On September 11, 2001, the North American Aerospace Defense Command, based at Peterson Air Force Base, Colorado, under the command of Gen. Ralph E. Eberhart, oversaw three air defense regions, which were responsible for protecting the airspace over Alaska, Canada, and the continental United States. The last of these, the Continental United States NORAD Region (CONR), under the command of the dual-hatted commander of First Air Force, Maj. Gen. Larry K. Arnold, oversaw the Northeast, the Western, and the Southeast Air Defense Sectors. The locations of the departures, flight paths, and crash sites of the four aircraft hijacked on September 11, 2001, were all in the Northeast Air Defense Sector, commanded by Col. Robert K. Marr (see Diagram, NORAD Air DefenseStructure on 9/11, p 53).On September 11, 2001, the responsibility for defending continental U.S. airspace rested with only fourteen fighter aircraft at seven air defense alert sites across the country. Based in Rome, New York, the Northeast Air Defense Sector had only two alert sites on which to call-Otis Air National Guard Base in Cape Cod, Massachusetts, and Langley Air Force Base in Hampton, Virginia.Each site had two designated alert fighters on duty twenty-four hours a day, seven days a week. Many other fighter aircraft were based across the country, but they were not NORAD assets, and it would take time to arm them and organize their crews.