French army officer who commanded during World War II and later in the Indochina War.

Castries was born into a distinguished military family and enlisted in the army at the age of 19. He was sent to the Saumur Cavalry School and in 1926 was commissioned an officer, but he later resigned to devote himself to equestrian sports. After rejoining the army at the start of World War II, he was captured (1940), escaped from a German prison-of-war camp (1941), and fought with the Allied forces in North Africa, Italy, and southern France.

In 1946 Castries, soon to become a lieutenant colonel, was sent to Indochina. He was wounded and spent a year recuperating in France before returning to Vietnam as a full colonel. In December 1953 he was charged with defending Dien Bien Phu (Dien Bien Phu, Battle of) against overwhelming odds and was given a field promotion to brigadier general. After an eight-week siege, the garrison was defeated. The French surrender to the Viet Minh forces on May 7, 1954, effectively ended the first Indochina War and the French colonial presence in Southeast Asia. Castries was held prisoner for four months while an armistice agreement was reached in Geneva. He retired from the military in 1959.