The U.S. escalation of ground activity in South Vietnam and aerial bombardment of North Vietnam that began in 1965 produced massive casualties, a stalemate on the battlefield and destruction of the northern economy. This caused a sharpening of differences within the North Vietnamese government over how to continue prosecution of the war.
Relative moderates called for a return to protracted guerrilla warfare while negotiating with the United States, in a coordinated effort to erode U.S. public resolve. The militant faction tended to follow the People's Republic of China in matters of foreign relations, rejecting negotiations with the U.S., although their military strategy centered on large-scale, main force actions rather than protracted guerrilla warfare. A July 1967 purge of the moderates set the stage for a move to ignite a revolution in South Vietnam by means of a major, conventional offensive.
General Offensive, General Uprising
The North Vietnamese dubbed this initiative General Offensive, General Uprising, but in the United States it would become known as the Tet Offensive. Hanoi believed that the government in Saigon and the U.S. presence in the South were so unpopular that coordinated, large-scale attacks would spark a popular uprising. That in turn would position the North Vietnamese and their Viet Cong comrades to sweep to a conclusive victory. At the same time, they recognized that confidence among the American public in the Johnson Administration was waning. If the Communists could not defeat the U.S. on the battlefield, they would defeat the U.S. by causing a loss at home of popular support for the war.
The Tet Offensive was planned in three stages. Phase I would begin in the fall of 1967 with a series of probing attacks that would test American defenses while drawing US forces out to the margins of South Vietnamese territory. In Phase II, weak points identified during the first phase would be struck while Viet Cong units launched attacks within South Vietnam’s cities. "Phase II" is now remembered as the Tet Offensive. The planners in Hanoi imagined that these initiatives would bring South Vietnam's masses to rally to the communist cause, while Army of the Republic of Vietnam (ARVN) units crumbled and the Saigon government collapsed under coordinated communist military pressure and propaganda. In Phase III, large-scale battles by conventional ground forces would compel demoralized U.S. military units to retreat to coastal enclaves.
Thanks to flawless execution of the first phase, the Communists were well aware of U.S. and ARVN force dispositions when the second phase began.
Miscalculation in the U.S. Joint Command
General William Westmoreland, commander of Military Assistance Command, Vietnam (MACV) was primarily concerned at the time with the situation at the Khe Sanh Combat Base. That U.S. Marine Corps outpost was located about 30 kilometers south of the demilitarized zone (DMZ) between the North and South Vietnamese nations. Ten days before the onset of the Tet Offensive, a force of around 30,000 North Vietnamese troops had besieged the U.S. Marine garrison at Khe Sanh and MACV was convinced that the assault was a prelude to an effort to seize the two northernmost provinces of South Vietnam. To prevent such a development, Westmoreland had deployed the bulk of an entire Marine division to South Vietnam's northernmost province, leaving the city of Hue relatively unguarded.
The Strategic Importance of Hue
Highway 1 was an important supply line for South Vietnamese and U.S. forces, running along the South China Sea coast from Da Nang up to Hue, then continuing on for about 80 kilometers to the northwest before reaching the DMZ. Considering its logistical importance and its proximity to the border zone, Hue should have been well-prepared for an attack, but the city had been left poorly defended.
The Tet Offensive kicked off on January 30, 1968, with approximately 74,000 People's Army of Vietnam troops streaming across the border. Coordinated PAVN and Viet Cong attacks on Hue began in the early morning hours of January 31. Despite the one-day notice, this major city was largely unprepared for the onslaught.