Operating from bases in the People's Republic of China, Việt Minh troops under Giáp constantly raided French outposts along Route Coloniale 4.

The French occupied most of the country, but the Việt Minh held considerable portions of the countryside that allowed quick and easy access to various crucial points should the need arise.

Four of the five Vietnamese divisions were roughly 150 miles (241 km) north of Hanoi, stationed around the Việt Bắc region near the Chinese border.

Giáp decided to strike straight for Hanoi and chose Vĩnh Yên, 30 miles northwest of the capitol and the tip of the French defensive triangle, for the main blow.

Giáp hoped to drive a wedge between the two forces by pinning GM 3 against the Dam Vac lake to the south and then defeating the French in detail.

The 308th Division made a diversionary attack on Bao Chuc, a small outpost about two miles north of Vĩnh Yên.

A series of heavy air strikes and artillery barrages eventually allowed GM 3 to disengage and return to Vĩnh Yên, but not before it had lost an entire battalion and had another severely damaged.

De Lattre replied by ordering the largest French air strike of the entire war, in which napalm was used for the first time on a large scale.