[433]. True economy in expenditure of ammunition. When a certain fire effect is required, the necessary ammunition must be expended without hesitation. Several hours of firing may be necessary to gain fire superiority. True economy can be practiced only by closing on the enemy, as explained in [par. 344], before first opening fire, and thereafter suspending fire when there is nothing to shoot at. (419)
Supporting Artillery
[434]. Artillery fire principal aid of infantry. Artillery fire is the principal aid to the infantry in gaining and keeping fire superiority, not only by its hits, but by the moral effect it produces on the enemy. (420)
[435]. Functions of artillery fire in attack and defense. In attack, artillery assists the forward movement of the infantry. It keeps down the fire of the hostile artillery and seeks to neutralize the hostile infantry by inflicting losses upon it, destroying its morale, driving it to cover, and preventing it from using its weapons effectively.
In defense, it ignores the hostile artillery when the enemy's attack reaches a decisive stage and assists in checking the attack, joining its fire power to that of the defending infantry. (421)
[436]. Fire of artillery over friendly troops. Troops should be accustomed to being fired over by friendly artillery and impressed with the fact that the artillery should continue firing upon the enemy until the last possible moment. The few casualties resulting from shrapnel bursting short are trifling compared with those that would result from the increased effectiveness of the enemy's infantry fire were the friendly artillery to cease firing.
Casualties inflicted by supporting artillery are not probable until the opposing infantry lines are less than 200 yards apart. (422)
[437]. When no longer safe for artillery to fire over friendly troops. When the distance between the hostile infantry lines becomes so short as to render further use of friendly artillery inadvisable, the commander of the infantry firing line, using a preconcerted signal,[5] informs the artillery commander. The latter usually increases the range in order to impede the strengthening of the enemy's foremost line, as explained in [pars. 345]–346. (423)
Fire of Position
[438]. Fire of position, when used. Infantry is said to execute fire of position when it is posted so as to assist an attack by firing over the heads, or off the flank, of the attacking troops and is not itself to engage in the advance; or when, in defense, it is similarly posted to augment the fire of the main firing line.