3. The trenches of the second line.
By a study of the text preceding this you must realize that in the defense of these objectives there will be employed artillery, rifles, grenades and machine guns.
Artillery Preparation
The first phase of the attack is the artillery preparation. In order that the infantry may make the attack with a minimum of losses, the artillery must have destroyed the wire entanglements and obstacles that obstruct the advance, or at least have sufficiently breached them to permit their being negotiated. The destruction of these obstacles is never complete. It would require too great an expenditure of ammunition. The infantry occupying the hostile trenches must be simply overwhelmed with artillery fire so that they will be unable to man the parapets when the assault is launched. During the artillery preparation the hostile infantry does not occupy their firing positions in the trenches but remain in their dugouts, which are fully protected from all but the heaviest shells. Only a few observers are left in the trenches.
When the bombardment against this particular part of the line ceases the infantry leave their dugouts and man the firing positions. To prevent this is one of the most important as well as most difficult tasks of the artillery. This may be effected by a well-directed fire on the exits to the dugouts with a view to caving them in and thus preventing the egress of the occupants The enemy may sometimes be induced to leave his shelter prematurely by the following ruse:
1. Cease the artillery fire.
2. Open a heavy rifle fire; this causes the enemy to believe that the assault has begun and he will man his parapets in strength.
3. After waiting for several minutes open the artillery again with even increased vigor.
The hostile infantry may be forced out of his dugouts by the use of shells and grenades containing suffocating gases which penetrate the shelters and make them untenable.