With the northern half of the country under their control, the Politburo ordered General Dung to launch the final offensive against Saigon. The operational plan for the Ho Chi Minh Campaign called for the capture of Saigon before 1 May. Hanoi wished to avoid the coming monsoon and prevent any redeployment of ARVN forces defending the capital. Northern forces, their morale boosted by their recent victories, rolled on, taking Nha Trang, Cam Ranh, and Da Lat.
On 7 April, three North Vietnamese divisions attacked Xuan Loc, 40 miles (64 km) east of Saigon. The North Vietnamese met fierce resistance at Xuan Loc from the ARVN 18th Division, who were outnumbered six to one. For two bloody weeks, severe fighting raged as the ARVN defenders made a last stand to try to block the North Vietnamese advance. By 21 April, however, the exhausted garrison were 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 ago, promising military aid that failed to materialize.
At the time of the peace agreement the United States agreed to replace equipment on a one-by-one basis. But the United States did not keep its word. Is an American's word reliable these days?...The United States did not keep its promise to help us fight for freedom and it was in the same fight that the United States lost 50,000 of its young men.
Having transferred power to Tran Van Huong, he left for Taiwan on 25 April. At the same time, North Vietnamese tanks had reached Bien Hoa and turned toward Saigon, brushing aside isolated ARVN units along the way.
By the end of April, the ARVN had collapsed on all fronts except in the Mekong Delta. Thousands of refugees streamed southward, ahead of the main communist onslaught. 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 VPA shelled the airport and forced its closure. With the air exit closed, large numbers of civilians found that they had no way out.