The Battle of Dien Bien Phu was a climactic confrontation of the First Indochina War that took place between 13 March and 7 May 1954. It was fought between the French Union's colonial Far East Expeditionary Corps and Viet Minh communist revolutionaries. The United States was officially not a party to the war, but it was secretly involved by providing financial and material aid, which included CIA contracted American personnel participating in the battle.

The French began an operation to insert, then support, their soldiers at Điện Biên Phủ, deep in the west of Tonkin, up in the hills of northwestern Vietnam. The operation's purpose was to cut off Viet Minh supply lines into the neighboring Kingdom of Laos (a French ally), and draw the Viet Minh into a major confrontation in order to cripple them. The plan was to resupply the French position by air - based on the belief that the Viet Minh had no anti-aircraft capability. The Viet Minh, however, under General Võ Nguyên Giáp, surrounded and besieged the French. They brought in vast amounts of heavy artillery (including anti-aircraft guns) and managed to move these bulky weapons through difficult terrain up the rear slopes of the mountains. They then dug tunnels through the mountains and arranged the guns to target the French position.

In March, a massive artillery bombardment by the Viet Minh ensued. The strategic positioning of their artillery made it nearly impervious to French counter-battery fire. Tenacious fighting on the ground ensued, reminiscent of the trench warfare of World War I. At times, the French repulsed Viet Minh assaults on their positions while supplies and reinforcements were delivered by air. As key positions were overrun, the perimeter contracted, and the air resupply on which the French had placed their hopes became impossible. As the Viet Minh anti-aircraft fire took its toll, fewer and fewer of those supplies reached the French. The garrison was overrun in May after a two-month siege, and most of the French forces surrendered. A few of them escaped to Laos. The French government in Paris then resigned, and the new Prime Minister, the left-of-centre Pierre Mendès France, supported French withdrawal from Indochina.

The Battle of Điện Biên Phủ was decisive; the war ended shortly afterward and the 1954 Geneva Accords were signed. France agreed to withdraw its forces from all its colonies in French Indochina, while stipulating that Vietnam would be temporarily divided at the 17th parallel, with control of the north given to the Viet Minh as the Democratic Republic of Vietnam under Ho Chi Minh, and the south becoming the State of Vietnam, nominally under Emperor Bảo Đại.