President Johnson referred to the Khe Sanh air campaign as “the most overwhelming, intelligent, and effective use of airpower in the history of warfare. "Operation Niagara" was the code name for the aerial onslaught that was unleashed on NVA troops that were amassing around the Marine base. The operational name was chosen by General Westmoreland to give the visual image of bombs cascading from the sky and the mission lived up to its moniker. B-52s flew 2,548 combat sorties and released 59,542 tons of bombs on North Vietnamese positions during "Operation Niagara".
The Khe Sanh combat base was located on Highway 9 just south of the Demilitarized zone. Its purpose was to impede the infiltration of NVA troops and supplies into South Vietnam. It contained an airfield and was the home to approximately 6,000 marines in January of 1968, when American intelligence determined that approximately 20,000 NVA troops had begun to surround the base; two divisions directly confronted Khe Sanh with a third in the immediate vicinity.
Combat Skyspot played a vital role in the bombing effort. This battle was the first large scale use of “close-in” bombing by B-52s and the beginning of “Bugle Note”
Defending Khe Sanh became a critical mission; the Joint Chiefs of Staff voted unanimously to acceptGeneral Westmoreland's plan to repel the attack. President Johnson was briefed regularly and the siegereceived national attention.
The besieged Marines relied on air power to provide the majority of defense and to airlift supplies while the enemy had successfully blocked ground routes.
According to one analysis of the air assault, the effectiveness of the aerial bombardment depended on three critical decisions made at the outset:
The first was to use the Boeing B-52 Stratofortress (BUFF) for area bombing in direct support of thedefenders. Each Stratofortress was loaded with either 108 500-pound general-purpose bombs, or a mixed load of 84 500-pound bombs and 24 750-pound bombs—a significant amount of firepower. The second critical decision was to implement the Combat Skyspot bombing system and the Marine AN/TPQ-10 radar for improved bombing accuracy. The third decision was to reduce the normal 3-kilometer bombing safety zone to 1 kilometer, which meant that the B-52 could be used in what amounted to a close-air-support role. 
Once the decision was made to use B-52's, the second decision centered on maximizing the BUFF's effectiveness using radar directed bombing and a new procedure called “Bugle Note”. The combat area was divided into a grid system of blocks that were 1 kilometer by 2 kilometers, the area a cell of 3B-52's could saturate with high explosives. Almost immediately, six B-52 cells became the standard.
Every 90 minutes on the average, a 3-plane cell would arrive at a chosen point where it would be picked up by a Combat Skyspot control unit and directed through a series of check points toits particular target block. … After only a day's "Bugle Note" operation, General Wells' headquarters proposed a major change, to provide six B-52's every three hours rather than three every 90 minutes. Adoption of this proposal would permit even more devastating target coverage. 
Targets could be changed up to two hours prior to target time. A constant stream of aircraft meant that the bombing could occur around the clock.
 Head, Dr. William P., PhD, "WAR FROM ABOVE THE CLOUDS, B-52 Operations during the Second Indochina War and the Effects of the Air War on Theory and Doctrine", Air University Press, Maxwell AFB, July 2002, pg. 32
 Bernard C. Nalty, "Air Power and the Fight for Khe Sanh", (Office of Air Force History, Washington, DC 1973) pg. 88
 Maj. Edward F. Matignetti, USAF, “To Bomb or Not to Bomb: Area Bombing in the Age of Precision Munitions” (Thesis, Air University, Maxwell AFB 2006 )
 Nalty, "The Fight for Khe Sanh", 82
 Head, "WAR FROM ABOVE THE CLOUDS", Air University Press, Maxwell AFB, July 2002, pg. 32