The mines a, a, a, a, are constructed sufficiently low, while the others, b, b, b, are placed at half the height of the revetment. (See profile given in Plate V. fig. 6.) It is necessary, then, that the escarp gallery A (fig. 6), which represents the profile of the system, should be placed at such a level that it may not require too quick a descent in order to reach the mine B, placed at the foot of the breach, nor too rapid a rise to gain the mine C. If it be supposed, for example, that the height of the escarp is 30 feet, that the mine C is placed at half that height, that the mine B is 9 fee Plate V. below the bottom of the ditch, and that the escarp gallery is 20 yards from the back of the revetment, then the floor of the latter gallery ought to be raised about 6 feet above the bottom of the ditch, in order that the branches A B and A C may have slopes of equal inclination. Fig. 6 also shews the effects of the mines B and C on the ramp of the breach. A communication is sometimes established between the escarp and counterscarp galleries by means of a passage under the main ditch; but this sort of communication is not convenient, as it can only be entered either by a ladder or a quick ramp: moreover, it is liable to be filled with water, and made impassable. This arrangement has, however, some advantages, when there is a wish to dispute the descent into the ditch by mining operations; because the gallery in question forms a concealed and covered passage to the scene of the miner's operations. Without this under-ground gallery, it would be necessary, under such circumstances, to cross the main ditch, exposed and unprotected, in order to gain the counterscarp gallery; and as the besieger occupies the covered-way, this would be a service of great danger. It is, however, to be remarked, that the counterscarp gallery runs throughout the whole extent of the counterscarp, by which means it may be entered at distant points from the front of attack, which in this way may be reached; but besides, as this arrangement renders it necessary for the besieger to make a circuitous route, it is also necessary, in order to guard against surprise, to interrupt the communication, and to cut off the counterscarp gallery towards the flanks or extremities of the front of attack by strong barricades, in order to isolate the part of it attacked. Without such precaution, it might happen that a violent explosion disclosing an opening in the counterscarp gallery, the besieger might enter it in force, spread right and left, and menace with a surprise the different portions of the Body of the Place. Since, then, the counterscarp gallery does not always give to the besieged a sure route to reach the besieger's miner, when the latter is pushing his descent into the ditch, it is evident that there remains no other choice for the former than to cross the ditch, exposed to view from the besieger's lodgement, or else to employ the subterranean gallery already alluded to. When it is decided to construct such a communication, it is necessary to add a cesspool in the centre, and to arrange the floor of the gallery so as to drain into it the water that collects on its surface. In case the galleries of mines cannot be drained into the ditch of the main work, recourse must be had to similar cesspools. The dimensions of a gallery below the level of the ditch are the same as those of an ordinary gallery of communication, which is usually 6 feet high by 4 feet broad. But its masonry should be a little stronger than that of an ordinary gallery, because, having from its position but a slight covering of earth, it is liable to be crushed by Plate IV. shells: it is therefore usual to give it a thickness of about 2 feet. Fig. 5 shews that grooves are made in the masonry immediately behind the cesspool; by the assistance of which barricades could more easily be made in the gallery, which would intercept all communication when it is decided finally to abandon the mining operations under the covered-way. The names, dimensions, and positions of the various galleries having been now explained, it becomes necessary to describe the trace of a simple System of Defensive Mines, viz. that proposed by Dufour. (See Plates II. and III.) If the fortification have ravelins with considerable saliency, as in the French Modern Bastion System, it will be inexpedient to place mines under the glacis opposite the salients of the bastion. For it results from the march of the attack, that the besieger gains possession of the ravelin previous to pushing forward his approaches on the glacis opposite the bastion and therefore, as the passage of the main ditch is exposed to the view of the besieger's lodgements in the ravelin, the garrison could not communicate with the mines under the glacis of the bastion, excepting by a subterranean gallery below the ditch,—a mode which, as has been already stated, is often rendered impracticable from the difficulty of drainage, and is always insecure and uncertain. Besides, too, after the besieged have carried on for some time an active defensive subterranean warfare under the salient portions of their defences, it is not likely that the provision, either of powder or of men, would allow them to renew the struggle in the re-entering portions opposite the bastions. The system of defensive mines here proposed must, therefore, be considered as applied only to the salient portions of the trace: but it must be understood, that where the besieger could crown the covered-way of the ravelin and of the bastion at the same time, a similar disposition of defensive mines must continue along the whole contour of the glacis. Making the pan-coupé of the salient place of arms 9 yards in length, lines P q, qr, r 8, are drawn parallel to the crest of the glacis, and 60 yards from it. These ines give the limit of the extreme points of the galleries. Parallel to q r, and 72 yards from it, a gallery, tr, is made at right angles to the capital, and extending 20 yards on each side of it. Each end of this gallery is joined to the points q and r by two galleries, qt, rv, and the latter are produced to the counterscarp gallery. They are connected by a transverse gallery half-way between the lines qr, and t v, and parallel to them. A gallery on the capital extends from qr to the counterscarp gallery, and half-way between it and those terminating at q and r, are two others, extending only as far as the outer transverse one. The position of the galleries on each side is determined by placing the extreme points at equal distances of 26 yards apart, commencing from the points q and r. The first two are directed to the points t and r, and the remainder are parallel to them. In this system the chambers of the mines and the floors of the galleries are in two different planes, which intersect at the extremities of the galleries. The plane containPlate IV. ing the floors of the galleries, fig. 1, inclines towards the ditch, till it terminates in the counterscarp gallery: this inclination facilitates the drainage: the plane of the chambers of the mines inclines upwards, terminating at its intersection with a plane inclined to the horizon at an angle of 45°, and passing 8 yards from the crest of the glacis. The nearest mines to the fortress being at this intersection, will prevent the possibility of the besieged destroying the parapet of their own covered-way. The galleries are just near enough to insure the besieger's miner being heard, if he attempts to pass between them, but too far to ensure his being destroyed in them by the explosion of common mines. The position of the mine chambers is, therefore, reached by means of short branches, constructed for the purpose when the besieger's miner is heard at work. To facilitate this operation, openings a, a, a, a, fig. 1, large enough to commence branches from, are left in the revetment of the galleries, and parts even of the branches may be constructed permanently, in order to save time when the attack is made. At the junction of the galleries, the arrangements already described for increasing the ventilation and facilitating the communication would be made. PART V.-ATTACK AND DEFENCE OF A SYSTEM OF COUNTER SECTION I.-OPERATIONS OF THE BESIEGER WHEN HE ARRIVES IN THE VICINITY OF When the besieger arrives in the vicinity of the glacis of a countermined fortress, he is obliged to move more slowly, and dares not advance on the surface of the ground further than what he may be master of below. He then commences to excavate the earth, in order to try to discover the galleries of the besieged, and seize them, or To accomplish this, in the fig. 1, from 16 to 21 feet Plate VI. else he endeavours to blow them in by firing mines. middle of his third parallel he sinks shafts such as a, Often the besieged, especially when his galleries extend to a great distance, drives a branch almost under the third parallel, and fires one or more mines, such as c. The besieger under this supposition, ought to make a lodgement on the edge of the crater, as shewn in the figure, and sink a shaft (b) in his own lodgement. This shaft is not sunk from the bottom of the crater, because it would be the reservoir of all projectiles thrown from the place. Care must be taken, however, at the same time, to clear away the excavation caused by the globe of compression, in order to discover the direction of the branch which joins it, and which necessarily communicates with a main gallery. (See Plate VI.) While the besieger is sinking the shaft b, he ought frequently to listen, for there is not a doubt that he is now in the vicinity of the mines of the besieged; and when he arrives at the depth of 18 or 20 feet, he commences a branch e, breaking out on that side where he imagines the enemy's gallery to be situated. When the besieger finds himself sufficiently near to the Gallery of the Place, and is in danger of being forestalled, he hastens to dig a chamber at the extremity of his branch, in which he places a certain quantity of powder he then tamps as fast as possible, and endeavours to fire his mine before the besieged can find time to establish one to destroy his work. The besieged, on their side, directly they cease to hear the sound of the pickaxe, work with the greatest possible diligence, because they suppose from that instant their enemy is engaged in tamping their mine. If they have the good fortune to fall in with the mine, they endeavour to seize the powder, or else to saturate it by an inundation of water. If, on the contrary, they discover a part of the branch already excavated, they ought, without delay, to inundate it, in order to destroy the hose, and so prevent the powder from exploding. These artifices are made use of in like manner by the besieger. It sometimes happens that two miners, who are working to meet each other, are only separated by a slight partition of earth. This is an occasion seized upon to give the 'camouflet,' which is performed in this manner: the most active of the two pierces a hole on the side of his enemy with borers of different diameter, in order to enlarge it gradually, and to give it a diameter of 6 inches: he digs this hole as deep as he can, from 6 to 8 feet, for instance: he then introduces a large cartridge of the same size, containing from 12 to 20 lbs. of powder : he drives in this species of mine with a wooden plug, which he fixes and props up strongly with a piece of timber across the * Compiled by Lieut., now Captain, De Butts, R.E. branch finally, he fires this little mine by means of a fuze which goes through the middle of the plug. If the gallery of the enemy is but 4 or 5 feet from the head of this cartridge, he may be sure that it will be driven in by the explosion. To produce the same effect, two or three shells, fixed together, are sometimes employed; but this method requires a great deal of care and attention, in order that one's own labour be not exposed to destruction. In subterranean warfare, when two miners are working to meet each other, they take care to try the ground frequently with a borer, to find out exactly what distance they are off. In such a ease, he who sees the end of his enemy's borer appearing, keeps a strict watch on the moment it is drawn back: he then introduces quickly into the hole it leaves a pistol loaded with ball, and fires it the moment he imagines the hole is clear. This ought to be followed by three or four more; after which a probe is pushed into the opening, to clear it, and prevent the enemy from coming through on that side. Vauban recommends the following articles to be provided in attacks of this description: 1st. A frame of wood like a shield, 3" or 4" thick, with a bolt in the middle to manage it with, and to place it against the hole perforated by the probe. 2ndly. Smoke balls: they are pushed in through the same hole when lighted, and care is taken to stop the orifice on one's own side, so that all the smoke goes into the enemy's gallery, by which means their miner is driven away for some time. During his absence the mine is charged and fired, which, by blowing in the gallery, prevents the return of the enemy. If the opening is wide enough, a shell or portfires to suffocate, or grenades may be introduced. The shell is to be preferred when it can be used, because it destroys the part of the gallery where it falls. When a thin partition of earth divides the combatants, a petard is used to blow it in. Such are a great part of the artifices made use of by miners. To avoid them, the besieger should, as soon as he can, fire a mine to blow in the branches, and even the galleries of the besieged, if within reach. He is sure, by this means, of driving him away for some days. It is well known that the firing a mine shakes the ground to a considerable distance, so that if a gallery be within this limit, the gases of the powder penetrate and poison the air with such effect that no one can breathe it. This is not felt so much by the besieger, as he has more air, and is not obliged to use such long galleries. Notwithstanding all the obstacles opposed to the advance of a besieger, he finally contrives to discover one of the main galleries of the besieged. Sometimes he arrives at it direct by mining: sometimes he gains access by means of the branch of the enemy which he meets in his road. In both cases there are means of attacking and defending a gallery, which will be given in the following section. SECTION II.-STORMING OF THE GALLERIES-METHOD OF TURNING THE RETRENCHMENTS. As soon as the besieger has discovered the gallery of the enemy, he ought, without delay, to attack it with vigour. For this purpose he takes care to provide himself with a small rolling mantlet, or shield, 3' 2" broad, and three feet high at the most. If this machine were larger, it could not pass through the branches. Covered by this mantlet, the miner advances, followed by men armed with grenades, presenting towards the besieged a machine filled with pistol barrels, which keep up an incessant fire. He may also use grenades, or small shells, which are carried in a barrow, or other machine, behind which the miner covers himself. If by these different manœuvres he manages to penetrate to the retrenchments of the besieged, he endeavours to break it in, close with the enemy, and drive him back as far as possible by means of halberts, bayonets, and pistol-shots: after this, he barricades the abandoned gallery, or else makes a lodgement with sand-bags. The besieged, on their side, have different methods of intrenching themselves in their galleries. When they are in brick-work, care is taken to divide them beforePlate VI. hand, every 30 yards or so, by oak doors B and C (fig. 2). These doors are pierced with a large loophole, which is shut by a spring shutter. Inside and outside the door, blind branches (d,d) are made in the footings of the gallery, one to the right, the other on the left. The following is the object of this disposition. Let us suppose the gallery B C to be an envelope gallery into which the enemy have penetrated by the branch A. The defenders then retire behind the doors B and C, which are closed in such a manner that they can be barricaded on both sides: the spring shutter is opened, and through the loophole are thrown small leather sacks filled with fireworks, and lighted with a lighted piece of tow; grenades are also thrown into the abandoned part of the gallery. The burning and explosion of the powder enclosed in these different projectiles cause such a smoke that the besieger cannot support it. By repeating this manoeuvre, sufficient time is gained to bore, with a borer 6 or 7 inches in diameter, a hole in which from 24 to 30 lbs. of powder are placed, which is tamped properly. The explosion of these small mines (f, f,) will not fail to bring down the walls on the side of the besieger, and thus form in front of the gates a solid barrier, nearly inaccessible on account of the noxious vapours which generally exhale from earth and ruins impregnated with the smell of the powder. If the besieger observes that the gallery has a sensible slope towards one of the doors, towards B, for example, he ought to close it up with sand-bags, as shown at D, in order to prevent any return of hostilities from that side: then, taking advantage of the slope to B, he will roll down howitzer shells, which, bursting near the lower gate will break it in. The besieged is thus obliged to retire 30 yards further. If the slope were sufficient for a strong man to roll the shells right up to the next gate, the besieged might thus be forced to abandon 80 or 100 yards of gallery without risk to the besieger, and to which the besieged could not return if care were taken to burn at intervals bags of powder. It may, however, happen that the besieged are so strongly retrenched, and have so well known how to employ their means of defence, that the besieger is obliged to give Plate VI. fig. 2. up the hope of penetrating by the branch A. In this case a great deal of confusion may be caused in the enemy's gallery, and all the barricades broken down by rolling against them one or two barrels of powder, having a lighted match attached. But if B C form part of an envelope, or of any other gallery of great length, and in a straight line, there is another mode of attacking and turning the retrenchments, both easy and expeditious; and which may be thus explained. The besieging miner closes instantly the opening G with sand-bags, which he makes secure by filling up the spaces between the bags with clay, well rammed in. This done, he works without ceasing at the excavation of branches, 5 or 6 yards long, by the side of the foundations of the gallery. At the extremities, holes are driven with a borer from the top of the branches to the surface of the ground. The ends of the borer shew on the surface (of the ground) two points which will be of service in discovering the direction of the long gallery. Let us suppose that by this means the position of the gallery A B (fig. 3) has been discovered a flying sap is thrown up as far as B the following night, above |