After the September 11, 2001 terrorist attacks on the United States, elements of every Air National Guard unit in California has been activated in support of the Global War on Terrorism. Flight crews, aircraft maintenance personnel, communications technicians, air controllers and air security personnel were engaged in Operation Noble Eagle air defense overflights of major United States cities. In December 2007, after the grounding of F-15 fighters due to potential structural problems, the California Air National Guard assumed responsibility for defense of the western United States. This was the first time that a single state's fighter wing took responsibility of defense for an entire coast.