High Quality Content by WIKIPEDIA articles! Operation Niagara was a U.S. Seventh Air Force close air support campaign carried out from January through March 1968, during the Vietnam War. Its purpose was to serve as an aerial umbrella for the defense of the U.S. Marine Corps Combat Base on the Khe Sanh Plateau, in western Quang Tri Province of the Republic of Vietnam. The base was under siege by an estimated three-divisional force of the People`s Army of Vietnam (PAVN).