The French established the fortification to guard the essential lines of communication between the cities of Hanoi and Haiphong and to provide security for the densely populated and economically important Delta area against attacks by both the Việt Minh and any potential invasion from Communist China.
In addition a defensive redoubt was to be constructed around a 22 miles (35 km) radius from the port of Haiphong ensuring its safety from artillery attack.
All these new defensive lines were to be connected by roads capable of bearing 30-ton tanks.
[1]: 116 While the De Lattre Line provided some degree of security and formed an anchor point for French mobile operations outside the Delta, it was far from impenetrable and entire Việt Minh combat units could be easily infiltrated through the gaps between strongpoints.
[1]: 213 Following the withdrawal of the French from northern Vietnam in October 1954 the De Lattre Line was abandoned.