Battle of Dien Bien Phu
1954 CE.
Shown on the map at 21.387°, 103.016°.
The Battle of Điện Biên Phủ was a defeat of the French Union forces by the Viet Minh forces in the First Indochina War. It took place between 13 March and 7 May 1954. The French began an operation to insert, and support, their soldiers at Điện Biên Phủ, deep in the autonomous Tai Federation in northwest Tonkin. The operation's purpose was to cut off enemy supply lines into the neighboring Kingdom of Laos (a French protectorate) and draw the Viet Minh into a major confrontation in order to cripple them. The French based their forces in an isolated but well-fortified camp that would be resupplied by air, a strategy adopted based on the belief that the Viet Minh had no anti-aircraft capability. The communist 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 dug tunnels and arranged the guns to target the French positions.
Text from the Wikipedia article Battle of Dien Bien Phu, licensed CC BY-SA 4.0.