In the meantime, the situation in South Vietnam had deteriorated dramatically. On 8 January, the North Vietnamese Politburo, satisfied that the initial PAVN probing attacks had stretched the ARVN to the limit, ordered a major offensive. This broke first in the Central Highlands, where the PAVN 316th, 320th and A-10 PAVN Divisions struck at Ban Me Thout in the early morning hours of 10 March. The ARVN 53rd Regiment resisted gallantly, but, being heavily outnumbered and under constant artillery fire, was quickly driven back into an untenably small perimeter. Efforts by the 23rd Division, which controlled ARVN units in the area, to reinforce the position came to nothing and ARVN morale began to crack when the Division Commander took advantage of a slight wound to leave the town. By 18 March, the battle was over and communist units were driving the 23rd's two remaining infantry regiments from the last feasible blocking positions to the east.
At this point, President Thieu made a fateful decision: while the battle for Ban Me Thout was still in progress, he concluded that it was beyond the capabilities of his forces to defend the entire country, but that the southern half, containing the bulk of the population and natural resources, could be held. He therefore ordered the commander of II Corps, Major General Pham Van Phu, to evacuate Pleiku, the regional headquarters and principal ARVN base in the Central Highlands, as a precondition to recapturing Ban Me Thout to the south. PAVN elements had already blocked the main roads between Pleiku and the coast, so General Phu selected Route 7B, a narrow logging road that wound south to Tuy Hoa, for the evacuation. Several bridges on the long-disused road were down, and the relief operation would demand surprise, strong leadership and perfect timing. None of these conditions prevailed.
The first convoys left Pleiku on 16 March and continued to depart unhindered for three days. But no provisions had been made for the civilian populace, and the military convoys were pursued by a panic-stricken civilian mob in vehicles and on foot. Surprised at first, the PAVN reacted quickly and by 18 March portions of the evacuation route were under artillery fire. Worse, necessary bridging material was delayed. and a mass of vehicles and humanity backed up at each river crossing in turn. Panic mounted and observers overhead watched in horror as survivors plodded south suffering terrible heat and thirst. Communist forces finally cut the readjustshort of Tuy Hoa on 22 March. Desperate attacks by ARVN Rangers eventually reopened the way, and, during the evening of 27 March, the first vehicles began to roll into Tuy Hoa. Of those who started the trek, only a minority completed it. They included some 60,000 civilian refugees, perhaps a third of the total who started, and some 20,000 support troops, only a quarter of those who departed Pleiku. Of the elite Rangers who covered the withdrawal, only 900 out of 7,000 survived. During the ordeal, graphic footage of the "Convoy of Tears," as it was called, was screened on South Vietnamese television, and panic spread to the entire nation. Meanwhile, as the ARVN scrambled to salvage something from defeat, the situation in the north fell a part. By 19 March, Quang Tri Province had fallen to the communists. Successive attempts to evacuate the ARVN forces of the strategic reserve southward were inadequate and poorly planned and served only to amplify the chaos; Hue fell on 25 March and Da Nang on 30 March. The result was the loss not only of northern South Vietnam, but also of the elite units of the strategic reserve, the 1st Division and the Marine and Airborne Divisions. By 1 April, South Vietnamese forces had abandoned Qui Nhon, Tuy Hoa and Nha Trang and within the week PAVN was outside the gates of Saigon. There, with bitter irony, they were briefly halted at Xuan Loc by the ARVN 18th Division - never considered an elite unit- and the remnants of the 1st Airborne Brigade. Fighting without effective air support -for Soviet-supplied SA-7 shoulder-fired, heat-seeking missiles had neutralized the VNAF's fighter bombers - the 18th slugged it out with no less than three communist divisions for twelve long days before being surrounded and overwhelmed, giving better than they got and dispelling forever the myth of ARVN unwillingness to fight. It was a magnificent but futile effort. By 20 April, only shattered remains stood between the victorious PAVN and Saigon.