Change from Battle Lines to Trenches of a Position.During a battle, as we understand it in open warfare, as soon as the fighting lines are halted for any reason, every man immediately begins to dig in for shelter against the enemy’s fire. If the halting of these fighting lines is more or less permanent these “skirmish holes” are connected, and we have thebeginning of a rude trench. We must remember that in a battle troops are disposed in depth in a series of lines. All these lines dig for protection in a similar manner, giving the beginning of several lines of trenches. If the troops remain for any time in this position, it is necessary to have routes from the rear to the front to carry up ammunition and supplies to the different lines. These communication routes are also dug in, and we have the beginning of communicating trenches. Soon the men will begin to seek better protection against rain, cold, and overhead fire, and build themselves some kind of shelters. In a similar manner command posts and supply depots are established.
In time there is a complete skeleton of a series of lines of trenches outlining a position. If the mission of the troops is to remain and hold the ground, the necessary plan of organization for the final position will have to be based upon this skeleton. The purpose of this new organization, as we have noted, is to establish the position so that the ground can be held by fewer troops.
Active and Passive Elements of a Position, Especially Support Points.The first fire trench of a position is continuous, but it is not good practice to man the whole of this line,because this would take too many men and defeat the purpose of the fortifications. Secondly, a better defense can be established by garrisoning a series of strong points, or salients, from which can be obtained flanking fire. In the first line these are called support points. The trenches connecting these support points are retained as such, but are not usually manned. This curtain trench, so to speak, is retained for communicating purposes, and to deceive the enemy as to the real points of defense. A few watchers are left in it.
The first line, then, is a series of support points, well defended by men and special weapons, and at such distances apart as to support each other.
Division of Position.The garrison of such a support point in the first line is a company, and the captain is responsible for the holding of this ground. (The platoon, we must remember, is a tactical unit.) In dividing the first line into these active elements the size of each support point depends upon the importance of the ground or of the tactical situation.
Similar natural strong points are also located in the second line. They will be fewer and farther apart in this line than in the first line, which is exposed to hostile attacks. These points in the second line are connected with the support points and together the group is called a center of resistance. The command of such a center of resistance, including one or two support points in the front line, falls to a battalion commander with his unit. For example, the area of a center of resistance under the command of a Bn. C. O. will include, say, two support points in the first line with a company in each, and the strong point in the second line with two companies.
In the third line, also, natural strong points are located and organized for defense. The command of this strong point, including, let us say, two centers of resistance, falls to a colonel with his regiment. Such an area is called a sector, or a sub-sector. If it is a sub-sector two such constitute a sector in command of a brigadier-general.
Different Lines of a Sector.We have now arrived automatically at the fact that each sector is composed of a series of lines in depth, each defended in strong points.
The first line is termed the line of resistance, as the first defense is made against the enemy’s attacks in the support points of this line.
The second, or main line of resistance, is called the support line. In the strong points of the centers of resistance are the reserves and the headquarters of the battalion commanders.
The third line is called the covering line of the artillery, because it defends the batteries distributed behind it. It also contains the reserve troops of the sector, a battalion usually holding each strong point. Here are established the headquarters of the colonel and the different central depots of the sector.
The above three lines constitute one position. There may be several positions in depth at distances of three miles or more apart. Usually there are two positions and sometimes three. It is said that the Germans have as many as six positions in depth in places. The first position only, of course, is permanently occupied.
Advantages of the Continuous Trench.The continuous or curtain trench between support points must not be eliminated for several reasons. The trench will deceive the enemy as to the location of the elements of support points. If this trench were absent the enemy could easily locate these, and subject them to concentrated artillery fire. The position cannot be hidden from airplane observation but the essential elements, such as emplacements, dugouts, etc., must be concealed.
Traces of Trenches Used to obtain Flanking Fire Types of Communicating Trenches.
The curtain trench serves for communicating purposes for lateral movements of troops and for liaison between neighboring units.
The absence of the curtain trench would leave breaches in the line where in a general attack units could concentrate and break through. In such a general attack the curtain trench is occupied and defended by the reserves. Barbed wire, of course, protects the entire front.
These trenches also serve, if necessary, as cover for reserves acting as reinforcements to the adjacent support points, as there is only sufficient shelter in a support point for its own permanent garrison.
Lastly they may serve as trenches of departure in the offensive.
Importance of Flanking Fire.It is possible to have the support points at intervals because flanking fire from these will command all ground in front. The importance of flanking fire cannot be overestimated. Everything must be done to obtain it.
Type of a Good Entanglement in front of a Firing Line Without Salients To Obtain Flanking Fire
Sometimes it is impossible to obtain flanking fire because of lack of salients. If this is true the trace of the first line trench must be rectified to give flanking fire along the line as per diagram.
When neither of these two methods is possible small combat posts with machine guns are located in advance of the line to obtain flanking fire.
The machine gun is the best weapon for flanking fire. Several emplacements are constructed for each machine gun, but during the bombardment it is kept under cover in a dugout. When the attack develops the machine gun is quickly set up in the proper emplacement. If kept in a permanent emplacement the enemy will soon locate it and put it out of business by artillery fire.
If no emplacements are possible or if they are destroyed machine guns are operated on open ground or in shell holes.
Field of Fire.With proper flanking fire a line can be defended with a shorter field of fire than otherwise. A hundred yards of field of fire is sufficient with good flanking fire and accessory defenses, such as barbed wire, etc.
DIVISION OF POSITION INTO COMPARTMENTS FOR INTERIOR DEFENSE
Location of Trenches.Lines of trenches which are the result of a battle are not always located in the most logical positions. They are the results of the exigencies of the battle. However, it is well to know the best locations for the trenches of a position under different conditions in order to place them there when possible.
In flat country, of course, it makes no difference where the trenches are located. On the profile of a hill, however, the question is where to locate the first and where to locate the second line. Let us consider Figure 15. Point A is out of the question as you have no view of the enemy. At B you can observe the enemy’s line and he can observe yours. However, the enemy can shell you at this point and observe the results. At C the same conditions obtain as at B, except there is a dead angle directly in front. At D you cannot observe the enemy nor can the enemy observe your line. From these considerations we see that the proper location for the first line will be at B as you must be able to observe the enemy and all the ground in front. Your second line should be located at D where the enemy cannot observe and bombard your position. At D the line can be made as elaborate as you have time, men, and material, because you are more or less unmolested by the enemy’s fire and observation.
The reverse slope is of the very greatestimportance in organizing a position. Movements of troops and supplies can be easily accomplished here under cover. Deep dugouts can be constructed with the least work. But the greatest advantage lies during the bombardment. The enemy is not able to observe the accuracy of his fire on the reverse slope so that the elements in this line are left more or less intact. For this reason the line on the reverse slope becomes the most important line of resistance against the enemy’s attacks. The Germans habitually organize their reverse slopes very strongly.
Division of the Position into Defensive Compartments.We have already spoken of the sector in depth by successive lines. In the same way it is necessary to organize the positions for lateral defense. A support point may be captured by the enemy and from this ground he can launch a flanking attack on the adjacent part of the position. It is necessary that there should be an established defense against such an attack, and for this purpose each sector is divided into compartments, so to speak, with all-around defense.
Boyaux or communicating trenches on the flanks of these compartments are organized as firing lines with barbed wire belts running parallel and with machine guns disposed forflanking fire. We have then each sector cut up into compartments capable of independent resistance in all directions, if the surrounding compartments are captured by the enemy. Such a compartment also has the advantage of serving as a base for a counterattack against an adjoining one that has fallen into the hands of the enemy.
In a sector the responsibility of such lateral defenses falls especially upon the colonel.
Concealment.All of the essential elements of a position, emplacements, dugouts, etc., are more or less without value if they can be seen by the enemy and subjected to heavy artillery fire. Everything that is possible must be constructed without the observation of the enemy.
It is important to hide your works by making them fit in with the color scheme and shape of the surrounding ground. False or dummy trenches, emplacements, shelters, etc., are constructed to cause the enemy to waste his ammunition. The art of camouflage is also extensively employed for this purpose against both ground and aërial observation.
Plan of Organization.We have seen thatthe first outline of the trenches left as a consequence of the battle must be modified in detail to obtain better protection and organization. The complete plan of reorganization is laid down by the commander of the sector and is called the Plan of Organization.
This plan is drawn up as soon as the position has a permanent garrison. The Plan of Organization must be faithfully followed by all the successive garrisons of the sector. After its adoption, even the commander of the sector himself cannot modify the plan without the consent of the general in charge.
The real value of the position depends upon the amount of continuous work that has been done in carrying out the original plan.
Outline of the First Line.As was seen before, the original trace of the first line was established as a consequence of the needs of the battle. In the organization plan, it is necessary to introduce several modifications in this trace. The commander responsible for this change should place himself in the situation of the enemy and consider an attack upon his own lines. From this consideration he will introduce such modifications as will make this task as difficult as possible.
The responsibility of making this modification in the trace of the first line does notdevolve upon the captain in the first line. As a rule if it were left to him few changes would be made because of lack of initiative on his part, or because of fear that if the line were captured he would be blamed for having changed it. This task falls upon the battalion commander who is responsible for the center of resistance, with the consent of the sector commander. The reason for this is that the sector commander is the only one of these officers who knows the subsequent use of this particular sector, whether for defensive or offensive purposes. If for defensive purposes the line may be carried as close to the enemy’s line as possible. If the sector is being organized for an offensive there must be enough distance between to keep his own line out of the zone of artillery dispersion when the target is the enemy’s line.
Cover Trench.In general all fire trenches have a second trench behind, called the doubling or cover trench. The use of the cover trench is not primarily for defensive purposes. It has special uses.
The majority of the troops in the first line are kept in the cover trench in shelters located there. The first line is habitually manned by only a sufficient number of men to assure observation and security. The rest of the garrison remains in the shelters of the cover trench to get as much rest as possible. It is very important that comfortable shelters be located in the doubling trench. If troops are exposed to the elements and bombardment their value decreases very rapidly. If the shelling becomes too severe the men in the first line retire to the shelters of the cover trench until the attack develops.
Another use of the cover trench in the defensive is to keep here a necessary number of troops for reinforcing the first line when necessary and for counterattack against the same if it is taken. This latter use establishes the distance between the two lines, which is from thirty to forty yards, so that hand grenades can be thrown from the cover trench into the first line.
Behind each support point there is usually a lateral communicating ditch called the circulating ditch which should not be confused with the cover trench.
Advance Posts.In front of the firing line certain advance posts are established. There are three kinds of these: listening, observation, and combat posts.
Thelistening postis not under the control of the commander of the support point but is in the service of the Intelligence Officer.It is furnished with a microphone for the purpose of picking up enemy’s telephone messages in the hostile line.
Theobservation postbelongs to the sector and is used for purposes of observation and security.
OBSERVATION POST
Thecombat postis established to obtain flanking fire along the barbed wire entanglements or it is used as a bombing post when in close proximity to the enemy’s trenches.
Sometimes a series of combat posts are connected and a new trench established infront of the firing line. This is called the observation line. It is best to avoid this practice as there is always the question whether to hold or abandon this line when the enemy’s attack develops. In either case there are grave disadvantages. If it is held you have a weak line. If you abandon it the enemy can use it for shelter.
Advance posts give excellent service if not too numerous. If there are many of them they are a temptation for hostile raids.
Dimensions of Trenches.These can be found in text-books on the subject. The general idea is that they are to be narrow and deep to prevent observation and to present a small target for high-angle fire.
Loopholes.Loopholes are used in the ordinary life of the trenches for observation and sniping purposes; but against the real attack of the enemy the firing is done over the parapet. If it is necessary to meet the enemy in hand to hand combat the men climb up on the parapet.
Traverses.Traverses are used to localize the effect of shell or grenade explosions, and to prevent enfilade fire.
They are sometimes used in long stretches of boyaux or communicating ditches as emplacements for A. M. R. to enfilade the same if the enemy penetrates the position.
Transversal Lines.Transversal lines are usually constructed between the first and the second lines and between the second and the third lines. They are short stretches of trenches parallel to the front for special purposes: such as disposing of machine guns and trench mortars in depth; bombing posts for rifle and hand grenadiers; depots and observation posts.
Command posts are usually located in such small transversal trenches, a little in rear of the lines they are in command of. For instance, the captain in charge of a support point might be located in a transversal just in rear of the cover trench.
Support Trenches.The second or support line is established at such a distance that the first line is covered by its fire if the latter is captured.
Also the second line should be placed so that it will be out of the zone of dispersion if the first line is the artillery target either of your own or of hostile fire. This places the distance between the two lines at from 150 to 400 yards. At this distance also rifle grenade fire can be used in conjunction with an artillery preparation for a counterattack against the first line.
The organization of the second line is thesame as that of the first; in other words, the same principles and elements of defense are used: making employment of barbed wire, flanking fire, cover trenches, etc.
The second line is the main line of resistance and must be made as nearly impregnable as possible. For this purpose it must be thoroughly and completely organized.
In the support line are the reserves of the C. of R. and for their proper shelter they should have very deep dugouts, and all the requisites for the comfort and rest of the troops.
Redoubts.Behind the support line is a redoubt containing the command post of the battalion commander. It is the last strong point of the center of resistance and is organized for an all-around defense.
The line of redoubts is the last line of serious resistance. If the enemy penetrates this line a breach has been made in the position at this point.
Boyaux and Communicating Ditches.As we have said before trenches for communicating purposes must be dug both in depth and laterally. We shall call those from front to rear boyaux, and those running laterally communicating ditches.
The number of boyaux is not fixed as that ofthe different lines. There must be at least one between each support point and its center of resistance.
Usually boyaux are used for movements in both directions. Often certain boyaux are designated for entrance only and others for evacuation. The numbers of the latter are usually less than the former.
In an attack all boyaux are used for movements from rear to front.
All movements to the rear while reinforcements are being brought up must be executed in the open ground, exceptions being made in the case of wounded.
Boyaux are important for the movement of supplies and ammunition, but above all they are essential for reinforcements during battle. The greater part of the troops in a sector is held in reserve in the second and third lines. This disposition is only possible if you have good boyaux to the front lines.
All boyaux and communicating ditches are narrow and deep. Boyaux are wider between the second and third line than they are between the first and second. Evacuation boyaux are usually wider than others. The trace of a boyau must be such as to prevent enfilade fire.
At intervals of about ten yards turnouts largeenough for a stretcher are constructed in the side of the boyaux for passage of troops in different directions. Boyaux are named and signs are put up similar to those for streets in a city. The same name of a boyau must be kept from the third lines to the first.
At branches of the main boyaux they are dug a little deeper to avoid mistakes of identification.
As was said before certain boyaux are organized for defense.
It may be said here that supplies carried up at night are usually brought along on top of the ground close to the boyaux. This gives freer movement and the carriers are close to the cover of the trench if needed.
Accessory Defense.Of all the accessory defenses such as barricades, abatis, trous-de-loup, etc., the most important by far is barbed wire, which is almost exclusively used for obstacles.
Barbed wire should be placed from twenty to fifty yards in front of the first line. At this distance shelling of the barbed wire belts will do very little damage to the first line.
The wire entanglements must be under fire of the first line.
Command Post for Center of Resistance
The trace of the wire belt is not necessarily parallel to that of the firing line, but should be so placed as to obtain flanking fire along the wire belts. Good entanglements are constructed in double belts, the distance between the two belts being from ten to twenty yards, the farthest belt, of course, being constructed first.
Breaches must be left through the wire entanglements for the passage of patrols, friendly raiding parties, etc. Portable sections of barbed wire are used to close these passages when necessary.
All accessory defenses must be concealed so they cannot be easily observed and destroyed by the enemy.
Command Post.A command post, in the full sense of the word, contains the headquarters of the leader of a division of a sector.
The command post must first of all be a good observation post, after which the other requisites are installed. When the observation post has been constructed the following are built: a room for the headquarters staff to work and to sleep in, a telephone central, dugout for liaison group, and a depot.
The preceding discussion is a development of a position from battle conditions. On the other hand if you are unmolested by theenemy the order of organizing a position would be as follows:
(1) Construct the emplacement to obtain flanking fire.
(2) Construct barbed wire entanglements.
(3) Observatory and dugouts.
(4) Trenches.