Underground Mining Operations in Warfare, WWII Tactical and Technical Trends, No. 29, July 15, 1943 (Lone Sentry)

Mining operations--not to be confused with the laying of ground mines--are a rather unusual but at times a vitally important phase of warfare, which may be called for when the "Fortress of Europe" is invaded. Its origin is ancient. In Roman days, if not earlier, mines were dug under city walls, and the props that held up the walls during the digging operations were then burned out, causing sections of the wall to collapse. In the First World War, mine warfare was carried on extensively in Flanders, culminating in actions at Messines and Wytschaete Ridges, where on 7 June 1917, the British troops, in preparation for their offensive of June 1917, blew out the large German position together with much of the crests of the ridges. On 13 March 1918, the greatest single blast in military history was effected by Austrian mining engineers against the Italian position on Mt. Pasubio, on the Adige about 40 miles north of Verona. It blew off the whole top of the mountain and turned it into something very like a volcano in full eruption.

The following pages have been selected from an article in the Pioneers' Quarterly (Vierteljahreshefte für Pioniere). Its author is reported to be a former engineer officer of the Austro-Hungarian Army and "one of the most experienced men in mine warfare." The article is dated May 1939.

a. The Surface Effects of a Mine

(1) General Considerations

Mine warfare is a part of tactics on the combat front; it differs from other tactical methods in the place of combat, underground, and therefore the method of conducting the combat is different. The proper weapon in mine combat is the mine, that is, the concentrated explosive charge completely enclosed in the earth.

The range of effect of this weapon is limited; 10 meters' range requires as much as 4,400 to 6,600 pounds of modern explosives, while a range of 20 meters requires as much as one and a half to two carloads.

The mine attack is for the purpose of destroying both personnel and materiel of the enemy by its effect at the surface. The operations that follow the blast are not our concern. For the mining engineer officer, the decisive element is the mine crater itself.

(2) Craters

(a) Craters in Earth

By the effect of a single explosive charge sunk in the earth, the mass of earth lying above it is thrown out (see Fig. 1). In figure 1, M--M 1 is the surface of the earth; B and B 1, the edge of the crater; B--D--B 1, the crater initially blasted; and B--J--B 1 the crater actually resulting. The crater radius is B--A or A--B 1. K and K 1 are the crater crown, A--J the depth, and A--O the depth of the charge to the center of the charge (O), which is the shortest line of resistance. The dislodged earth-core can only be a cone, and in its place there remains in the earth a crater of equivalent size. This cone of earth is hurled vertically by the explosive charge and breaks up in the air; then almost all of it falls back into the crater. For an excellent illustration of a typical blast, see figure 2. The crater is refilled in large part to approximately two thirds of its depth, while the remainder of the erupted earth drops within a short radius on the edges of the crater and forms the crater crown. A small portion of the earth in the air, the "crater cone," is more widely scattered, and is called the "crater spread."

[Fig. 1: Underground Mining Operations in Warfare]
Fig. 1

The magnitude of the crater effect can quite generally, as a rule of thumb, be determined by the following method:

The radius of the presumed circular crater cavity is normally equal to the depth at which the charge was placed. Whenever, therefore, the charge lies at a depth of 33 feet,* then the crater diameter is also 33 feet and the diameter of the crater cavity 65 feet. (This would be the effect of a charge of about 4,400 to 6,600 pounds of demolition explosive.) The ultimate crater depth is, as mentioned, one-third of this magnitude; with a crater radius of 33 feet, therefore, a crater depth of 9 to 10 feet measured from the surface of the earth. The height of the crater crown is fixed at about one-third of the crater depth; in our example, accordingly, 3 to 4 feet.

Figure 2 illustrates the beehive shape of the "crater cone" or earth hurled up by the blast of a standard mine containing 771 pounds of HE in alluvial gravel. At the top of the cone, corresponding to the cubical shape of the charge, extend the 4 "peaks." The cones of overcharged mines open at the top in a form of a bouquet, while weakly charged mines produce cones ranging in appearance from a cake down to a simple oval skullcap. In this way, from the shape of the "crater cone" alone, conclusions can be drawn as to the strength of the charge, the type of mine, and even the ground conditions. The crater cone of dispersion, that is, the height to which the earth is propelled, is usually twice the depth of charge. With a charge depth of 33 feet, therefore, the crater cone would rise to 66 feet.

[Fig. 2: Underground Mining Operations in Warfare]
Fig. 2

The crater scatter usually reaches the same dimensions as the crater cone. The limits of the crater scatter are difficult to determine conclusively. A lethal effect outside the area stated, however, is not to be assumed in any case. Occasional accidents due to stones, etc., cannot be given any consideration as risks in war. Precaution should be practiced however; in peacetime training maintain a cleared zone of 1,000 feet on all sides.

The crater, plus the scatter, represents the actual zone of destruction on the earth's surface; in our example, therefore, with 66 feet of scatter plus 66 feet of crater plus 66 feet of scatter, we have a total of 198 feet. This--and here is the point to emphasize--is the absolute limit of the external effect. Within such a zone living men as well as the material will be destroyed or buried. Outside these limits the mine has almost no real effect.

Naturally, the attacker will apply himself to the accomplishment of this final result of his exertions and combat by making the external destruction as comprehensive as possible. To a certain degree, this can be achieved by heavier charging of the mine--overcharging. However, overcharging involves a serious disadvantage--an enormous increase in consumption of explosive. Today this has even greater weight, since mine galleries, because of the effect of artillery, must lie at least 39 feet and if possible even deeper, below the earth's surface. The size of the charge, however, increases as the cube of the crater radius. If a crater 49 feet in radius with a charge depth of 49 feet requires about 14,887 pounds of ammunition, a crater twice the size, with a radius of 98 feet and the same depth of charge, requires 2³ x 14,887, or 119,016 pounds of demolition explosive; and one three times the size, with a radius of 144 feet and the same charge depth of 49 feet, requires 3³ x 14,877, or 401,679 pounds. Craters with diameters larger than 3 times the depth of charge cannot be blasted.

With the increase in the crater radius of such overcharged mines, the scatter also increases sharply--by the third power, with, however, an increase in the volume of erupted matter by only the second power; accordingly, such a mine also operates like an ordinary land mine, (Note: The land-mine effect is produced by the increased scatter, as the erupted material is blown far away instead of falling back in the vicinity of the crater with burying effect.)

(b) The Mines in the Wytschaete Bend

The following data relating to mine craters was taken from the work by Major Kranz entitled "Mine Combat and Military Geology in the Wytschaete Bend" (Minierkampf und Kriegsgeologie im Wytschaetebogen) appearing in No. 3 (1935) of The Pioneer Quarterly. At Wytschaete and Messines Ridges on 7 June 1917, the British set off 19 mines in the watery clay of the Flanders flat-lands.

Some of the largest craters, with a charge of approximately 35 tons of ammonal, which is 1.05 times as powerful as TNT, at a charge depth of 97.8 feet had the following dimensions:

Diameter 265 ft

Width of crater crown 60 ft

Height of crater crown 17 ft

Depth of crater 51 ft

The largest single charge used by the British in the Wytschaete Bend amounted to 95,573 pounds of ammonal, which with a charge depth of 125 feet produced a crater of 165 feet in diameter and 17 feet in depth.

If we average the 19 mines used on 7 June 1917 in the Wytschaete Bend, all of them gigantic mines with a total outlay of 913,315 pounds of demolition explosives, we obtain:

Crater diameter         182 ft

Width of crater, crown         62.5 ft

Depth of crater         26 ft

Let us assume that each mine is placed in the most unfavorable position for the defender, i.e., perpendicularly Deiow the combat position.** We then see that the position under attack is disturbed by one mine for a width running across the entire crater and the two outside crater crowns, that is 182 + (2 x 62.5), or 307 feet, and in the depth of the position by the half crater + one crater crown, that is 91 + 62.5, or 153.5 feet.

This is the absolute total effect of one such mine on the earth's surface.

In all, the 19 British mines blew up a length of 2,000 yards in the 10.6 miles of the German front line attacked, or about one-tenth of it.

In mountain rock, the mine effect is fundamentally the same as in soil. The charges, corresponding to the greater resistance of rock, must be made larger. The form of the surface effect is strongly influenced by the conformation of the terrain; this must, of course, be given due consideration in the plan of attack and in placing the mine. Here too, in fact, we also see quite regular craters, like those on Mt. Cimone and the Col di Lana where the flat and almost uniform conformation of the surface of impact permitted such a result.

On the other hand, however, we note mines with quite peculiar external effects, sometimes intended, sometimes unintended. Such, for example, was the case of Mt. Pasubio, where by the blasting of two lateral craters, the rock mass supporting the enemy emplacement was brought to collapse (see Figs. 3 & 3a)--Both sketches are schematic only and not to scale. Figure 3 is the plan for the final blast on 18 March 1918, and 3a, the approximate position of the Italian and Austrian mine galleries. It would appear that the Austrian galleries were driven below those of the Italians.

[Fig. 3: Underground Mining Operations in Warfare]
Fig. 3

b. The Subterranean Effect of the Mine

(1) General

The effect of the explosive with which the mine is charged, on its explosion is an impact generated in a fraction of a second. This impact operates with equal force in all directions, therefore in a spherical form. This is the start of the effect of every mine, quite independent of how this effect is later transmitted.

The impact is propagated in the earth, so long as it has sufficient force to overcome the quite considerable resistance of the soil and rock. It is finally dissipated if the mine lies deep enough in the earth, or reaches a point somewhere at which the resistance is weaker and gives way completely. The impact then behaves as a thrust and hurls the portion of the earth which still offers resistance into the air; the mine comes into the open and produces the crater.

[Fig. 4: Underground Mining Operations in Warfare]
Fig. 4

(2) The Camouflet, or Completely Subterranean Mine

In the first case of the dissipation of the wave of concussion, there can be only a subterranean effect, and the mine therefore acts only underground; it is then called a "camouflet" (figs. 4 & 5), a crushing or damped mine. It is easy to see that the camouflet can utilize in subterranean effect the force it economizes in comparison with the crater mine.

[Fig. 5: Underground Mining Operations in Warfare]
Fig. 5

A distinction is therefore made between the crater mine with both surface (external) and underground effect, and the camouflet with a somewhat greater destructive effect, but entirely underground.

The officer in charge should recognize that the crater mines primarily of interest to him have not only a surface effect due to excavation of crater, lateral burying effect, and scatter, but have their subterranean effect as well against one's own dugouts, shelters, etc., below the earth's surface. This underground effect reaches approximately the same magnitude as the surface effect, but in a spherical form in all directions around the mine.

One more point should also be mentioned here: that the camouflet is of primary interest to the miner for his own combat. This form of mine is his weapon, in fact his weapon exclusively. The crater mine is only the final objective of his work. Until he reaches this objective, in the course of mine combat he will have to apply many camouflets, for it is with them that miners fight in subterranean combat, defenders work to ward off the subterranean enemy, and the attacker strives to cut his way through the subterranean defense installations. To make use of the crater mine before reaching the final objective is always an error on the part of the defender, and is an error in most cases on the part of the attacker, if either does not by so doing promote some other major purpose.

(3) The Gas Effect of the Mine

We know that the explosive effect occurs as the result of the transformation of the explosive into a tremendous volume of gas under intense pressure and at a high temperature, with the volume and quantity of gas persisting for some time after the blasting. These effects then are dissipated in the vicinity of the mine with cooling of the gases and loss of pressure.

These gases, or more properly, this gas composite, are a compound of various gases and vapors, of which carbon monoxide only, because of its dangerous properties and the quantity that is produced in blasting, is of interest to our discussion. Carbon monoxide is colorless and extremely poisonous. There is no warning of it. Inhaled in even slight quantities, it has a fatal effect. Mixed with atmospheric air, it burns, and with a certain ratio of mixture it becomes highly explosive. The gas masks used in the last war provided no protection whatever against it, and only the inhalator equipment generating breathable air itself could give protection against the poisonous effect.

This gas production, a secondary result of the mine, can often become the major consequence. It is equally dangerous for friend and foe. Frequently, along with the poisonous effect, the entire volume of gas will ignite, produce explosions in various places, and, by setting fire to structural material or stores, cause stubborn fires in the emplacements. Some examples from the history of war will explain and illustrate the point; while from earlier wars many examples are on record of serious catastrophes due to the gas effects of mines, we shall confine ourselves to those from the last war. In the Italian mine blasting on the Castelletto, the blast gases made the mine galleries, which had to be designed to serve tactical purposes as well, unusable for 2 days after the shot. The attack-column, dashing forward from the gallery immediately after the blast, was overcome immediately by the gas and suffered extremely heavy losses in gassed and dead. We read in the descriptions of the mines in the Wytschaete Bend on 7 June 1917 of the blazing sea of blue flames in the bottom of the gigantic craters. On the Lagazuoi in the Dolomites in 1917, a persistent fire was reported in the craters produced by the Austro-Hungarian blasting of 22 May which made any approach to the crater impossible because of the heat it generated. Finally, on Mt. Pasubio, as a result of the peculiarity of the mountain structure, the gas effect played a part in each of the 11 blastings done in the course of the mine combat and led to serious losses among the Austro-Hungarian troops. Thus, on 2 October 1917, when Austro-Hungarian miner and assault patrols hurried into the quite open and absolutely undamaged galleries following the Italian blasting, they suddenly dropped as if struck by lightning. In the final Austro-Hungarian blast on 13 March 1918, absolutely the greatest blasting of military history, the entire mass of Mt. Pasubio was enveloped in flames, and jets shot out from the Italian gallery exits for a distance of 100 feet during a period of hours.

This phenomenon in mine combat, which results in far greater casualties than the purely mechanical effect of the mine, should be given much more attention than was given it in the war of 1914-1918.

c. The Mine in Combat against Modern Fixed Fortifications

For obvious reasons, within the scope of this article we shall attempt to speak only quite generally on the topic of mine combat against fixed fortifications. Here the important point is the absolutely static position of one party, the defender. From this fact arises all the peculiarities of the situation from the operational, tactical, and also the mining viewpoints. The battle for fixed fortifications must be fought out on the spot. While in field warfare a local withdrawal from the vicinity of a known mine can usually be made without great tactical loss, such a retreat often can not be made from a fortified position without endangering the whole front. The possibility of underground combat against such fortifications must be regarded as ever present.

Because the forward area of permanent fortifications is prepared and completely dominated by the defender, greater underground distances will also have to be overcome at the start of the attacker's subterranean activity. In attack on permanent fortifications the opportunity for a short mine combat with a surprise effect on the enemy will scarcely ever arise. A second determining factor in the situation stems from the consideration that the attacker will always meet an enemy prepared for underground warfare. The attacking miner is faced with a difficult battle with an enemy who has reconnoitered the details of a possible mine attack in advance, on the basis of his defensive system built up in time of peace. He now lies in wait like a spider in this thoroughly planned system and can operate effectively against the attacker everywhere and almost without danger to himself. The attacker will have to consider giving the underground attack a more prompt and systematic development by increased provision of personnel and equipment. For this reason numerous organizations capable of conducting such work will have to be in readiness, and in addition, units trained in mine combat and organized solely for this purpose, as well as columns and stores of machines, tools, and material.

From the standpoint of mine tactics, the attacker has the advantage that he is subject to only the one limitation--that in any case, the attack objective must be reached. The final objective of the underground attack against fixed fortifications is never, or only rarely, the mine effect on the earth's surface, but rather the fortified installations of the enemy, positions that cannot be reached by artillery fire, such as the substructures of gun and machine-gun turrets. The matter is therefore one of purely demolition mines, quite similar in placement to the crater mine, with their depth depending upon the effect to be obtained against those targets.

d. Underground Combat

(1) General

Without a knowledge of its tactical method of employment, it is impossible to understand the use of any weapon. The following sections will outline, principles which every commander should know on the subject of underground combat. These suggestions are not intended to be a complete guide to independent leadership of underground warfare, but rather an explanation of methods which should be generally understood by members of the land forces.

(2) Reconnaissance

The greatest attention must be paid to reconnaissance. As has been apparent from the history of warfare, especially from the accounts of the last war, no complete surprise of the enemy has been achieved in any mine operation. On the other hand, rumors and warnings at the front often led to the starting of countermine operations against a suspected subterranean attack in places where the enemy had, in fact, not the least intention of mining, and often where circumstances excluded any real mine danger.

But the object of reconnaissance is not merely to recognize enemy subterranean activities; it is to effect this speedily enough to gain time and take countermeasures. For evaluating the results of reconnaissance, fundamental mine training experience is indispensable. Hasty or incorrect conclusions have unfailingly led to underground combat, whether desired or not, for it must be assumed that all mining operations will come to the knowledge of the enemy and force him, in turn, to take his own countermeasures. The miner has no means of reconnoitering underground with any assurance of success other than by digging tunnels and shafts. The enemy becomes aware only of this excavation; its purpose remains unknown. In order to protect himself he must then do the same, and by reason of the short distance that separates the two forces, this operation necessarily leads to combat, and to combat which can end only by the evacuation of the underground region by one side or the other. Such was the case in all mine battles of World War I, in the Wytschaete Bend as well as on the Dolzok in Bessarabia, on Mt. Sief as well as on the Lagazuoi in the Dolomites.

(a) Reports

The treatment given to intelligence reports, especially those based On statements of prisoners, is the same as that given to all other reports in time of war. Only mining experts should be brought in for the examination and questioning of prisoners on the subject of mine operations. Otherwise, because the subject is equally foreign both to the prisoners and the ordinary examiner, the most unbelievable kind of reports will appear. Moreover, even reliable reports must be accepted with reservation. In the late autumn of 1917, for example, the report came to Mt. Pasubio from foreign sources, that in northern Italy a few special detachments of professional miners, and tunnel and quarry workers, were being formed and sent into the Pasubio region. While the statement was entirely correct, these detachments were, in fact, assembled for extensive highway construction with curved tunnels and galleries on the Pasubio massif, and had nothing to do with mine warfare.

(b) Observation

Observation can yield data which, when assembled, give a basis for estimating any underground activity of the enemy. Many conclusions can be drawn from the nature of the earth spoil. Here, geological observations are of special value. With continuity in observation which may disclose the scope of enemy work and its position in depth, miners need not without urgent reason be withdrawn from work that has been started, and thoroughly trained units need never be left behind underground should a sudden evacuation of the works become necessary.

Snowfall facilitates the recognition of large quantities of excavated material. Aerial reconnaissance should be carried out for the study of enemy diggings, as well as to locate the entrances to his mines, always carefully concealed from ground observation. In spite of the inadequacy of the reports, air reconnaissance in mine attack against permanent fortifications and mine systems prepared as a part of the fortifications is the only means of getting information in the first phases of combat. Clear and positive results, however, can consistently be expected only through subterranean reconnaissance.

i. General

Reconnaissance underground is done by ear. To completely reconnoiter the combat terrain, every means should be used to extend the sense of hearing in both vertical and horizontal directions. In the horizontal direction galleries are employed, and in the vertical direction, shafts. Listening apparatus must be installed to give the ear increased range, and arrangements made for organizing and coordinating the listening service.

ii. Listening Service

The listening service is furnished by individual listening posts in the galleries, and the men who man them must be thoroughly trained in sound detection. The work of the sound-detection miner is difficult. To lie for hours in a dark, wet hole underground, with your ear pressed to the ground, in constant uncertainty about your own fate, your head crammed full of imagined suspicious whispers and--what is of great importance--without the possibility of any comparison with the results at other listening posts--all this imposes severe demands on the listener.

The mine listener should be at home in any terrain, in any type of earth. He must know how the different types of soil transmit sound and how far they propagate them, and in order to understand all that can happen in mine warfare and so connect certain noises with particular phases of underground activities, he must be a military miner himself. The trainee miner well knows how to distinguish sounds of engines, and whether a two-hammer or single-hammer unit is working. He knows the number of points where work is going on, and the number of drills (which, incidentally, are recognized as a sharper tap and never as a dull thud in rock). He must know whether the enemy is working in a gallery, in a mine chamber, or in a trench. Many times he can determine from the sound itself that most important moment in mine combat, namely, when the enemy is about to blast. In the mine combat on the Colbricon, a porphyry horn just beside the Rolle Pass (see fig. 6), the entire endangered region was evacuated, on the basis of what had been heard, 2 hours before the Italian blast. The regrouping for the occupation of the crater was then organized--in this case, of course, only a reoccupation of the expected debris-zone. All this was done without difficulty and not a man of the garrison was lost; the position was immediately reoccupied and a few minutes after the blasting it was as ready for combat as it had been before.

iii. Sound-Detection Pauses

For the carrying out of the sound-detection service, sound-detection pauses in the entire listening area must be ordered by the commander. In these pauses every noise and all speech in the emplacement are to be discontinued, even on the surface. Such pauses are to be made at irregular time intervals according to the directions of the mine officer. What mistakes can occur is well illustrated in the following instance: On 24 January 1917 under Mt. Pasubio, clear voices and the sound of rolling equipment could be heard in the midst of the Austrian gallery. According to the sounds, the enemy seemed to be already under the Austrian position. A committee met, listened and came to the same conclusion; then, a short time later, the voices were recognized as Tyrolean. In one of our own dugouts they had been paying no attention to the sound-detection pauses.

[Fig. 6: Underground Mining Operations in Warfare]
Fig. 6

The sound-detection service has been given greater space here intentionally, for it is of absolutely vital importance in mine combats. Everything depends on its reliable operation.

(3) The Underground Advance (Extension of Mine Construction)

(a) General

The distinction between offense and defense underground is difficult to maintain. The objective of the miner under all circumstances must be that of attacking the enemy's combat emplacements without involving his own. This is his duty, assigned exclusively to him; and his comrades in the surface fortifications must be able to rely on him. Therefore, the immediate mission of the subterranean defenders, whenever they learn of the intention and direction of the attacker, is to counterattack as far to the front as possible.

(b) Galleries and Shafts

The underground advance proceeds by way of galleries and shafts. Just as the troop-columns, whenever possible, utilize good, straight roads with shelters, supply, and other facilities, the same is true in the underground advance. The advance must be started with large galleries, for these passages must provide a clear roadway for the miners, with their loads of tools, respirator apparatus, and other material. The galleries must allow space for assembly areas and room for the storage of tools and tamping, blasting, and detonating materiel; for such transport arrangements as pushcart tracks and cable transport; for ventilation equipment with pipes a foot in diameter and drainage conduits, and often, also, for high and low tension cables, which must be kept at a distance from each other (fig. 7). Above on the right are the 12-inch ventilation tubes; on the side wall beneath are the low tension conduits for the sound-detection apparatus, as well as for the alarm and gas-alarm system. On the left is the practically noiseless suspension cableway, and at the extreme left, the high tension cable for the gallery lighting plant.

[Fig. 7: Underground Mining Operations in Warfare]
Fig. 7

After work has begun, any enlargement of the passageways can be done only in galleries cut in solid rock. (Note: This is due to the difficulty of side-bracing in earth.) Because of the effect of artillery fire, all structures must be built at least 60 feet underground, and any subsequent enlargement can be carried out only under great difficulty and with temporary loss of utility. To start with a cross section of small diameter, because of haste and urgency, has been shown in almost every case to be a mistake. As the galleries become longer, branch passages become necessary, imposing greater demands on transportation, traffic, and the bringing in of equipment.

For the beginning of the mine construction, beyond contact with the underground enemy, a gallery profile 4.5 feet high and 3.9 feet wide in the upper third, or 3.9 feet in diameter, will be the minimum dimension.**** With further training and practice, under certain circumstances smaller dimensions can later be applied, with a smaller amount of labor and cubic volume of material to transport.

At this point another war experience should be mentioned. This is the requirement of complete separation of mine construction from other tactical installations; otherwise the miner is seriously impaired in the performance of his duty of protecting the troops against the effects of underground events. Moreover, the maintenance of the secrecy of underground work is also made difficult. For example, in addition to the information from prisoners and deserters on this subject, we read in the reports from the Bessarabian front how, before each listening pause, a few mortar bombs were fired against the suspected enemy gallery entrances, whereupon in our galleries there could immediately be heard the sound of the running feet of the enemy garrison in their own mine galleries, and from this valuable inferences as to distances, etc., could be drawn. In close relationship to the requirement of secrecy, is that even more urgent need of exclusive subordination of mine work and miners to leaders of their own arms of the service, or under the higher HQ command, in order to be independent of the junior front-line commanders. Miners then will not be constantly used for other work which may seem more desirable to the local garrison. Otherwise, when the enemy has done his blasting, we will wonder why no precautions, or too few, had been taken on our own side. For experienced miners, historical military examples need not be quoted; they are not hard to find.

(d) Time Estimates

The efficiency of the miners' effort depends on a great many circumstances, but for the most part on the degree of their training. Within broad limits, the following time allowances may apply.

i. In Earth (with a high degree of training and normal conditions, such as good lighting and ventilation, previously prepared shoring material, etc.):

Shafts (per linear meter) . . . . . . . . 5 hours min., 9 1/2 hours max.

Galleries (per linear meter) . . . . . . . 4 hours min., 9 hours max.

In loam and clayey soil, a minimum of 1 hour and a maximum of 2 hours per linear meter, according to the length of the gallery, were required for hand removal at a distance from the enemy. In proximity to the enemy the rate dropped to 1.50 meters per day.

ii. In Rock. The achievements reported in the last war are absolutely undependable. They suggest, for a passage cross-section of 32 to 40 inches, an advance of 30 to 32 inches per hour with machinery, and 8 to 12 inches by hand. According to experience, however, the figures of 12 inches by hand and about 40 inches with the mechanical drill were the approximate daily, not hourly, work-accomplishment with our untrained soldiers. On Mt. Pasubio the Italians calculated, for their certainly well-trained stone workers, 80 inches of gallery advance per day.

e. Summary

(1) The weapon of mine combat, the mine itself, is almost absolutely certain of its objective in view of the small sphere of effect and the all-around uniform effect in every direction. The size of the mine is to be determined on the basis of its purpose, and can therefore always be accurately adapted to the nature and resistance of the objective. With the possibility of an unlimited increase in charges, the effect can also be practically unlimited in its concentration at one point. As regards casualties, the blasting effect can also be increased at will be means of the gas effect.

(2) The great moral effect of mine combat, from the beginning of suspicion that it is underway up to the detonation of the mine itself, has been repeatedly shown by military history. It is extremely difficult to counteract. Because subterranean attack can be made almost anywhere, the threat of its use is liable to be widely felt.

(3) The underground conduct of battle, can be opposed only underground. It must be reconnoitered underground, with a very great outlay in time, work, and material. Combatting it on and above the surface is possible only to a limited extent, and under no circumstances with lasting success.

(4) Underground resistance to mine attack by means of mine defense, corresponding to the information disclosed by thorough reconnaissance, always can be a laborious process, involves many times the quantity of supplies and personnel as required by the attacker. In most cases only the installation of a complete and organized underground defense system will have any prospect of success.

(5) Because the site of combat is in the earth, and because of the extensive and difficult work required, the underground mode of battle is a very slow one and requires a great outlay of special troops and equipment. Its employment is therefore justified only against the most profitable objectives.

(6) The site of combat underground, where only one human sense, hearing, is capable of giving warning, stamps the underground mode of combat with the mark of something unknown, something uncertain, which often forces both sides to take up underground combat, unwillingly, and thereby to lose the advantage that rests with aggressive mining operations. This uncertainty also makes it difficult to evaluate the plan and the intention of the enemy, the phases of the battle, and the prospects of success.

(7) The abandonment of the combat area, which is one way of meeting a threatened mining attack, implies a locally limited failure in the campaign. However, it is an absolute defeat in the combat for permanent fortifications, confined to a limited locality, with their system of mutually supporting defenses. For this reason permanent fortifications have always been a proper field for mine combat.

(8) Uncertainty always makes mine combat an expensive, tedious method of battle, seeming to the non-expert more of a hidden game of chance than an open combat. It can be met only by a firm will based on one's own knowledge of mine operations.

(9) Lack of technical knowledge is apt to arouse the belief that luck alone is the controlling factor in mine combat. Luck certainly belongs there, but no more than in any other form of combat.

* All data are translations of metric terms except as stated otherwise.

** In practice, however, this is not frequent for the following reasons:
1. The attacker, in using the mine, will try to demolish the obstacle placed in front of the position.
2. The long work directly below the feet of the enemy is in no sense a comfortable matter. The placing of the mine itself (construction of the mine chamber, charging, attaching fuse connections, and tamping with truckloads of sand bags, concrete and steel, or wooden beams) takes a week or even longer. For this reason one is satisfied in most cases to have the blasting effect merely reach the enemy position.

***The author has had no experience whatever with the new geophysical soil investigations and their applicability in the field of mine warfare.

****Note: This is a literal translation of the German. The types of cross section implied in the statement are not clear, and no illustrations are given in the original.