The Liberation or (depending on the context) the Fall of Saigon   was the capture of Saigon, the capital of South Vietnam, by the People's Army of Vietnam and the National Liberation Front of South Vietnam (also known as the Việt Cộng) on 30 April 1975. The event marked the end of the Vietnam War and the start of a transition period to the formal reunification of Vietnam under the Socialist Republic.
North Vietnamese forces, under the command of General Văn Tiến Dũng, began their final attack on Saigon on April 29, 1975, with the Army of the Republic of Vietnam (ARVN) forces commanded by General Nguyễn Văn Toàn suffering a heavy artillery bombardment. This bombardment at the Tân Sơn Nhất Airport killed the last two American servicemen to die in Vietnam, Charles McMahon and Darwin Judge. By the afternoon of the next day, North Vietnamese troops had occupied the important points of the city and raised their flag over the South Vietnamese presidential palace. The South Vietnamese government capitulated shortly afterwards. The city was renamed Hồ Chí Minh City, after the Democratic Republic's late President Hồ Chí Minh.
The capture of the city was preceded by the evacuation of almost all the American civilian and military personnel in Saigon, along with tens of thousands of South Vietnamese civilians who had been associated with the southern regime.  The evacuation culminated in Operation Frequent Wind, the largest helicopter evacuation in history. In addition to the flight of refugees, the end of the war and the institution of new rules by the communists contributed to a decline in the city's population.
Various names have been applied to these events. The Vietnamese government officially calls it the " Day of liberating the South for national reunification " (Vietnamese: Giải phóng miền Nam, thống nhất đất nước) or "Liberation Day" (Ngày Giải Phóng), but the term "Fall of Saigon" is commonly used in Western accounts. It is called the " Ngày mất nước " (Day we Lost the Country) , " Tháng Tư Đen " (Black April) ,       " Ngày Quốc Nhục " (National Day of Shame) , or " Ngày Quốc Hận " (National Day of Resentment)      by many Overseas Vietnamese who were refugees from communism.
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 CIA and U.S. Army Intelligence and published on March 5 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, perhaps an enclave south of the 13th parallel. 
Supported by artillery and armor, the North Vietnamese 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 Central Intelligence Agency officers in Vietnam, who believed that nothing short of B-52 strikes against Hanoi could possibly stop the North Vietnamese. 
By April 8, 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 April 14, 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 May 19.  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 April 9, 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 several days. The PAVN finally overran Xuân Lộc on April 20 despite heavy losses, and on April 21 President Thiệu resigned in a tearful televised announcement in which he denounced the United States for failing to come to the aid of the South.  The North Vietnamese front line was now just 26 miles (42 km) from downtown Saigon. The victory at Xuân Lộc, which had drawn many South Vietnamese troops away from the Mekong Delta area, opened the way for PAVN to encircle Saigon, and they soon did so, moving 100,000 troops in position around the city by April 27. With the ARVN having few defenders, the fate of the city was effectively sealed.
The ARVN III Corps commander, General Toan, had organized five centers of resistance to defend the city. These fronts were so connected as to form an arc enveloping the entire area west, north, and east of the capital. The Cu Chi front, to the northwest, was defended by the 25th Division; the Binh Duong front, to the north, was the responsibility of the 5th Division; the Bien Hoa front, to the northeast, was defended by the 18th Division; the Vung Tau and 15 Route front, to the southeast, were held by the 1st Airborne Brigade and one battalion of the 3rd Division; and the Long An front, for which the Capital Military District Command was responsible, was defended by elements of the re-formed 22nd Division. South Vietnamese defensive forces around Saigon totaled approximately 60,000 troops. However, as the exodus made it into Saigon, along with them were many ARVN soldiers, which swelled the "men under arm" in the city to over 250,000. These units were mostly battered and leaderless, which threw the city into further anarchy.
The rapid North Vietnamese advances of March and early April led to increased concern in Saigon that the city, which had been fairly peaceful throughout the war and whose people had endured relatively little suffering, was soon to come under direct attack.  Many feared that once the communists took control of the city, a bloodbath of reprisals would take place. In 1968, PAVN and National Liberation Front (NLF) forces had occupied Huế for close to a month. After the communists were repelled, American and ARVN forces had found mass graves. A study prepared for the U.S. mission in Vietnam indicated that the communists had targeted ARVN officers, Roman Catholics, intellectuals and businessmen, and other suspected counterrevolutionaries.  More recently, eight Americans captured in Buôn Ma Thuột had vanished and reports of beheadings and other executions were filtering through from Huế and Đà Nẵng, mostly spurred on by government propaganda.  Most Americans and citizens of other countries allied to the United States wanted to evacuate the city before it fell, and many South Vietnamese, especially those associated with the United States or South Vietnamese government, wanted to leave as well.
As early as the end of March, some Americans were leaving the city. For instance, ten families departed on March 31.  Flights out of Saigon, lightly booked under ordinary circumstances, were full. Throughout April the speed of the evacuation increased, as the Defense Attaché’s Office (DAO) began to fly out nonessential personnel. Many Americans attached to the DAO refused to leave without their Vietnamese friends and dependents, who included common-law wives and children. It was illegal for the DAO to move these people to American soil, and this initially slowed down the rate of departure, but eventually the DAO began illegally flying undocumented Vietnamese to Clark Air Force Base in the Philippines.
On April 3, President Gerald Ford announced “ Operation Babylift ”, which would evacuate about 2,000 orphans from the country. One of the Lockheed C-5 Galaxy planes involved in the operation crashed, killing 155 passengers and crew and seriously reducing the morale of the American staff. In addition to the over 2,500 orphans evacuated by Babylift, Operation New Life resulted in the evacuation of over 110,000 Vietnamese refugees. The final evacuation was Operation Frequent Wind which resulted in 7,000 people being evacuated from Saigon by helicopter.
American administration plans for final evacuation
By this time the Ford administration had also begun planning a complete evacuation of the American presence. The planning was complicated by practical, legal, and strategic concerns. The administration was divided on how swift the evacuations should be. The Pentagon sought to evacuate as fast as possible, to avoid the risk of casualties or other accidents. The U.S Ambassador to South Vietnam, Graham Martin, was technically the field commander for any evacuation since evacuations are part of the purview of the State Department. Martin drew the ire of many in the Pentagon by wishing to keep the evacuation process as quiet and orderly as possible. His desire for this was to prevent total chaos and to deflect the real possibility of South Vietnamese turning against Americans and to keep all-out bloodshed from occurring.
Ford approved a plan between the extremes in which all but 1,250 Americans—few enough to be removed in a single day’s helicopter airlift—would be evacuated quickly; the remaining 1,250 would leave only when the airport was threatened. In between, as many Vietnamese refugees as possible would be flown out.
American evacuation planning was set against other administration policies. Ford still hoped to gain additional military aid for South Vietnam. Throughout April, he attempted to get Congress behind a proposed appropriation of $722 million, which might allow for the reconstitution of some of the South Vietnamese forces that had been destroyed. Kissinger was opposed to a full-scale evacuation as long as the aid option remained on the table because the removal of American forces would signal a loss of faith in Thiệu and severely weaken him.
There was also a concern in the administration over whether the use of military forces to support and carry out the evacuation was permitted under the newly passed War Powers Act. Eventually White House lawyers determined that the use of American forces to rescue citizens in an emergency was unlikely to run afoul of the law, but the legality of using military assets to withdraw refugees was unknown.
While American citizens were generally assured of a simple way to leave the country just by showing up to an evacuation point, South Vietnamese who wanted to leave Saigon before it fell often resorted to independent arrangements. The under-the-table payments required to gain a passport and exit visa jumped sixfold, and the price of seagoing vessels tripled. Those who owned property in the city were often forced to sell it at a substantial loss or abandon it altogether; the asking price of one particularly impressive house was cut 75 percent within a two-week period. American visas were of enormous value, and Vietnamese seeking American sponsors posted advertisements in newspapers. One such ad read: “Seeking adoptive parents. Poor diligent students” followed by names, birthdates, and identity card numbers.
Political movements and attempts at a negotiated solution
As the North Vietnamese chipped away more and more at South Vietnam, internal opposition to President Thiệu continued to accumulate. For instance, in early April, the Senate unanimously voted through a call for new leadership, and some top military commanders were pressing for a coup. In response to this pressure, Thiệu made some changes to his cabinet, and Prime Minister Trần Thiện Khiêm resigned. This did little to reduce the opposition to Thiệu. On April 8 a South Vietnamese pilot and communist spy, Nguyễn Thành Trung, bombed the presidential palace and then flew to a PAVN-controlled airstrip; Thiệu was not hurt. 
Many in the American mission—Martin in particular—along with some key figures in Washington, believed that negotiations with the communists were possible, especially if Saigon could stabilize the military situation. Ambassador Martin’s hope was that North Vietnam’s leaders would be willing to allow a “phased withdrawal” whereby a gradual departure might be achieved in order to allow helpful locals and all Americans to leave (along with full military withdrawal) over a period of months.
Opinions were divided on whether any government headed by Thiệu could affect such a political solution.  The Provisional Revolutionary Government ’s foreign minister had, on April 2, indicated that the PRG might negotiate with a Saigon government that did not include Thiệu. Thus, even among Thiệu’s supporters, pressure was growing for his ouster. 
President Thiệu resigned on April 21. His remarks were particularly hard on the Americans, first for forcing South Vietnam to accede to the Paris Peace Accords, second for failing to support South Vietnam afterwards, and all the while asking South Vietnam “to do an impossible thing, like filling up the oceans with stones.”  The presidency was turned over to Vice President Trần Văn Hương. The view of the North Vietnamese government, broadcast by Radio Hanoi, was that the new regime was merely “another puppet regime.” 
- All times given are Saigon time.
On April 27, Saigon was hit by three NVA rockets – the first in more than 40 months.
Operation Frequent Wind
Before daybreak on April 29, Tan Son Nhat Airport was hit by rockets and heavy artillery. In the initial shelling, C-130E, 72-1297 , c/n 4519, of the 314th Tactical Airlift Wing, and flown by a crew from the 374th Tactical Airlift Wing out of Clark Air Base, Philippines, was destroyed by a rocket while taxiing to pick up evacuees. The crew evacuated the burning aircraft on the taxiway and departed the airfield on another C-130 that had previously landed. The continuing rocket fire and debris on the runways caused General Homer D. Smith, the U.S. defense attaché in Saigon, to advise Ambassador Martin that the runways were unfit for use and that the emergency evacuation of Saigon would need to be completed by helicopter. 
Originally, Ambassador Martin had fully intended to effect the evacuation by use of fixed-wing aircraft from the base. This plan was altered at a critical time when a South Vietnamese pilot decided to defect, and jettisoned his ordnance along the only runways still in use (which had not yet been destroyed by shelling).
Under pressure from Kissinger, Martin forced Marine guards to take him to the air base in the midst of continued shelling, so he might personally ascertain the situation. After seeing that fixed-wing departures were not an option (a mammoth decision Martin did not want to make without firsthand responsibility in case the helicopter lift failed), Martin gave the green light for the helicopter evacuation to begin in earnest.
Reports came in from the outskirts of the city that the North Vietnamese were moving.  At 10:48 a.m., Martin relayed to Kissinger his desire to activate "the FREQUENT WIND" evacuation plan; Kissinger gave the order three minutes later. The American radio station began regular play of Irving Berlin's " White Christmas," the signal for American personnel to move immediately to the evacuation points.  
Under this plan, CH-53 and CH-46 helicopters were used to evacuate Americans and friendly Vietnamese to ships, including the Seventh Fleet, in the South China Sea.  The main evacuation point was the DAO Compound at Tan Son Nhat; buses moved through the city picking up passengers and driving them out to the airport, with the first buses arriving at Tan Son Nhat shortly after noon. The first CH-53 landed at the DAO compound in the afternoon, and by the evening, 395 Americans and more than 4,000 Vietnamese had been evacuated. By 23:00 the U.S. Marines who were providing security were withdrawing and arranging the demolition of the DAO office, American equipment, files, and cash. Air America UH-1s also participated in the evacuation.
The original evacuation plans had not called for a large-scale helicopter operation at the United States Embassy, Saigon. Helicopters and buses were to shuttle people from the Embassy to the DAO Compound. However, in the course of the evacuation it turned out that a few thousand people were stranded at the embassy, including many Vietnamese. Additional Vietnamese civilians gathered outside the Embassy and scaled the walls, hoping to claim refugee status. Thunderstorms increased the difficulty of helicopter operations. Nevertheless, the evacuation from the Embassy continued more or less unbroken throughout the evening and night. At one point a Japanese photojournalist taking pictures of the evacuees was caught up in a crowd of them rushing onto a helicopter and was accidentally evacuated along with them. He subsequently languished for several weeks at refugee camp in Guam before being allowed to leave for Japan.
At 03:45 on the morning of April 30, the refugee evacuation was halted. Ambassador Martin had been ordering that South Vietnamese be flown out with Americans up to that point. Kissinger and Ford quickly ordered Martin to evacuate only Americans from that point forward.
Reluctantly, Martin announced that only Americans were to be flown out, due to worries that the North Vietnamese would soon take the city and the Ford administration's desire to announce the completion of the American evacuation. Ambassador Martin was ordered by President Ford to board the evacuation helicopter.
The call sign of that helicopter was "Lady Ace 09", and the pilot carried direct orders from President Ford for Ambassador Martin to be on board. The pilot, Gerry Berry, had the orders written in grease-pencil on his kneepads. Ambassador Martin's wife, Dorothy, had already been evacuated by previous flights, and left behind her personal suitcase so a South Vietnamese woman might be able to squeeze on board with her.
"Lady Ace 09" from HMM-165 and piloted by Berry, took off around 05:00 - had Martin refused to leave, the Marines had a reserve order to arrest him and carry him away to ensure his safety. The embassy evacuation had flown out 978 Americans and about 1,100 Vietnamese. The Marines who had been securing the Embassy followed at dawn, with the last aircraft leaving at 07:53. A few hundred Vietnamese were left behind in the embassy compound, with an additional crowd gathered outside the walls.
The Americans and the refugees they flew out were generally allowed to leave without intervention from either the North or South Vietnamese. Pilots of helicopters heading to Tan Son Nhat were aware that PAVN anti-aircraft guns were tracking them, but they refrained from firing. The Hanoi leadership, reckoning that completion of the evacuation would lessen the risk of American intervention, had instructed Dũng not to target the airlift itself. Meanwhile, members of the police in Saigon had been promised evacuation in exchange for protecting the American evacuation buses and control of the crowds in the city during the evacuation.
Although this was the end of the American military operation, Vietnamese continued to leave the country by boat and, where possible, by aircraft. South Vietnamese pilots who had access to helicopters flew them offshore to the American fleet, where they were able to land; those who left South Vietnam this way include at least General Nguyễn Cao Kỳ. Most of the South Vietnamese helicopters were dumped into the ocean to make room on the decks for more aircraft. South Vietnamese fighters and other small planes also landed on American carriers.
Ambassador Martin was flown out to the USS Blue Ridge, where he pleaded for helicopters to return to the Embassy compound to pick up the few hundred remaining hopefuls waiting to be evacuated. Although his pleas were overruled by President Ford, Martin was able to convince the Seventh Fleet to remain on station for several days so any locals who could make their way to sea via boat or aircraft might be rescued by the waiting Americans.
Many Vietnamese nationals who were evacuated were allowed to enter the United States under the Indochina Migration and Refugee Assistance Act.
Decades later, when the U.S. government reestablished diplomatic relations with Vietnam, the former embassy was returned to the United States. The historic staircase that led to the rooftop helicopter pad was salvaged and is on permanent display at the Gerald R. Ford Museum in Grand Rapids, Michigan.
Capitulation of South Vietnam
With his overtures to the north rebuffed out of hand, Tran resigned on 28 April and was succeeded by General Duong Van Minh. Duong took over a regime that was by this time in a state of utter collapse. However, he had longstanding ties with the Communists, and it was hoped he could negotiate a cease-fire.
But Hanoi was in no mood to negotiate. On 28 April PAVN forces fought their way into the outskirts of the city. At the Newport Bridge ( Cầu Tân Cảng ), about three miles (five kilometers) from the city center,  South Vietnamese soldiers battled with PAVN troops attempting to control the span, cutting the city's last overland connection to the south and thereby gaining immediate access to downtown. Later that afternoon, as President Minh finished his acceptance speech, a formation of four A-37s, captured from the Republic of Vietnam Air Force, bombed Tan Son Nhut airport. As Bien Hoa was falling, General Toan fled to Saigon, informing the government that most of the top ARVN leadership had virtually resigned themselves to defeat.
At 06:00 on April 29, General Dung was ordered by the Politburo to "strike with the greatest determination straight into the enemy's final lair." At the same time, there were still many Air America aircraft at Tan Son Nhat. Shortly after 7:35 the many UH-1 Hueys began their shuttles from the many rooftop pads around town out to the U.S. Navy ships offshore. The fixed-wing aircraft each had assigned pilots, but due to the confusion, many pilots could not get to the airport. Captain E. G. Adams was assigned to pilot a Volpar Beech but when he was the last pilot on the Air America ramp (all other personnel had gone over to the MACV HQ), and there was a C-46 aircraft full of refugees parked there, Adams boarded that aircraft (a 52-passenger configured ship with 152 people on board) and departed on it, so it thus became the last fixed-wing aircraft to depart Saigon during the evacuation, dodging the burning aircraft on the Main Ramp and on Runway 36.
After one day of bombardment and general offensive, the North Vietnamese were ready to make their final push into the city. In the early hours of April 30, Dung received orders from the Politburo to attack. He then ordered his field commanders to advance directly to key facilities and strategic points in the city. The first PAVN unit to enter the city was the 324th Division. By daybreak, it was obvious that the ARVN's position was untenable. At 10:24, Minh announced an unconditional surrender. He ordered all ARVN troops "to cease hostilities in calm and to stay where they are," while inviting the Provisional Revolutionary Government to engage in "a ceremony of orderly transfer of power so as to avoid any unnecessary bloodshed in the population." 
However, the North Vietnamese were in an overwhelmingly dominant position, and were not interested in a peaceful transfer of power. PAVN T-54/55 tanks under the command of Colonel Bùi Tín burst through the gates of the Independence Palace around noon. They found Minh and 30 of his advisors sitting around the big oval table in the cabinet room, waiting for them. As they entered, Minh said "The revolution is here. You are here."  He added, "We have been waiting for you so that we could turn over the government." Tín curtly replied, "There is no question of your transferring power. Your power has crumbled. You cannot give up what you do not have." Later that afternoon, Minh went on the radio for the final time and announced, "I declare [that] the Saigon government is completely dissolved at all levels."  The Vietnam War was over.
Turnover of Saigon
The communists renamed the city after Ho Chi Minh, former President of North Vietnam, although this name was not frequently used outside official business. Order was slowly restored, although the by-then-deserted U.S. embassy was looted, along with many other businesses. Communications between the outside world and Saigon were cut. The Communist party machinery in South Vietnam was weakened, owing in part to the Phoenix Program, so the North Vietnamese army was responsible for maintaining order and General Trần Văn Trà, Dung's administrative deputy, was placed in charge of the city. The new authorities held a victory rally on May 7.
One objective of the communist government was to reduce the population of Saigon, which had become swollen with an influx of people during the war and was now overcrowded with high unemployment. "Re-education classes" for former soldiers in the ARVN indicated that in order to regain full standing in society they would need to move from the city and take up farming. Handouts of rice to the poor, while forthcoming, were tied to pledges to leave Saigon for the countryside. According to the Vietnamese government, within two years of the capture of the city one million people had left Saigon, and the state had a target of 500,000 further departures.
Following the end of the war, according to official and non-official estimates, between 200,000 and 300,000 South Vietnamese were sent to reeducation camps, where many endured torture, starvation, and disease while being forced to perform hard labor.   
April 30 is a public holiday in Vietnam, known as Reunification Day (though the official reunification of the nation actually occurred on 2 July 1976) or Liberation Day (Ngày Giải Phóng).
Whether the evacuation had been successful or not has been questioned following the end of the war. Operation Frequent Wind was generally assessed as an impressive achievement—Van Tien Dung stated this in his memoirs and The New York Times described it as being carried out with "efficiency and bravery". On the other hand, the airlift was also criticized for being too slow and hesitant, and that it was inadequate in removing Vietnamese civilians and soldiers connected with the American presence.
The U.S. State Department estimated that the Vietnamese employees of the American Embassy in Vietnam, past and present, and their families totaled 90,000 people. In his testimony to Congress, Martin asserted that 22,294 such people were evacuated by the end of April. Of the tens of thousands of former South Vietnamese collaborators with the State Department, Central Intelligence Agency, U.S. military, and countless armed forces officers and personnel in risk of reprisal, nothing of this subject matter is known. In 1977, National Review alleged that some 30,000 South Vietnamese had been systematically killed using a list of CIA informants left behind by the US embassy.
Among former South Vietnamese expatriates in the United States the week of April 30 is referred to as " Black April " and is used as a time of lamentation for the fall of Saigon. The event is approached from different perspectives, with arguments that the date was a sign of American abandonment, or as a memorial for the war and for the mass exodus as a whole.