On 20 March, Thieu reversed himself and ordered Huế, Vietnam's third-largest city, be held at all costs, and then changed his policy several times. As the North Vietnamese launched their attack, panic set in, and ARVN resistance withered.
On 7 April, three North Vietnamese divisions attacked Xuân Lộc, 40 miles (64 km) east of Saigon. For two bloody weeks, severe fighting raged as the ARVN defenders made a last stand to try to block the North Vietnamese advance.
On 21 April, however, the exhausted garrison was ordered to withdraw towards Saigon. An embittered and tearful president Thieu resigned on the same day, declaring that the United States had betrayed South Vietnam. In a scathing attack, he suggested U.S. Secretary of State Henry Kissinger had tricked him into signing the Paris peace agreement two years earlier, promising military aid that failed to materialize.
On 27 April, 100,000 North Vietnamese troops encircled Saigon. The city was defended by about 30,000 ARVN troops. To hasten a collapse and foment panic, the NVA shelled the airport and forced its closure. With the air exit closed, large numbers of civilians found that they had no way out.
Schlesinger announced early in the morning of 29 April 1975 the evacuation from Saigon by helicopter of the last U.S. diplomatic, military, and civilian personnel. Frequent Wind was arguably the largest helicopter evacuation in history.
On 30 April 1975, NVA troops entered the city of Saigon and quickly overcame all resistance, capturing key buildings and installations. A tank from the 324th Division crashed through the gates of the Independence Palace at 11:30 am local time and the Viet Cong flag was raised above it. President Dương Văn Minh, who had succeeded Huong two days earlier, surrendered to Colonel Bùi Tín.
In the early morning hours of 30 April, the last U.S. Marines evacuated the embassy by helicopter, as civilians swamped the perimeter and poured into the grounds. Many of them had been employed by the Americans and were left to their fate.