Attack of Fortified Places. Including Siege-works, Mining, and Demolitions. / Prepared for the use of the Cadets of the United States Military Academy

by James Mercur

90. The Third Period of the Siege frequently called the “close attack,” includes all the steps between establishing the last parallel and the surrender of the place. These are the capture and crowning of the covered way, breaching the scarps and counter-scarps, passing the ditch, capturing and crowning the breaches of the outworks and main works in succession, and the final reduction of the interior retrenchments, or keep.

All these operations are carried on within close and deadly range of small arms and shells of Coehorn mortars, and many of them within range of hand grenades and upon ground honeycombed with mines and countermines, or liable to be flooded or inundated. They are slow in progress, uncertain in results, and require an extravagant expenditure of men and material. They can be pushed to a successful issue only when the artillery fire of the place is silenced and its small-arm fire is almost completely kept down by the fire of the attack.

The conditions of modern warfare are such, however, that by the time the attack has reached the foot of the glacis the losses and exhaustion of the garrison are frequently so great as to preclude an obstinate, close defence; and, in the majority of cases, the place is compelled to surrender before the close attack is commenced.

91. The capture and crowning of the covered way is accomplished by assault or by sap. The former is an extremely hazardous and bloody operation, which all authorities unite in condemning, and which should be undertaken only in extreme cases. It is carried out usually at night, by forming an assaulting party in the parallel, who rush forward to the crest of the covered way; capture, if possible, its guards, and under any attainable cover open a fire upon the crest of the work. All available small-arm and machine-gun fire combines with this to keep down the fire of the defence; and under cover of this fire the working parties construct, by flying sap, a trench crowning the covered way, and the communications between it and the parallel.

The trench is occupied as soon as it affords cover, and is subsequently completed and prepared for the reception of its guns and infantry guard.

In crowning the covered way by sap ([Pl. IV], Fig. 36), the saps are broken out from the parallel, a circular place of arms is constructed, which gives additional communication and serves as a depot for trench materials, the traversed sap is pushed forward, and the covered way crowned as previously described (par. 36). It will frequently be necessary to run out at right angles to this sap short branches of parallels ([Pl. IX], Fig. 83), to serve as places of arms, or as trenches of departure for mines or galleries, for underground warfare or for breaching walls.

92. Breaching the Scarps and Counter-scarps.—The counter-scarp, as a rule, and the scarp at times is breached by mining. (See Military Mining, pars. 91-93). When practicable, however, the scarp is breached with artillery and preferably by guns of the second artillery position; since a breaching battery on the crowning of the covered way, which must be provided with most ample splinter-proofs to protect the gunners from flying splinters of masonry and shot, is in general constructed only with great losses and delays; and the guns in this position must be fired under great angles of depression, requiring very deep embrasures to avoid exposing the cannoneers. When the ditch is deep and narrow it may be necessary to blow down the counter scarp and part of the glacis, in order to expose the scarp-wall to the fire of the breaching battery, whether on the glacis or at a distance. This necessity should be foreseen and provided for in locating the batteries.

A full or semi-detached scarp-wall will be breached when the battery is on the glacis by making vertical cuts at the ends, and a horizontal cut at about one third or one fourth its height from the bottom, and then firing shells into the part to be brought down, continuing the fire until the large masses of masonry are broken up, and the slope is made gentle and smooth enough to admit of easy ascent. A detached scarp-wall will be breached by a glacis battery, or any scarp-wall by a distant battery, by continued battering, which will not only knock down the wall, but also break up the fragments and make a practicable ramp.

93. The Capture and Crowning of the Breach.—The decision as to whether the breach shall be captured and crowned by assault or by sap will be governed by considerations similar to those which determined the character of the attack upon the covered way. The difficulties and dangers of the assault are perhaps greater than in that case. The assault, if undertaken, will be carried out in a similar manner, previous preparations having been made by making a practicable breach at least 25 to 30 yards wide, a practicable descent into the ditch of equal width, and a covered place of assembly for the working party and a depot of trench materials in immediate proximity to the breach.

The artillery defence of the ditch, whether from caponières, flank embrasures or casemates, or from adjacent works, must of course be silenced before crossing the ditch either by assault or by regular approach. This is accomplished by counter-batteries on the glacis, by heavy field guns located in temporary batteries in the trenches, by mines, or by overhead or indirect fire from the distant batteries, or from light mortars in the advanced trenches, as may be necessary.