If, however, the superiority of the artillery of the attack is pronounced, and it becomes impracticable to serve any battery advantageously, it will be better to dismount its guns and remount them in other positions, as indicated in the preceding paragraph (par. 106).
All efforts will be made to prevent the construction of the parallels and approaches, their positions being discovered by the use of the search and other lights, and the work upon them retarded by direct and curved fire. For the latter light rifled mortars promise to be very effective.[7]
The trenches connecting the detached and intermediate works will be strengthened, and counter-approaches will when practicable be driven out to afford positions for enfilading the approaches. The field and machine guns will be held in constant readiness for use, and will be brought into action at every favorable opportunity; but will be withdrawn and placed under cover previously prepared so soon as the fire upon them becomes too severe to be endured.
Meanwhile a new position in rear, with its flanks supported upon the adjacent detached works, will be selected and made ready for defence in case the front line is taken.
The general reserve will be used for offensive movements, which are made whenever favorable opportunities arise, particularly in making counter-attacks after unsuccessful assaults.
109. Defence during the Third Period.—The defence of the detached works of an intrenched camp during the Third Period will be conducted, so far as the general reserve is concerned, in very much the same manner as during the Second Period; but in the immediate defence of the detached work itself, owing to the close approach of the besieger, its character will change. The artillery except the field and machine guns will be silenced, and the latter will usually be only available for defending the ditches and for repelling assaults. Light guns will, however, be held in readiness for temporary use when practicable.
The outposts will of necessity be drawn in and replaced by a chain of sentinels along the parapets of the covered way or the main parapet, who will pick off the besiegers at every possible chance, and will be reinforced by the rest of the garrison when an assault is imminent. All flanking defences will be kept in as good condition as possible, and in readiness to prevent the crossing of the ditch, or to repulse an assault. Grenades and shells will be kept in readiness to roll into the ditch, the breaches will be obstructed and mined if practicable, counter-mines will be brought into play, and all other possible measures taken to retard the approach of the besieger to the breach and to repel his assaults. When, however, the work is reduced to such a state as to make its defence hopeless, it should not be held at the expense of great losses to the defence, unless the besieger’s works can be considerably delayed by doing so. When the position consists of an enceinte with ordinary outworks, the investment during the Third Period of the siege will be closer, the opportunities for using the general reserve will usually disappear, and its troops will be merged with those of the general defence.
When, in this case, the place is to be defended to the last, all measures will be taken for the defence of the breach; and after this is carried, for the final defence of the inner retrenchments or keeps.
The tactical handling of the garrison for this purpose is in accordance with the principles already laid down (par. 6, and Art of War, pars. 282-84.)
The sorties recommended during a siege are, when made by the general reserve and in large bodies, usually carried out by moving the troops from the collateral works upon the flanks of the besieger’s works. In the close attack, however, they may be made by small parties moving to the front from the nearest outpost or salient. The object in all cases is the same—to destroy the enemy’s works, delay his advance, and inflict upon him all possible loss.