refugees from communism. In Vietnamese, it is also known by the neutral name "April 30, 1975 incident" () or simply "April 30" (). North Vietnamese advance The rapidity with which the South Vietnamese position collapsed in 1975 was surprising to most American and South Vietnamese observers, and probably to the North Vietnamese and their allies as well. For instance, a memo prepared by the Central Intelligence Agency (CIA) and U.S. Army Intelligence, published on 5 March, indicated that South Vietnam could hold out through the current dry season—i.e., at least until 1976. These predictions proved to be grievously in error. Even as that memo was being released, General Dũng was preparing a major offensive in the Central Highlands of Vietnam, which began on 10 March and led to the capture of Buôn Ma Thuột. The ARVN began a disorderly and costly retreat, hoping to redeploy its forces and hold the southern part of South Vietnam, south of the 13th parallel. Supported by artillery and armor, the PAVN continued to march towards Saigon, capturing the major cities of northern South Vietnam at the end of March—Huế on the 25th and Đà Nẵng on the 28th. Along the way, disorderly South Vietnamese retreats and the flight of refugees—there were more than 300,000 in Đà Nẵng—damaged South Vietnamese prospects for a turnaround. After the loss of Đà Nẵng, those prospects had already been dismissed as nonexistent by American CIA officers in Vietnam, who believed that nothing short of B-52 strikes against Hanoi could possibly stop the North Vietnamese. By 8 April, the North Vietnamese Politburo, which in March had recommended caution to Dũng, cabled him to demand "unremitting vigor in the attack all the way to the heart of Saigon." On 14 April, they renamed the campaign the "Hồ Chí Minh campaign", after revolutionary leader Hồ Chí Minh, in hopes of wrapping it up before his birthday on 19 May. Meanwhile, South Vietnam failed to garner any significant increase in military aid from the United States, snuffing out President Nguyễn Văn Thiệu's hopes for renewed American support. On 9 April, PAVN forces reached Xuân Lộc, the last line of defense before Saigon, where the ARVN 18th Division made a last stand and held the city through fierce fighting for 11 days. The ARVN finally withdrew from Xuân Lộc on 20 April having inflicted heavy losses on the PAVN, and President Thiệu resigned on