In the waning moments of the U.S. war in Vietnam, U.S. Ambassador Graham Martin called for an evacuation of the U.S. Embassy in Saigon. North Vietnamese forces were rolling south toward the city, and thousands of Americans and South Vietnamese needed to be evacuated.

What followed was Operation Frequent Wind. The U.S. military pulled more than 7,000 people from Saigon, now known as Ho Chi Minh City, in helicopters on April 29 and 30, 1975. Images of helicopters lifting off from the roof of the embassy remain burned in the memory of many Americans, a symbol of the pain and frustration of the Vietnam War.

To mark the anniversary, here are images from that operation. The United States used so many helicopters to evacuate people, some were pushed overboard from Navy ships off the coast of Vietnam to allow more to land. Thousands of South Vietnamese who had helped the United States were left behind.

Vietnam on April 30, commemorated the 40th anniversary of the fall of Saigon with a military parade in what is now called Ho Chi Minh City. Some 6,000 soldiers and civilians marched towards the Presidential Palace. (Reuters)