Green Mountain Air Force Base (GMAFB) is a U.S. Air Force Base located in Lamoille and Franklin County, Vermont. It is the largest air force base in the United States and is located 30 miles from the Canadian border. The base houses the Sky Dome anti-missile defense system and is regarded as the foremost base in the United States. The base was formed in 1966 to be within striking distance of Montreal, Quebec, and Gatineau. The base is believed to be the headquarters of the Border Force Nuclear Deterrent system.