Shortly before the battle, Colonel Christian de Castries had inspected all the outposts and centers of resistance. He concluded that Gabrielle, guarded by Battalion 5 of the Algerian Infantry Regiment 7 was the best. He awarded them a large sum of money to celebrate. Battalion 5 had always received the most advanced weapons and had been known as the most reliable battalion in combat.

Entrance to an underground tunnel

Gabrielle was an isolated outpost, situated on top of a hill, without any tree or shade. The terrain itself had become a battlefield, surrounded by its own trenches and tunnels and filled with a formidable selection of weapons. The Commander of French artillery, Charles Piroth, had pledged full support for Gabrielle and he would give its defenders the highest priority for artillery reinforcement during the battle.

General Vo Nguyen Giap had named this hill, “Doc Lap”, meaning “Independence”. He assigned the duty of attack to a battalion selected from Division 312 and a battalion selected from Division 308. The Viet Minh’s commander of this combined force was Colonel Vuong Thua Vu, head of 308.

On the second day, March 14, both sides had agreed to a four-hour morning ceasefire to re-organize their troops. It was not until 5 pm that the Viet Minh began shelling Gabrielle. Two regiments from the crack Division 308 joined in the mission at 8 pm. Gabrielle’s defenders suffered huge losses in the night. The French were still shocked and confused at the weight of the Viet Minh artillery and its dominance from the surrounding heights. Muong Thanh airfield was still closed following the attack the previous day and the French had decided not to reopen it. All future supplies for their troops would be dropped in by parachute.

Early the next morning, an artillery shell hit Gabrielle’s headquarters and severely injured its battalion commander and most of his staff. Colonel De Castries ordered a counter attack to save Gabrielle. Responding to the request, Lieutenant Colonel Pierre Langlais, Chief of Operations, asked their 5thVietnamese colonial paratroop battalion for help. It would be too late. They had been loyal to the French but large numbers of them would desert in response to loudspeaker appeals for them to be loyal to their own country. They would be protected by the Viet Minh as they fled from pursuit by the French, intending to shoot deserters. At 8 am the next day, the Algerian battalion fell back, abandoning Gabrielle to the Viet Minh.

A tunnel’s hall way

After five days of heavy fighting, the French had lost their entire northern resistance. The northern “gate” to Dien Bien Phu was now open to the Viet Minh. It had taken Giap’s troops between 6 and 12 hours to destroy each of the northern outposts, Beatrice (Him Lam) and Gabrielle (Doc Lap).

While the French commanders were giving themselves excuses for their defeat, Major General Cogny commented, “Dien Bien Phu is obviously a trap. It’s not a trap for the Viet Minh but it’s a trap for us.” After the fall of the northern outpost, Colonel De Castries isolated himself in his bunker and appeared to have relinquished his command authority.

On the Western side of Dien Bien Phu, the French had reinforced Huguette (Ban Keo) with 7 strongpoints, and Isabelle (Hong Cum) with 5 strongpoints. They had deployed Thai troops (Vietnamese ethnic minority loyal to the French) to defend Huguette. However, the Viet Minh had distributed leaflets to the Thai, telling them that this battle was not for them. In the early hours of March 17, taking advantage of the foggy morning, they all escaped the area. Thai soldiers occupying other Huguette strongpoints lost their morale and slipped away from the battlefield.

Outpost Isabelle (Hong Cum) with 5 strongpoints, was to defend the south side of Muong Thanh airfield. French troops there included the Foreign Legion, Algerians, and Thais. The Viet Minh knew that this outpost had a secret escape route to northern Laos and they made plans to block it. On the Viet Minh side, Colonel Le Chuong of Division 304 was assigned to Hong Cum. A female soldier named Hien celebrated in song the sniper attack strategy (Bắn Bia Sống):

The enemy going out to receive supplies: We shoot!
The enemy going to the creek to bathe: We shoot!
The enemy going out to repair damage to their base: We shoot!
The enemy going out to level our establishment: We shoot!

Since the French relied heavily on parachute supplies, the Viet Minh used anti-aircraft guns to shoot down their planes, severely restricting the drops of food and other necessities to French troops.

To cut off the Isabelle outpost from Muong Thanh airfield, the Vietnamese had begun digging an underground tunnel - going from the eastern side of the mountain range to its western side, and passing under the airfield. Despite air raids and artillery shelling, every evening a group of men and women quietly emerged from the woods, heading toward a creek and arriving at their rendezvous – the secret entrance to the tunnel. The group was divided in half: one with digging tools and the other holding their guns. The following is part of a poem composed by the poet Nguyen Dinh Thi:

The Viet Minh succeeded in isolating Isabelle outpost.  Its parachute supplies would be lost to the Vietnamese. Often, parachutes were blown away by strong wind and their drops would land in the Viet Minh controlled area.