cruise missiles, making quick operational decisions, and intercepting them. A number of options exist in each of these areas. A variety of issues must be weighed including expediency, cost, and minimizing conflicts with civilian aviation."
CRS Report for Congress, RS21394