The Viet Minh launched a massed assault against the exhausted defenders on the night of 1 May, overrunning "Eliane 1", "Dominique 3", and "Huguette 5", although the French managed to beat back attacks on "Eliane 2". On 6 May, the Viet Minh launched another massed attack against "Eliane 2". The attack included, for the first time, Katyusha rockets. The French artillery used an innovation, firing with a "TOT" (Time On Target) attack, so artillery rounds fired from different positions would strike on target at the same time. This barrage defeated the first assault wave. A few hours later that night, the Viet Minh detonated a mine shaft, blowing "Eliane 2" up. The Viet Minh attacked again, and within a few hours had overrun the defenders.
On 7 May, Giap ordered an all-out attack against the remaining French units with over 25,000 Viet Minh against fewer than 3,000 garrison troops. At 17:00, de Castries radioed French headquarters in Hanoi and talked with Cogny.
De Castries: "The Viets are everywhere. The situation is very grave. The combat is confused and goes on all about. I feel the end is approaching, but we will fight to the finish."
Cogny: "Of course you will fight to the end. It is out of the question to run up the white flag after your heroic resistance."
By nightfall, all French central positions had been captured. The last radio transmission from the French headquarters reported that enemy troops were directly outside the headquarters bunker and that all the positions had been overrun. The radio operator in his last words stated: "The enemy has overrun us. We are blowing up everything. Vive la France!" That night the garrison made a breakout attempt, in the Camarón tradition. While some of the main body managed to break out, none succeeded in escaping the valley. However at "Isabelle", a similar attempt later the same night saw about 70 troops, out of 1,700 men in the garrison, escape to Laos.