SAIGON -- Tank-led North Vietnamese troops smashed into the coastal headquarters city of Nha Trans Tuesday, forcing South Vietnamese defenders to abandon the key provincial capital that was once the home of the U.S. Green Berets.
Nha Trang, 183 miles northeast of Saigon, was the third provincial capital to lost In 24 hours by the South Vietnamese in the face of a Communist blitzkrieg the central coast through crumbling defenses toward an increasingly Jittery Saigon.
Late last night, meanwhile, it was reported defenses began crumbling at Cam Rahn Bay, once so safe from attack that was chosen for war zone visits by President Lyndon B. Johnson.
The United States sent 700 Marines from Okinawa to South Vietnam Tuesday to keep order on the four ships heading Vietnam to help in the evacuation of South Vietnamese troops became disorderly on a civilian evacuation ship Monday and shot and raped civilians. The Pentagon emphasized the Marines would be used only for "ship security and shipboard evacuation control."
The three abandoned capitals were Qui Nhon, Tuy Hoa and Nha Trang on the ranging up to 250 miles northeast of Saigon. The Communists now control 15 provinces -- roughly about two-thirds of South Vietnamese territory.
Pressure for the removal of President Nguyen Van Thieu from office mounted Tuesday. Sen. Vu Van Mau, former foreign minister and spokesman of a radical Buddhist movement, demanded his immediate resignation.
Coup rumors swept the capital as the situation deteriorated. Hundreds of foreign residents of Saigon swamped immigration offices trying to obtain exit visas.
Scenes reminiscent of the panicky evacuation of Da Nang lost weekend were replayed on the tarmac at Nha Trang Tuesday.
Fist fights broke out as people scrambled for evacuation planes. Eyewitnesses said some parents literally threw their children into plane doorways.
In other developments:
-- A tearful President Lon Nol left embattled Cambodia for exile. Lon Nol, 62, has led the Cambodian government for five years since the overthrow of Prince Norodom Sihanouk, flew to Indonesia via Thailand, and then on to Bali the first leg of what was described as tour destined to take him to the United States.
-- The White House said President Ford and Secretary of State Henry A. Kissinger are using diplomatic channels in an effort to stop the North Vietnamese of South Vietnam.