On September 15, 2001, POTUS George W. Bush authorized the mobilization of up to one million National Guard members for homeland defense following the attacks of September 11. This reservist operation is called Operation Noble Eagle. It did not require a mobilization of the scope that Bush authorized: it currently involves only 13,000 Air Force, 10,000 Army, 7,500 Marine, 3,000 Navy, and 2,000 Coast Guard reservists.

The main component of Noble Eagle is combat air patrol missions carried out over urban areas. Twenty-six air force bases have one hundred F-15 Eagle and F-16 Falcon fighter jets ready to scramble within ten minutes of a homeland security alert. There are also seven AWACS platforms in the air on loan from NATO, and several reserve KC-135 tanker aircraft for midair refueling. During the first three months of the operation, more than 200 CAP missions were diverted in pursuit of suspicious aircraft.

Though it is primary an aerial operation, Noble Eagle also involves military police, search and rescue personnel, and engineers from all services.

Sources:
http://www.globalsecurity.org/military/ops/noble-eagle.htm
http://www.af.mil/news/efreedom/index.shtml

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