The Battle of Dien Bien Phu was a defining moment in the First Indochina War between the French and the Viet Minh in Vietnam. Taking place from November 20, 1953 through May 7, 1954, it was siege operation by the Viet Minh against the entrenched French forces and a battle of attrition.
The French, under Brigadier General Christian de Castries with some 15,000 troops (French regulars, French Foreign Legion, and indigenous Vietnamese troops fighting on the side of the French) fortified the village and an airstrip. The Viet Minh under General Giap surrounded the village and sealed it off. The French had 28 howitzers of 105mm or greater, but could not match the firepower of 200 guns that Giap was able to bring to bear, including anti-aircraft artillery. Attacks were patiently methodical and incremental. Supply for the French garrison, already inadequate, was cut when the airfield was taken on March 27. Attempts at airdrop failed. Out of 420 French aircraft available to airdrop supplies, 62 were shot down and 107 others damaged. One of the outlying strong points of the defense perimeter finally fell to a combination of Viet Minh mining, artillery fire, and direct assault. The entire complex was overrun on May 7 as the starving French forces ran out of ammunition and surrendered. Only 73 men escaped with 10,000 being captured, half of whom were wounded. It is estimated the Viet Minh suffered 25,000 casualties during the siege.
The French defeat soon led to the end of the First Indochina War, but not the end of warfare in Vietnam which would flare up again and continue for 20 more years.
The Encylopedia of Military History, Dupuy and Dupuy, 1979