1. A continuous line of trenches over the whole front, comprising on a limited depth two or three trenches, joined by numerous communicating trenches (boyaux), and separated by 100 to 300 metres, each one often protected by a wire entanglement.
2. Centers of resistance, comprising large villages, woods, or immense field works, consisting of a network of trenches which are very strongly organized and in which machine guns under cupolas as well as pieces of artillery are mounted.
Such are, for example, the Labyrinth and Ouvrages Blancs of Neuville. These centers of resistance are separated by intervals of 800 to 1,500 metres; they mutually flank each other, and their intervals are generally guarded by closed works.
3. A second line of defense, which is not always continuous.
PREPARATION BY THE ARTILLERY.
In order to attack with minimum loss, the infantry-requires that the artillery in its preparation carry through the following program:
(a) Destroy the wire entanglements.
(b) Neutralize or destroy the defenders of the trenches.
(c) Prevent the artillery from coming into action.
(d) Prevent the bringing up of reserves.