By 1949, during the Viet Minh's transition from guerrilla to regular warfare, he had risen to command the PAVN's first modern infantry division, the 308th, which he led into battle at Dien Bien Phu in 1954.

Hence, he became part of a small nucleus of Chinese-trained officers (Vũ, Nguyễn Sơn, and Lê Thiết Hùng) relied upon by General Giáp and other leaders early in the First Indochina war for their expertise, while due to his connections, he was active in liaising with the People's Republic of China for support.

Furniture was strewn across city streets as makeshift barricades in open view of French forces, and at night on December 19, 1946, some 2,000-10,000 Viet Minh engaged in their first instances of urban warfare, the heaviest fighting occurring in Hanoi's Old Quarter.

The Viet Minh's failure to sabotage the Paul Doumer Bridge nor the military airbase at Gia Lam allowed the French to immediately rush in troops, supplies, and arms into Hanoi, achieving firepower superiority.

From then on, the French slowly recaptured Hanoi from its poorly-armed defenders in a battle marred by civilian massacres and torture committed by both factions, and the Old Quarter was levelled to rubble by airstrikes and artillery.

His defence allowed the DRV government to evacuate in an orderly manner, taking with them machinery, medical equipment, printing presses, and even the Voice of Vietnam transmitters into the countryside.

The unexpected PLA successes meant that the PAVN could now transition from guerrilla tactics to modern, conventional warfare in line with Mao's "General Counteroffensive" principles.

They expanded their General Staff, recruiting more logistics, intelligence, and instruction personnel, and built a sophisticated officer corps trained to fight pitched, coordinated battles.

[5]: 113–14 After initially poor outcomes, his division achieved multiple victories in the following years: in 1952 they overran an outpost at Nghia Lo in just one hour,[5]: 322  then fended off Operation Lorraine, ambushing retreating convoys to inflict high French losses.

[5]: 403–7  A couple of weeks later on March 28–31, they took part in the battle for five hills east of Dien Bien Phu, but failed to take Eliane 2 while Huguette 7 was recaptured by the defenders,[5]: 470–81  after which Giap ordered all divisions to dig in around the remaining French forces.