An efficient outpost service must be maintained in front of these positions to prevent their being taken by surprise.
When but a limited number of troops are available for defence it is of course impossible to push out the advanced posts so far to the front. In all cases, however, they should be placed at the greatest practicable distance.
106. Opening of Artillery-fire by the Defence.—The artillery-fire of the defence should be opened upon the besieger’s batteries, etc., before they are ready for action, so that the ranges may be obtained and the tables of fire corrected without interference by the hostile fire. If this can be accomplished, the increased effect due to the accurate fire of the defence may more than counterbalance the numerical superiority of the attack, and result in preventing the completion of some of his batteries and in silencing others.
If, on the other hand, the attack anticipates the defence in obtaining the range, his superiority in numbers and accuracy will frequently necessitate abandoning some emplacements and mounting the guns in others, where they may be used in the later stages of the siege.
107. Defence during the Bombardment and Assault.—The amount of ammunition which can be profitably expended by the defence during the bombardment must be determined by the quantity on hand and the advisability of exposing by their fire the positions of the guns.
The infantry troops and the light guns are held under cover, ready to be moved forward to meet the assault if made. Special care will be taken to avoid being deceived by false attacks; and the assault, if made, will be met as previously described (par. 6).
If the attack is repulsed, an offensive return may be made by the general reserve, assisted, when necessary, by the local reserves of the front of attack; but the garrisons of the permanent works should not be withdrawn from them for this purpose, as it is always possible that they may be needed to protect the works and cover a retreat. If the assault succeeds, the defenders will retire to their positions in rear, from which the strongest possible fire will be directed upon the pursuing troops and upon the captured position to render its possession difficult or impossible. If the assailants are driven off, the position is immediately reoccupied by the defence.
108. Defence during the Second Period of the Siege.—The point of attack having been definitely determined by the preliminary steps of the attack in opening the parallels and establishing the batteries, the besieged will at once proceed to mount extra guns and reinforce the troops upon the threatened fronts. He will keep his outposts or sentinels during this and the subsequent periods as far to the front as possible, to prevent surprises and to keep out reconnoitring parties spies, etc., etc.
From observations previously established, he will locate at the earliest possible moment the batteries, etc., of the attack, and will prevent their completion and arming by the use of shells and case-shot charged with high explosives, fired from howitzers and mortars. He will use his long guns for counter-battering those of the besieger, and generally for direct fire upon exposed targets.
By taking the initiative he may frequently obtain the upper hand in the artillery duel, and possibly be able to prepare the way for strong sorties, and the destruction of the besieger’s works. In any case he must at this stage develop the full fire of his guns and work them to their maximum value.