The same considerations govern the construction and armament of batteries designed to destroy réduits, barracks, gorge walls, city gates, magazines, depots, bridges, locks, etc., etc.
85.Batteries of rifled mortars or of howitzers for vertical fireshould be so located, when possible, that the longest dimension of the target will be in the direction of their fire. The effect of their projectiles is greatest when they can be fired at elevations, of 60° to 70° and with large charges. These considerations, combined with those of good cover and easy supply, will govern their location.
86.Opening and conduct of fire from Second Artillery position.—The batteries which are ready on the morning of the completion of the parallel open fire simultaneously upon the work, and are supported by those of the first artillery position still armed. Thesame rules govern the fire of the first and of the second artillery position.
When the defence combines a number of batteries to silence one of the attack a heavy fire is concentrated upon these batteries by those from which the fire has been diverted. New batteries unmasked by the defence, or established in intermediate or other works, should receive prompt attention from the attack, with a view to silencing them if possible before they correct their ranges. It is of the first importance that the superiority of the artillery fire of the attack shall be established at the opening of fire from the first artillery position and be maintained throughout, and that the defence shall be prevented from repairing any batteries which have been silenced. To this end a few guns will keep up a slow fire upon these batteries so long as it may be necessary.
Every gun of the defence must, if possible, be kept under a heavy fire, and the fire upon the enceinte must be opened at the earliest possible date and continued day and night, as previously described.
87.Musketry firewill be opened as soon as a parallel is established at such distance as to make it effective; and this may be, for a well-regulated fire of sharpshooters, at ranges of 1200 to 1500 yards, or in some cases even greater.
88.The Advance from the First Parallel.—It is assumed that the fire from the first and second artillery positions will silence almost completely the artillery fire of the work upon the fronts attacked; but the defence will still be able to develop when necessary a strong musketry fire, aided at times by machine and rapid-fire or even some field guns. Consequently, the advance from the parallel must be under cover.
Approaches are, therefore, broken out from the parallel and pushed forward towards the work, the workmen being protected by the fire of the guards of the trenches. Usually at least three lines of approaches are constructed, concentrating upon the point of attack and following generally the lines of the capitals of the adjacent salients.
When attacking a line of detached works two or more lines of approaches may be constructed towards each work attacked. The approaches are run in zigzags, each branch so directed as to pass a short distance (30 or 40 yards) outside the most advanced work of the defence from which it could be enfiladed; at each change of direction of the zigzags a return of 10 or 20 yards is made to cover the approach in rear (Pl. VIII, Figs. 80 and 81). The length of the branches is so regulated as not to mask too much of the front of the parallel; they consequently grow shorter as they approach the work and vary ordinarily between 200 and 50 yards, seldom exceeding 100 yards when near the work. The heads of the different approaches are advanced at about equal speed so as to afford mutual support.
89.The Second Parallel.—The second parallel is located nearer to the first parallel than to the covered way, sometimes very much nearer. It is constructed and occupied by the guard of the trenches. The principle followed is that the guards of the trenches shall always be nearer to the head of the sap than is the enemy in his most advanced place of arms; so that, in case of a sortie, the advantage will lie with the besieger. The flanks of the second parallel are refused and strengthened like those of the first, or are even carried back to the first parallel, to guard them against flank attacks.
The second parallel having been completed and occupied, serves as a base for further advance, which is conducted according to the same methods, “demi-parallels” (Pl. VIII, Fig. 81) being run out to the right and left of the approaches when they are well advanced beyond the second parallel. These demi-parallels are sometimes joined, forming a third parallel, from which the approaches are advanced as before, with additional parallels when needed, until the foot of the glacis or exterior of the counter-mines is reached. The number of parallels is determined by the distance at which the first is established and the vigor of the defence; formerly three were considered all that were needed, and this number was used at Strasburg, 1870. At other modern sieges a larger number has frequently been required. At Belfort (1870-71) the third parallel was established at 1200 yards from the place. Five parallels were used at the siege of Fort Wagner (July-September, 1863).
The approaches are driven in zigzags by simple trench, flying or full sap, until the direct advance becomes equal to about one third of the length of trench; and from this point they are driven directly upon the work by double-traversed sap (Pl. III, Figs. 28-35), the latter being, as a rule, used only in advancing from the foot of the glacis, or during the third period of the siege.
90.The Third Period of the Siegefrequently 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 andcounter-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 wayis accomplished byassaultor bysap. 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 thedefence; 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 orderto 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 byassaultor bysapwill 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. Theassault, 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.
If the interior arrangement of the work is known by the besieger the assault maybe made by night; but if it is unknown, the confusion resulting from a night attack will be so great as to render its success almost hopeless, and the assault will have to be delivered by day.
The assaulting columns will be made up of an advanced line of skirmishers (selected men, good shots, and generally volunteers), followed by a working party of sappers to clear away obstacles, these closely followed by the columns of assault; while the supports and reserves move forward in the trenches to join in the assault as circumstances require. The troops who first gain the crest establish themselves there and hold the breach until those coming after them pass and engage the garrison, while some detachments strive to capture and open one gate or more to admit the reserves. The assaulting force should be equal at least to once and a half or twice the garrison, and simultaneous attacks should be made upon other breaches or accessible parts of the work to divide the attention of the defence.
These false attacks are sometimes successful, and preparations for taking advantage of this contingency should not be omitted. The subdivisions of the assaulting force should each receive explicit instructions as to its special object, and under no circumstances should their lines of march intersect. Unmistakable signals of recognition should be prescribed to prevent conflicts arising between the different parties meetingwithin the work. The bombardment preceding the attack should not cease, and thus notify the defence when the assault is to be made; but the guns should be directed upon adjacent parts of the work until the assault penetrates the work or is repulsed.
94.In theattack by the sapthe method of crossing the ditch adapted to the circumstances is used (pars. 39-41,Pl. IV, Figs. 37-41) and the sap is started at the foot of the breach, driven up it, and the breach is crowned according to the methods previously described (par. 36).
The sappers are protected from small sorties by the fire from the crowning of the covered way and any other points bearing on the head of the sap. Fireballs, electric lights and other means will be used during the night to light up the parapets of the work and expose the defenders, in this as in the previous operations of the siege. The crowning of the breach will be extended and converted into a place of arms, from which further sapping can be carried on in a similar manner, until the breach in the last retrenchment is crowned and the preparations for the final attack upon the garrison are made, or the place surrenders. If the garrison takes refuge in an interior keep and continues the defence the keep must be reduced by similar methods.
95.Additional Operations in the Attack of an Intrenched Camp.—The operations above described are those necessary to reduce a fortified place of the older type, or a detached work of an intrenched camp. The latter, though of less extent and with a smaller garrison, offers as a rule greater resisting power, since it is usually subject to front fire only, has more completebomb-proof cover, and is free from the presence of non-combatants.
While a great advantage is gained by the capture of two or more of the advanced forts, the resisting power of the intrenched camp is by no means destroyed. These forts are subject to the fire of the collateral works, of which frequently two or more must be silenced before a further advance can be made. The beleaguered army may still be in condition to recapture the forts by vigorous assaults; and in almost every case, before the fall of the works of the outer line, a line of provisional fortifications of high resisting power, connected by trenches, will have been constructed by the defence in rear of the captured works, with its flanks secured by the collateral works of the outer line. An assault against works of this class offers no prospect of success. The besieger is therefore obliged, as soon as he captures a detached fort, to put it in condition to withstand the assaults of the besieged army and to afford protection from the artillery fire of the collateral works, and then to push forward his approaches against the successive positions prepared by the defence, which will as a rule present a front equal to or greater than that which can be occupied by the attack. The gorges of the captured works are repaired and strengthened, covered communications are made through the faces, either through the breaches or in more convenient points, traverses are repaired or built to protect against the fire of the collateral works, and the captured works are connected by trenches which afford emplacements for batteries and form a new parallel from which the saps can be driven in attacking the intermediate works. Simultaneously withthis attack, it is usually advisable to advance from the flanks of the first or second parallel upon the forts of the outer line which form the flanks of the intermediate line. The approaches can generally be driven with comparative ease owing to these works having already been partly disabled and now being subject to a flank and reverse fire from the newly-established batteries.
The flanks of the intermediate line being turned by the capture of these works, a portion or the whole of it will of necessity be abandoned. The subsequent operations up to the capture of the enceinte will be of the same nature as those already described.
96.Occupation of a Conquered Place.—Immediately upon the fall of the place it must be occupied by a force (chosen when possible from the reserve which has not participated in the final assault) sufficient to control not only the inhabitants, but also the disorderly soldiers of the attacking force. All pillaging, wanton destruction, and abuse of the conquered must be restrained with a strong hand, immediate and exemplary punishment being inflicted upon offenders. The orderly portion of the defenders must be protected, and such steps taken for supplying their needs as humanity requires; while the disorderly ones must be repressed with such severity as may be necessary. So soon as order is established a careful inventory of captured property is made, and it is stored subject to the orders of the government. When the possibility exists of the place being attacked or besieged by the enemy, all its resources which are available for defence are collected, repaired, and stored for use.
97.Marshal Vauban, the great French military engineer (born 1633, died 1707), whose experience and success in sieges made him the great authority on the subject, formulated certain maxims for governing the conduct of a siege, the observance of which led to almost certain success, and the departure from them almost invariably resulted disastrously. The most of these are as applicable to sieges of to-day as they were to those of his own time. The following6bear upon the second and third periods of the attack:
1st. To delay the opening of the trenches until the besieging forces are all well posted and made secure by fortifications from an attack either from the garrison or from a succoring force; and until everything requisite for carrying on the work vigorously has been collected and is ready at hand when wanted.
2d. To make a single attack rather than a double one, unless the two attacks can be well connected and the besieging force exceeds considerably in strength the garrison. This, as a matter of course, excludes false attacks, and double separate attacks, unless the superiority of the besieging force is very great. By a single attack is understood one by which it is proposed to gain possession of the main work by a single breach at some point; by a double attack it is proposed to effect two breaches of the main work. The advantage of the latter lies in forcing the garrison to divide their strength for the defence of the two breaches, whilst the assailing forces, being under one leadership, can at anymoment concentrate if necessary upon the point most favorable to their assault.
3d. To embrace within the parallels and approaches all the defences which bear upon the site to be occupied by the besieger’s works, in order to have secure positions for establishing the batteries that may be required to silence the fire of these defences.
4th. To multiply the approaches, with the view of giving mutual support, less encumbered communications, and dividing the fire of the defences, which, if concentrated upon a single one, might soon destroy it.
5th. To throw up at least three main lines of parallels, placing them in the best positions for mutual support and for guarding the approaches and batteries from sorties of the besieged.
6th. To avoid attacking a point upon which the approaches can be run only on a narrow front, or one which can only be approached over marshy ground, or on causeways.
7th. To be careful not to push forward any portion of the trenches until they are well flanked and protected by trenches in their rear, which are completed and occupied by troops.
8th. To avoid encumbering the approaches with trench materials, tools, workmen, or troops; placing all of these in the parallels, on the right and left of the approaches, so as to be ready at hand when wanted, and to be rapidly sent forward through the trenches of the approaches, which should be kept free for this purpose.
9th. To place the ricochet (enfilading) batteries in such positions that they can have an enfilading and slant reverse fire upon the guns of the defences to be attained by them.
10th. To refrain from opening fire from any series of batteries until it can be done at the same moment from all of them.
[In connection with this and other siege operations, Vauban remarks that precipitation in sieges does not hasten the close of them, but often prolongs them and renders them more bloody.]
11th. To employ the fire of the batteries and trenches, rather than open assaults, to drive the besieged from their defences, before attempting to occupy them by the besieging force.
12th. When it is decided to make an open assault, to do so by day, if there is no portion of the fire of the defences which bears upon the point to be carried that is not completely kept under by the fire of the batteries and trenches; but, in the contrary case, when the fire of the defences is not completely kept under, to make a night assault.
13th. Not to attempt an obstinate resistance to an open assault of the besieged upon any unfinished portion of the trenches; but rather to withdraw the workmen and the few troops near them to some point behind the parallel immediately in rear, and then to open a vigorous fire from it upon the assailing force.
14th. To keep within the cover of the parallel when the assailant is advancing to the assault, and leave him to expose himself to its fire as long as he pleases, and then, when he is well cut up, and has got thrown into confusion, as he necessarily will at night, in the trenches that he may have carried, to fall upon him with the bayonet and drive him out.
15th. Not to push such charges too far from the parallel, but to retire promptly, so soon as the assailanthas fairly taken to flight, within the cover of the parallel, so as not to draw the fire of the besieged works.
98.In connection with the plan of attack previously referred to (par. 78), a completeJournal of the Attackwill be kept in which will be recorded day by day a detailed record of the daily progress of the siege, giving the day and hour of starting and completing each battery, parallel, approach, etc., with their daily progress, dates of opening fire from each battery, and, generally, every incident connected with the siege. This journal will be supplemented by journals kept by the chiefs of engineers and artillery, in which will be consolidated the daily reports of all subordinate commanders of these respective arms, giving the expenditure of ammunition, the performance of the guns, carriages, etc.; the modification made in details of parapets, batteries, magazines, etc., with their value; the results of trials of new devices, and special reports upon any points connected with the siege. These journals will be carefully preserved and copies transmitted to the War Department from time to time for future use.
99.Preliminary Considerations.—The defence of a fortified place is entrusted to a commanding officer, who, when the siege is established, is generally known as the “Governor of the Place.” His duties become more exacting and his powers more absolute from the beginning of hostilities until the place is invested and cut off from communication with the exterior, when, since the whole responsibility of the defence rests upon him, his powers over both the garrison and the inhabitants of the place, of necessity become autocratic in all matters affecting the defence, directly or indirectly. He, of course, avails himself of the counsel and advice of his subordinate officers and may make up a “Council of Defence” from his second in command and the commander of the engineers and of the artillery; but the ultimate decision of all questions must rest with him alone.
During peace and after the beginning of hostilities up to the near approach of the investing force, the civil authorities retain their ordinary jurisdiction, unless martial law is declared by proper authority; but after the place is invested, martial law (or state of siege) exists from necessity, and the police power, the control of provisions and supplies of all kinds, public and private, buildings, animals, vehicles, etc., and everything necessary for the defence of the place fall into thehands of the governor, who also is empowered to direct who shall be sent out and who shall be retained within the place, and what necessary service or labor shall be performed by the inhabitants. Having been selected for these onerous and exacting duties, he, under no circumstances, allows himself to be cut off from his post, and is therefore debarred from leading his troops in person in the active operations outside the work or exposing himself unnecessarily or recklessly during any period of the siege.
100.The Garrison.—The garrison should consist of artillery and infantry, and, in an intrenched camp, of enough mounted troops for escort, messenger, and a limited vedette service.
The strength of the infantry is generally regulated so as to give a suitable garrison to each detached work, and about 1½ to 2 men for each yard of the front of attack. The artillery is allowed about 12 men for each gun. The number of engineers is determined for each place by the probable amount of engineer work that will be required. These troops make up about one-third of the entire force.
A general reserve of all arms (principally, however, foot troops) makes up the other two-thirds, and is held as “a fighting force” for preventing the investment of the place, or for breaking up the investing lines when established. This reserve is called upon for work on the front of attack or in the trenches only when it cannot be avoided.
In smaller places the portion of the garrison called upon for the outer line of defence may be increased to one-half or two-thirds, and the general reserve be reduced to one-half or one-third of the entire force.When the investment is strongly established the general reserve will usually be combined with the other troops.
The troops engaged on the front of attack are usually assigned to the different sectors of attack and are divided into reliefs (ordinarily three), each relief having as a rule a tour of one day in the front lines, one in the immediate supports, and one in the reserve and in interior fatigue duty. The Governor, however, so regulates the details as to impose upon the troops the least work consistent with an energetic defence.
101.Armament.—The guns for arming the place should be placed in position or in store within the works before the beginning of hostilities. There should be mounted in commanding positions a sufficient number of high-power guns to hold the enemy’s first works at a distance and to fire upon his camps, etc., if placed too near. In addition to these, a full supply of light guns, including machine and rapid-fire guns, should be at all times equipped and supplied for immediate use in meeting an assault or surprise. Their emplacements, platforms, etc., should be in readiness for use at any moment.
In large places and for an active defence there will be needed also enough field-guns to properly equip the general reserve (about 4 guns per 1000 men). These should be considered a part of the equipment of the reserve.
It being, from economical considerations, impossible to supply guns to fully arm all the fronts of a place, enough only are usually provided to thoroughly equip the sector of attack and to replace those disabled. These are stored within the place where they are secure against deterioration or injury, and are mountedin the sector of attack when it is definitely determined. The numbers of high-powered guns, howitzers, mortars, and machine and rapid-fire guns needed must be determined from the size of the place, its garrison, and the character of attack which may be expected.
102.Ammunition, Provisions and Supplies.—A plentiful supply of ammunition, especially of projectiles, for all the guns should be kept constantly on hand. The projectiles, which may be stored for an indefinite term without deterioration, may be distributed in magazines in proximity to their batteries; the powder should be so stored as to preserve its properties, and be distributed to the service magazines at such times and in such quantities as may be necessary. Other equipments will be stored and handled in accordance with the same principles.
The utmost care will be taken in storing and issuing the provisions and supplies belonging to the troops; and in cases of necessity during the siege the sales of provisions to the inhabitants by the dealers will be regulated, both in prices and quantities, by the military governor.
103.Sanitation and Hygiene.—The most rigid sanitary measures and rules of hygiene should be enforced from the beginning of the siege, under the direction of the military governor, whose medical officers should join with the health officers of the place (if any exist) in guarding not only the troops but all the inhabitants from all avoidable causes of epidemic diseases. Extreme rigor in carrying out these regulations in not only allowable, but is most urgently required.
104.Preparations for Defence.—An active defencebeing presupposed, all possible measures for its execution should be taken before the near approach of the enemy interferes with them. The principal ones are as follows, viz.: Advanced posts are established as far from the work as is prudent, say 3500 to 4000 yards, placed at points which may be easily defended or which would be advantageous positions for the enemy’s batteries, etc. These, when possible, should be so placed that the ground between them is swept by their infantry fire and by the artillery of the place. They should be provided with good cover for the troops, and parapets for infantry and field-guns. When not naturally strong, field-works should be built. Quarries, ditches, sunken roads, villages, woods, etc., should be taken advantage of, either as points of defence, passive obstacles, or covers for communications, as may be best. Lines of retreat to the work as secure as possible from hostile fire should be provided. All supplies in the vicinity of the work which will be useful during the siege should be collected and taken into the place. Means of communicating with the exterior by telegraph, telephone, signal flags, lanterns and heliotropes, carrier-pigeons and balloons, should be secured. Search-lights for illuminating the exterior should be obtained, and as soon as practicable bomb-proofs and shelters for the inhabitants should be prepared in the body of the place; and in connection with the civil authorities the fire department of the place should be organized and taught how to extinguish fires with dry earth and by pulling down buildings when water is not available.
The service of security and information should be extended to the furthest possible limit, not only byoutposts, etc., but by telegraph operators and reliable correspondents at long distances from the place; and preparations should be made to retard the approach of the enemy by the destruction of the roads, bridges, etc.
105.Defence during the First Period of the Siege.—Upon the approach of the enemy each work should receive its permanent garrison, and the fighting reserve should go out to occupy the advanced posts and to take full advantage of its interior lines to hold him back and punish any careless or ill-advised advance, being aided in this when possible by the fire of the heavy guns of the place. Care must be taken to avoid too great dispersion of the troops, and exposing advanced parties to being cut off and captured by pushing them too far to the front or holding their positions too long; but no opportunity should be missed of attacking and destroying or beating back hostile detachments when tactical conditions warrant it.
The defence during the first part of this period differs but little from the ordinary defence of an intrenched battle-field. The principal differences arise from the fact that the flanks of the advanced lines and the lines of retreat to the work are so well covered that with ordinary precautions they may be considered secure, and all energies may be directed to meeting the front attack and executing offensive returns. So soon as the point of attack selected by the enemy becomes known the advanced positions may be more fully manned and equipped; trenches with inconspicuous parapets, or preferably without any, may be made to cover the infantry, field-guns, and sometimes siege-guns on travelling carriages. These positions may be, as previously stated, 2500 to 3000 yards from the permanentworks, and the intervals between them may be swept by the heavy guns of the latter.
If these positions can be so strongly held as to compel the besieger to attack them with his heavy guns, he will be compelled to establish his first artillery position at a very great distance—possibly 5000 to 6000 yards from the work. [At Belfort, 1870, positions of this kind were taken only after seventy-seven days of siege.]
As the advanced positions may be subject to the fire of the heaviest class of siege-guns, if any parapet is made it should be of the nature of a glacis of gentle slope and little command. Infantry trenches should be made narrow and deep as a protection against shells and shrapnel (Pl. IX, Fig. 84), and gun-emplacements should be as small as practicable and almost entirely in excavation, for the same reason. Positions so prepared suffer very little from gun-fire, and will frequently require attack by systematic approaches.
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 defencemay 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.
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 curvedfire. 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 repellingassaults. 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, whenmade 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.
110.Should the defensive policy of the state not require a place to be held to extremity, the governor must be fully informed of the fact, and the extent of the defence and the conditions of capitulation must be fully understood by him before the investment. As a rule, however, no excuse will be received for the surrender of a place until every means of defence is exhausted, and further resistance is not only hopeless, but impossible, the only rule which can guide the governor being that “one additional day of defence may be of incalculable benefit to his country.” The old rule, copied from the French, but no longer observed by them, requires the defence to sustain at least one assault on a practicable breach in the body of the place.
Within recent years, in civilized warfare, no cases have occurred in which such assaults have been made, the places having been reduced by the more distant attack; but assuming such an assault to be repulsed, it will not justify the surrender of the place so long as a possibility of repulsing similar assaults exists. The garrison must withstand all attacks of whatever nature to the last extremity, and continue the defence up tothe full requirements of duty and honor—surrendering only when nothing else is possible.
111.A Journal of the Defence, entirely similar to that of the attack, will be kept by the besieged for use by the War Department in case of a successful defence. Nothing should be entered in the journal which might be of special value to the besieger in case the place is taken, but a separate journal of such matter should be kept in cipher, or should be destroyed before the surrender of the place.
112.The Engineer and Artillery Parks and Depotsare located and arranged for security against the artillery-fire and the attack, by surprise or otherwise, of the defence, and also for facility in receiving, storing, and distributing materials and supplies.
The first condition is fulfilled by placing them at a safe distance, concealing them from the view of the defence if possible, and guarding them against attack, and the access of incendiaries, etc., by strict application of ordinary defensive tactics, and a most thorough system of interior guards. Powder depots, trains, etc., especially are guarded against the access of all unauthorized persons.
The second condition, when railroad communication is used, is satisfied by making the park conform to the best-planned railroad terminals and freight-yards. A type arrangement is given in Plate IX, Fig. 85, in which switches from the main line give access to as many side-tracks,a,b,c,d, etc., and spurs, 1, 2, 3, etc., as may be needed. When practicable, these sidings should connect at each end with the main line in order to afford free ingress and egress from both directions. They should be placed at such distances apart as toallow loading-platforms and the desired room for sheds, piles of materials, etc., between them; large areas being left for light, and small for heavy, materials. The spurs, 1, 2, 3, etc., should preferably be short; but if long, should be connected by switches. AY, as indicated, is frequently convenient for reversing complete trains without uncoupling the cars, and is indispensable when a turn-table is not available.
When the powder-depot is separated from the main park it is better to reach it by a special track branching from the main line at some distance from the park, so that the ammunition-trains will not pass through or near the latter. The sketch given is proposed as a type only, since the park may occupy one or both sides of the main line, be long and narrow, short and broad, regular or irregular in outline, as may best conform to the ground available.
Standard-gauge roads will, when practicable, be laid between the main park and the smaller depots. When this is not feasible, narrow-gauge tram-roads will be used instead, and will also connect the smaller depots with the trenches and batteries. The portable tramways used by contractors are well fitted for use in the trenches.
When the park is located upon navigable water a number of piers and wharves are occupied. They should be provided with derricks or cranes, and tracks and cars upon which materials may be loaded directly from the ships. The park may then be arranged on the general plan above indicated. The switches are so arranged as to allow empty cars to return to the wharves on a track different from that used by the loaded ones.
In storing materials and supplies in the park care must be taken to place each class by itself, and to so pile them that they can be readily inventoried and inspected, and be removed or replaced without disturbing other piles. This requires the piles to be arranged in regular order, with unobstructed passages between them, and prohibits piling articles of different kinds or sizes on top of each other.
113.In a regular siege, the besieging army will, as a regular rule, eventually be provided with tents or portable huts for shelter; but before this is accomplished much suffering and consequent disease may result from exposure, which could be avoided by the construction of temporary shelters, huts, and screens from materials available for this purpose.
In severe winter weather tents and thin wooden huts do not afford sufficient protection, and it may be necessary to substitute for them others with walls of logs, sods, sand-bags, adobe, or other materials, or even huts partly or entirely sunk into the earth. The greatest care must be exercised in enforcing proper ventilation and cleanliness in huts of this class. If this is not done serious fevers and other camp diseases are almost sure to occur. (Art of War, Art. 352-3.) The figures given (Plate IX, Figs. 86-94) have been selected from a great many examples to serve as suggestions. They may be modified or combined, as circumstances require. Their construction is evident from the figures, and requires no description. Ditches surrounding the huts are made to carry off rain-water.Heavy roofs are supported by poles set up inside the hut as needed. Fireplaces are dug in the sides of the excavation, or are built up of sods, clay, etc. It is better to make two, as shown, to obtain a good draught in any wind. Chimneys are made of sods or of sticks plastered with clay, unless drain-tiles, tin cans, or other suitable materials can be found. Great care must be taken to prevent their setting the roof on fire.
In many cases water-proof roofing felts and papers may be obtained and used for roofs, etc., in huts and shelters. The lumber from packing-boxes, tin from canned vegetables, and wire from baled forage may frequently be utilized for doors, chimneys, ties, etc. Straw mats for mattresses, etc., are economical in the use of straw and conduce to cleanliness, as they can be easily taken up and replaced. The method of making them is shown inPl. IX, Fig. 95. When twine is not at hand, they may be woven of straw rope. They, as well as all other bedding, should be taken out and sunned every dry day. Ordinary hurdles laid upon the ground or raised a few inches above it protect the blankets, etc., from the moisture of the earth.
It cannot be too strongly impressed upon officers, that all devices of the kind above indicated, which add to the comfort of the men, add also to their health, morale, and efficiency.
114.In our service a company will usually have a camp-cooking outfit sufficient for its needs, and generally of good pattern; but these are not always on hand when needed, and small detachments are frequentlydeprived of them for days or weeks. In ordinary soil, kitchens, and in a clay soil ovens, can be constructed, which, with a few kettles and cans, will enable the men to prepare for themselves fairly good meals without unnecessary waste of fuel. A few of these are figured in Pls. IX, X, Figs. 96-103. The banks of the trench shown in Fig. 96 afford support for cross-bars, and protect the fire from the wind. The type shown in Figs. 97, 102, 103 take the place of a stove, require but little fuel, and secure a steady heat. To obtain a good draught they should be so built that the wind blows toward the chimney. For this purpose they may radiate from a central chimney. (The flues of those not in use may be temporarily stopped up with sods.) The arch of the oven shown inPl. X, Fgs. 98-101, may be built over a piece of sheet iron if it can be obtained; if not, over a hurdle well smeared with clay. A slow fire will, under favorable conditions, dry and bake the clay arch so that it will stand after the brushwood of the hurdle is burned out. They may then be heated and used for baking.
115.Latrines and sinks for the reception of garbage, etc., are objects of the greatest importance in all camps, temporary or permanent; and, unless properly made and cared for, they speedily make their presence known, and become a most prolific source of discomfort and disease.
For permanent camps liable to be occupied for a long time special arrangements for the disinfection, removal, and destruction of garbage and excreta must be made. For temporary camps it will suffice to providepits with suitable conveniences and screens; covering with a thin layer of the excavated earth all deposited garbage and excreta before they become offensive. When, as is sometimes the case, these pits cannot be kept free from water, it may be necessary to use in addition lime, copperas, carbolic acid, or other chemical disinfectants and deodorizers.
The ordinary constructions used in temporary camps are shown inPl. X, Figs. 104-107. Separate latrines for officers are constructed and screened. The seat shown in Fig. 107, when one can be obtained, adds much to their comfort.
In more permanent camps the latrines may be roofed and screened with canvas or boards, and board seats be provided for the men. Uninclosed sinks and latrines should have earthen banks all around them, to indicate their position and to prevent men walking into them at night. Upon abandoning a camp all sinks and latrines are to be disinfected and filled up.
116.The problem of obtaining a sufficient and wholesome water-supply for a besieging army is usually one difficult of solution. The precautions which are necessary in ordinary camps (Art. of War, 352 and 358) become of still greater importance in this case, owing to the choice of the source of supply being limited to those which are not controlled by the besieged, and to the constantly increasing danger of pollution of all ground waters by the bodies of the dead men and animals and the refuse and filth of the camps. The evils arising from these sources may be largely or entirelyremoved by boiling the drinking-water, and the disagreeable tastes and smells may be removed by filtering through good filters. It is very difficult, however, to compel the men to boil the water, or to drink it after it is boiled, unless it is properly aerated and filtered. All available measures should, therefore, be adopted to supply them with wholesome water.
The results of the most recent researches show that properly conductedintermittent filtrationwith sand-filters will render a polluted water almost if not entirely safe. (See reports of Massachusetts State Board of Health on Purification of Sewage and Water, 1890.) And the analysis of water sterilized by a steam-jet at the Columbian Exposition in Chicago, 1893, gives reason to believe that this process may be very effective in removing disease germs. (See report of Allen Hazen, Chemist, Department of Water-supply, published inEngineering News, March 29, 1894.) In camps of some permanence one or both of these processes may be well worth applying.
Small filters for limited amounts of water may be bought in the market, or may be improvised and set up for officers or company messes. Figs. 108-110,Pl. X, are given as suggestions; they serve as strainers in any case. If used intermittently theymayhave a high sanitary value, and if made up partly of either animal or wood charcoal they remove more or less completely any offensive taste or odor which water may have. Security, however, requires doubtful water to be boiled.
In all cases arrangements should be made to protect the water from surface pollution, for convenient access for the men, and for watering horses.
(See the following books, treating on Military Hygiene in Camp and Garrison: Parker’s Practical Hygiene; Traité d’Hygiène Militaire, Morache; Manuel d’Hygiène militaire, Viry; Military Hygiene, Woodhull; the Soldier’s Pocket-book, Wolseley; etc., etc.)
1.Military Miningincludes all the operations necessary for placing charges of explosive underground and exploding them at the time desired, for the purpose of destroying the men, materials, or works in their vicinity, or for breaking up the surface of the ground either to advance or retard the operations of a siege.
The excavation for receiving thechargeis called thechamber. The approaches leading to the chamber when horizontal or somewhat inclined are calledgalleries, and when vertical are known asshafts. When very steep they are sometimes calledslopes. The charge, chamber, and approaches taken together constitute amine.
The pit formed by the explosion is called thecrater.
When the ground is homogeneous and its surface horizontal, the intersection of its surface by the crater is approximately a circle, the radius of which is called thecrater radius,AB,Pl. XI, Fig. 1.
The right line joining the centre of the charge with the nearest point of the surface toward which the explosion will take place, generally the surface of theground, is called theline of least resistance(written generally L. L. R.),C B,Pl. XI, Fig. 1.
A right line from the centre of the charge to the edge of the crater is called theradius of explosion,C D,Pl. XI, Fig. 1.
The distance from the centre of the charge at which an ordinary mining gallery will be broken in by the explosion is called theradius of rupture,C L,Pl. XI, Fig. 3. The radius of rupture varies in length with its inclination to the horizontal.
Craters whosediametersare once, twice, etc., their lines of least resistance are calledone-lined,two-lined, etc., craters.
Mines in which the L. L. R. is equal to thecrater radiusare calledcommon mines. (Their craters aretwo-lined.) Those in which the crater radius exceeds the L. L. R. are calledovercharged minesorglobes of compression; when it is less, they areundercharged mines; and when the charge is so small that no exterior crater is formed, they are known ascamouflets.
2.In the explosion of military mines on land it may safely be assumed that the circumstances of combustion of the charge when fired are such that the energy developed is directly proportional to the charge. A portion of this energy is generally lost by the escape of the compressed gases into the air, by the heat given up to the surrounding media, and by the transmission of earth-waves or shock; the remainder and greater part, however, is expended in rupturing the case containing the charge, compressing the soil in its immediate vicinity, separating that lifted up from that forming the sides of the crater, breaking up the portion thrown out into large or small fragments, projecting them to a greateror less distance, and disintegrating the soil around the crater to a distance which varies with the soil and with the quantity and character of the explosive used.
As the proportional part of the energy expended in each of the effects above named cannot be determined in any particular case, and as each case differs in some respect from every other, it is manifestly impossible to express in any mathematical formula a rule for determining the exact amount of explosive required for any particular mine.
From the results of long experience, however, engineers have concluded that computations sufficiently exact for practical purposes can be made upon the hypothesis thatfor common mines and those approximating closely to them in form, the volumes of the craters are directly proportional to the charges used.
3.In order to apply this rule in practice the volumes of craters formed by known charges must be measured; but since the soil in the immediate vicinity of the crater is more or less disintegrated, and the crater itself is partly filled up by the material which falls back into it, the outlines of the original crater cannot usually be recognized or its exact geometrical figure be determined. Besides, the craters formed under circumstances seemingly identical differ more or less among themselves.
For convenience in computation, however, several simple geometrical figures have been assumed as giving with sufficient accuracy the form of the crater of a common mine. SeePl. XI, Fig. 1. Among these Vauban assumed a cone,ACD, with its vertex at the centre of the charge; Valière a paraboloid of revolution,AHD, with its focus at the centre of the charge; Müller truncatedthis paraboloid by a horizontal plane through its focus; while Gumpertz and Lebrun adopted the form in common use at their time, and which has been generally accepted since, viz., a frustum of a cone,AEFD, the smaller base of which passes through the centre of the charge and has a radius,EC, equal to one-half the crater radius,AB(or one-half L. L. R.,CB).
The volumes of these figures are as follows:
The cone of Vauban (lately assumed also by Höfer) was abandoned as unsatisfactory, because it did not conform to the craters produced, and, as treated by Höfer, because the charges computed by its use were found to be too small (an error in the wrong direction). The paraboloid of Valière or Müller would seem to conform more nearly to the actual shape assumed by the crater; but it will be observed that the volume of the latter is sensibly the same as that of the truncated cone, and as the volume of earth thrown out is the quantity to be considered, the truncated cone will be assumed as the measure for it.
4.The principle that “the volumes of the craters are proportional to the charges used” is the general statement of theminer’s rule. AssumeCandC´to represent the charges of two mines whose volumes areVandV´, lines of least resistancelandl´, and crater radiirandr´. Assume also that the craters are frustums of cones, the radii of whose larger bases are twice those of the smaller. Then
or
Equation (1) is applicable tomines in which r does not differ materially from l or r´ from l´.
From an experimental mine giving a crater of this general type the relations betweenC,l, andrmay be determined, and assuming any two of the quantitiesC´,l´, andr´for a mine with a crater nearly similar in form, the other may be found from eq. (1).
Whenl = randl´ = r´, we have
and
Equation (2) is applicable to common mines, and shows thatin common mines the charge varies as the cube of the line of least resistance.
AssumingC´as the charge which will produce a crater with a volume of unity, equations (1) and (2) become, by omitting the primes fromlandr,
and
Equation (4) gives the rule for determining the charge for common mines whose L. L. R. is given, viz.:Multiply11/6, the cube of the line of least resistance in yards, by the quantity of explosive required to throw out one cubic yard.
The latter quantity is determined by experiment. A similar rule may be written out from eq. (3) for mines differing but little from common mines.
5.The quantity of gunpowder required to throw out a cubic yard of material has been calculated from a great number of mines fired in different kinds of soil. The following table gives the quantities required according to Lebrun and Macaulay, respectively the French and English authorities on the subject:8
6.Forcommon minesinordinary eartha convenient rule, very generally used, and which gives results nearly the same as those deduced from the table, is:
The charge of gunpowder in pounds is equal to one tenth the cube of the line ne of least resistance in feet, or