Editing Battle of Dien Bien Phu (section)

=== Lull ===
A lull in fighting occurred from March 17 to March 30. The Viet Minh further encircled the French central area (formed by the strong points ''Huguette'', ''Dominique'', ''Claudine'', and ''Eliane''), effectively cutting off ''Isabelle'' and its 1,809 personnel to the south.{{sfn|Fall|1967|p=279}} During this lull, the French suffered from a serious crisis of command. Senior officers with the garrison and Cogny in Hanoi began to feel that de Castries was incompetent in defending Dien Bien Phu. After the loss of the northern outposts, he isolated himself in his bunker, ''de facto'' shirking his command of the situation.<ref name="d241">{{harvnb|Davidson|1988|pp=240–241}}</ref> On 17 March, Cogny attempted to fly into Điện Biên Phủ to take command, but his plane was driven off by anti-aircraft fire. He considered parachuting into the encircled garrison, but his staff talked him out of it.<ref name="d241" />

[[File:Xung phong.jpg|thumb|280px|Viet Minh soldiers launching an assault during the battle]]
De Castries' seclusion in his bunker, combined with his superiors' inability to replace him, created a leadership vacuum in the French command. On 24 March, an event took place which later became a matter of historical debate. The historian [[Bernard Fall]] records, based on Langlais' memoirs, that Langlais and his fellow paratroop commanders, all fully armed, confronted de Castries in his bunker on 24 March. They told him he would retain the appearance of command, but that Langlais would exercise it.{{sfn|Fall|1967|p=177}} De Castries is said by Fall to have accepted the arrangement without protest, although he did exercise some command functions thereafter. Phillip Davidson stated that the "truth would seem to be that Langlais did take over effective command of Dien Bien Phu, and that Castries became 'commander emeritus' who transmitted messages to Hanoi and offered advice about matters in Dien Bien Phu".{{sfn|Davidson|1988|p=243}} [[Jules Roy]], however, makes no mention of this event, and [[Martin Windrow]] argues that the "paratrooper putsch" is unlikely to have ever happened. Both historians record that Langlais and [[Marcel Bigeard]] were known to be on good terms with their commanding officer.{{sfn|Windrow|2004|pp=441–44}}

French aerial resupply took heavy losses from Viet Minh machine guns near the landing strip. On 27 March, the Hanoi air transport commander, Nicot, ordered that all supply deliveries be made from {{cvt|2000|m}} or higher; losses were expected to remain heavy.{{sfn|Davidson|1988|p=244}} The following day, De Castries ordered an attack against the Viet Minh AA machine guns {{cvt|3|km}} west of Điện Biên Phủ. Remarkably, the attack was a complete success, with 350 Viet Minh's casualties and seventeen [[DShK|12.7mm AA machine guns]] destroyed (French estimate), while the French lost 20 killed and 97 wounded.{{sfn|Davidson|1988|pp=244–45}}