Dienbienphu or Dien Bien Phu (dyĕn´byĕn´fōō´), former French military base, N Vietnam, near the Laos border. It was the scene in 1954 of the last great battle between the French and the Viet Minh forces of Ho Chi Minh in Indochina. The French occupied the base by parachute drop in Nov., 1953; this move prevented a Viet Minh thrust into Laos and provided support for indigenous forces opposing the Viet Minh in that area. Although the base could be supplied only by air, the French military felt its position was tenable. Weary of inconclusive guerrilla warfare, they were willing to invite an open Viet Minh attack in an area where their superior weaponry could be used to full advantage. The Viet Minh army, under the command of Gen. Vo Nguyen Giap, chose to engage the French, and by Mar., 1954, some 49,500 Viet Minh troops had encircled Dienbienphu, where some 13,000 soldiers, under the leadership of Col. (later Gen.) Christian de Castries, were firmly entrenched in strong positions. The first Viet Minh assault came on Mar. 13, and by the end of April, despite massive French air bombardment, the French defense area had been reduced to 2 sq mi (5 sq km). Desperate pleas for U.S. intervention were unsuccessful, and on May 7, after a 56-day siege, the French positions fell. This defeat signaled the end of French power in Indochina.