In October 1947, Văn Cao went to Việt Bắc for taking part in the resistance war against the French army. In order to reach Việt Bắc, Văn Cao arrived at Phú Thọ, and then walked along the river Lô to the place of the Viet Minh headquarter. During this time, the French carried out Operation Léa to attack the Viet Minh's headquarter, and river Lô was also a place of fierce fighting. But finally, on 24 October 1947, the Viet Minh force gained a decisive victory at the place Đoan Hùng on River Lô, destroy 2 French war-boats and inflicted heavy damages on another two, killed hundred of French troopers. This decisive battle forced the French to withdraw and greatly contributed to the failure of Operation Léa. During the retreat, the French troops raided, burned, destroy a lot of Vietnamese villages along the river banks.