Chapter 45

OBSTACLES

=1173. Object.= The main objects in placing obstacles in front of the trenches are, to protect them from surprise, and to stop the enemy's advance or to delay him while under the defender's fire.

=1174. Necessity for obstacles.= It is evident that the present tendency is to reduce the number of men assigned to constant occupancy of the first line trenches. This is due to the effectiveness of rifle fire at close range, the destructive effect of shell and shrapnel, the infrequency of daylight attack on intrenched positions, and the severe strain on the men. The aim seems to be the placing here and there of a lookout or trench guards, who, when necessity demands can call help from the near by splinterproofs, dugouts, etc., before the enemy can make his way through the obstacles. It has been found from experience in the European war that as long as shells are directed at the trenches no danger of attack is feared but, when the shells are concentrated against the obstacles the trenches are manned and preparations are made to resist an assault.

=1175. Location.= Obstacles must be so located that they will be exposed to the defenders' fire, and should be sheltered as far as possible from the enemy's artillery fire. They should be difficult to remove or destroy, should afford no cover for the enemy, and should not obstruct counter attacks. No obstacle should be more than 100 yards from the defender's trench. Care must be taken not to place them so close to the trench that hand grenades can be thrown into the trench from beyond the obstacle. Obstacles may be placed in one, two or three lines. As far as possible they should be concealed so that they will not betray the location of the trench.

=1176. Kinds of Obstacles.= The following are the most common kinds of obstacles:--

=Abatis= consisting of trees lying parallel to each other with the branches pointing in the general direction of approach and interlaced. All leaves and small twigs should be removed and the stiff ends of branches pointed.

Abatis on open ground is most conveniently made of branches about 15 feet long. The branches are staked or tied down and the butts anchored by covering them with earth. Barbed wire may be interlaced among the branches. Successive rows are placed, the branches of one extending over the trunks of the one in front, so as to make the abatis 5 feet high and as wide as desired. It is better to place the abatis in a natural depression or a ditch, for concealment and protection from fire. If exposed to artillery, an abatis must be protected either as above or else by raising a glacis in front of it. Fig. 1 shows a typical form of abatis with a glacis in front. An abatis formed by felling trees toward the enemy, leaving the butt hanging to the stump, the branches prepared as before, is called =a slashing=, Fig. 2. It gives cover, and should be well flanked.

=1177. A palisade= is a man-tight fence of posts. Round poles 4 to 6 inches in diameter at the large end are best. If the sticks run 5 to 8 inches, they may be split. If defended from the rear, palisades give some shelter from fire and the openings should be made as large as possible without letting men through. If defended from the flank, they may be closer, say 3 to 4 inches apart. The top should be pointed. A strand or two of barbed wire run along the top and stapled to each post is a valuable addition.

Palisading is best made up in panels of 6 or 8 feet length, connected by a waling piece, preferably of plank, otherwise of split stuff. If the tops are free, two wales should be used, both underground. If the tops are connected by wires, one will do.

Palisades should be planted to incline slightly to the front. As little earth should be disturbed in digging as possible, and one side of the trench should be kept in the desired plane of the palisade. If stones can be had to fit between the posts and the top of the trench, they will increase the stiffness of the structure and save time in ramming, or a small log may be laid in the trench along the outside of the posts. Figs. 3 and 4 show the construction and placing of palisades.

=1178. A fraise= is a palisade horizontal, or nearly so, projecting from the scarp or counterscarp. A modern and better form consists of supports at 3 or 4 feet interval, connected by barbed wire, forming a horizontal wire fence. Fig. 5.

=1179. Cheveaux de frise= are obstacles of the form shown in Fig. 6. They are usually made in sections of manageable length chained together at the ends. They are most useful in closing roads or other narrow passages, as they can be quickly opened for friendly troops. The lances may be of iron instead of wood and rectangular instead of round; the axial beam may be solid or composite. Figs. 8 and 9 show methods of constructing cheveaux de frise with dimension stuff.

=1180. A formidable obstacle against cavalry= consists of railroad ties planted at intervals of 10 feet with the tops 4-1/2 feet above the ground, and connected by a line of rails spiked securely to each, Fig. 7. The rail ends should be connected by fish plates and bolted, with the ends of the bolts riveted down on the ends.

Figs. 10 and 11 show forms of heavy obstacles employed in Manchuria by the Russians and Japanese, respectively. The former is composed of timber trestles, made in rear and carried out at night. The latter appears to have been planted in place.

=1181. A wire entanglement= is composed of stakes driven in the ground and connected by wire, barbed is the best, passing horizontally or diagonally, or both. The stakes are roughly in rectangular or quincunx order, but slight irregularities, both of position and height should be introduced.

In the =high entanglement= the stakes average 4 feet from the ground, and the wiring is horizontal and diagonal, Fig. 12.

=The low wire entanglement= has stakes averaging 18 inches above the ground and the wire is horizontal only. This form is especially effective if concealed in high grass. In both kinds the wires should be wound around the stakes and stapled and passed loosely from one stake to the next. When two or more wires cross they should be tied together. Barbed wire is more difficult to string but better when done. The most practicable form results from the use of barbed wire for the horizontal strands and smooth wire for the rest.

This is the most generally, useful of all obstacles because of the rapidity of construction, the difficulty of removal, the comparatively slight injury from artillery fire, and its independence of local material supplies.

=1182. Time and materials.= One man can make 10 sq. yds. of low and 3 sq. yds. of high entanglement per hour. The low form requires 10 feet of wire per sq. yd. and the high 30 feet. No. 14 is a suitable size. The smooth wire runs 58.9 ft. to the lb. A 100-lb. coil will make 600 sq. yds. of low or 200 sq. yds. of high entanglement. If barbed wire is used, the weight will be about 2-1/2 times as much.

=1183. Wire fence.= An ordinary barbed-wire fence is a considerable obstacle if well swept by fire. It becomes more formidable if a ditch is dug on one or both sides to obstruct the passage of wheels after the fence has been cut. The fence is much more difficult to get through if provided with an apron on one or both sides, inclined at an angle of about 45 deg., as indicated in Figs. 13 and 14. This form was much used in South Africa for connecting lines between blockhouses. When used in this way the lines of fence may be 300 to 600 yds. long, in plan like a worm fence, with the blockhouse at the reentrant angles. Fixed rests for rifles, giving them the proper aim to enfilade the fence, were prepared at the blockhouses for use at night.

Such a fence may be arranged in many ways to give an automatic alarm either mechanically or electrically. The mechanical forms mostly depend on one or more single wires which are smooth, and are tightly stretched through staples on the posts which hold them loosely, permitting them to slip when cut and drop a counterweight at the blockhouse, which in falling explodes a cap or pulls the trigger of a rifle.

=1184. Military pits= or =trous de loup= are excavations in the shape of an inverted cone or pyramid, with a pointed stake in the bottom. They should not be so deep as to afford cover to the skirmisher. Two and one-half feet or less is a suitable depth. Fig. 15 shows a plan and section of such pits.

They are usually dug in 3 or 5 rows and the earth thrown to the front to form a glacis. The rear row is dug first and then the next in front, and so on, so that no earth is cast over the finished pits.

An excellent arrangement is to dig the pits in a checkerboard plan, leaving alternate squares and placing a stake in each of them to form a wire entanglement, Fig. 16. One man can make 5 pits on a 2-hour relief.

=1185. Miscellaneous barricades.= Anything rigid in form and movable may be used to give cover from view and fire and to obstruct the advance of an assailant. Boxes, bales and sacks of goods, furniture, books, etc., have been so used. The principles above stated for other obstacles should be followed, so far as the character of the materials will permit. The rest ingenuity must supply. Such devices are usually called barricades and are useful in blocking the streets of towns and cities.

=1186. Inundations.= Backing up the water of a stream so that it overflows a considerable area forms a good obstacle even though of fordable depth. If shallow, the difficulty of fording may be increased by irregular holes or ditches dug before the water comes up or by driving stakes or making entanglements. Fords have frequently been obstructed by ordinary harrows laid on the bottom with the teeth up.

The unusual natural conditions necessary to a successful inundation and the extent and character of the work required to construct the dams make this defense of exceptional use. It may be attempted with advantage when the drainage of a considerable flat area passes through a restricted opening, as a natural gorge, a culvert, or a bridge.

Open cribs filled with stones, or tighter ones with gravel or earth may form the basis of the obstruction to the flow of water. The usual method of tightening cracks or spaces between cribs is by throwing in earth or alternate layers of straw, hay, grass, earth, or sacks of clay. Unless the flow is enough to allow considerable leakage, the operation will not be practicable with field resources.

When the local conditions permit water to be run into the ditch of a parapet it should always be done.

=1187. Obstacles in front of outguards= should be low so they cannot be seen at night. A very simple and effective obstacle can be made by fastening a single strand of wire to the top of stout stakes about a foot high, and then placing another wire a little higher and parallel to, and about one yard in rear of, the first. The wires must be drawn tight, and securely fastened, and the stakes fairly close together, so that if the wire is cut between any two stakes the remainder will not be cut loose. Any one approaching the enemy will trip over the first wire, and before he can recover himself he will be brought down by the second. In the absence of wire, small sapplings may be used instead. Of course, they are not as good as wire, but it does not take much to trip up a man in the dark.

Lessons from the European War

What follows is based on reports from the battle fronts in Europe.

=1188. Wire entanglements.= The war in Europe has proven that the wire entanglements are the most important and effective obstacle yet devised. Owing to the intensity of the opposing fire and in many cases to the short distance between the opposing trenches, it has become necessary to construct all forms of obstacles in portable sections which are carried or rolled quickly into place, either by soldiers rushing out in day light and quickly staking the obstacles down or by placing the obstacles quietly at night.

For placing wire entanglements at night, an iron post has been devised about 1/4 of an inch in diameter, with eyelets for attaching the wire. The lower 18 inches is made as an auger, so that the posts can be quietly screwed into the ground at night and the wire attached. Another method of placing wire entanglements is to make them in sections and roll them up. These sections are usually about 20 feet long, the wire firmly fastened to the sharpened stakes. At a favorable moment the soldiers rush out, unrolling the sections as they go and with mauls quickly drive the stakes. Loose ends of wire enable the sections to be bound together as placed.

Another form of wire entanglement is shown in (Fig. 18). Triangular pyramids 3 feet 6 inches high are made of poles or timber. The pyramids are usually arranged in pairs with the wire on three faces so that, no matter if the obstacle is rolled over, a wire fence is presented. These obstacles are carried out and placed so as to break joints and are staked down as soon as possible.

The wire used for entanglements is found more convenient to handle when wound on a stake a yard in length, in a sort of figure eight winding. Special barbed wire of heavier material and barbs placed close together has been found much more effective than the commercial barbed wire.

In some localities electrified wire has been used. In such cases the obstacle is charged in sections, so that, if one section is grounded it will not affect the others.

=1189. Wire cheveaux de frise.= Two forms of this obstacle have appeared. Both are portable. They consist of two or more wooden crosses fastened at their centers to a long pole and connected with each other by barbed wire. This obstacle retains its effectiveness when rolled over. (Figs. 19 and 20) give an idea of their construction. The form shown in (Fig. 19) is often made small enough for individuals to carry. These are prepared in the trenches and used for throwing into one's own entanglements to make them more complex or may be carried when making an assault and thrown into the enemy's trenches to prevent movements from one part of the trench to another. The long stick projects out of the end to be used as a handle.

=1190. Guarding obstacles.= It has been found necessary to keep a constant watch over obstacles after they have been placed.

=1191. Listening posts.= One of the best methods is to post one or more men in listening posts in or beyond the line of obstacles. These listening posts are rifle pits with over head cover, fully protected from fire from the rear as well as front, and loop holes for observation and fire. They are connected with the fire trenches by means of a covered communication or even tunnels in some cases and are provided with some form of prompt communication with the firing trenches by telephone, bell or other means. The communicating trench or tunnel is provided with a strong door which may be closed to prevent an enemy from securing access to the fire trench, in case the lookout is surprised. Pits with trap doors are also used to prevent an enemy from creeping up the tunnel to the fire trench.

These lookouts can give early warning of the approach of an enemy, either for the purpose of assault or cutting through the obstacles. In many instances they have detected mining operations of the enemy by hearing the blows of picks under ground.

=1192. Automatic alarms.= Many automatic alarms have been used to give warning of attack on the obstacles. These vary from the simple setting of a pistol or rifle, which is fired when the enemy attempts to cut through the entanglement, to intricate electrical alarms.

=1193. Searchlights.= Searchlights have been provided so that, the instant an alarm is given the obstacles are flooded by a brilliant light and the enemy exposed to fire.