=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 a.s.sault 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.

[Ill.u.s.tration: Fig. 19

Wire Cheveaux de Frise]

[Ill.u.s.tration: Fig. 20

Wire Cheveaux de Frise]

=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 a.s.sault 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.

CHAPTER XII

TRENCH AND MINE WARFARE[14]

=1194. Asphyxiating gases.= The asphyxiating gases employed may be divided into three general cla.s.ses, viz:

_Suffocating gases_, the most common of which are carbonic and nitrogen.

_Poisonous gases_, under which head come carbon monoxide and cyanogen.

_Gases which affect the throat and bronchial tubes_, such as chlorine and bromine. The latter cla.s.s is most commonly employed.

The methods usually employed for liberating these gases are to have a plant some distance in rear of the trenches where the gas is stored under pressure and carried to the trenches through pipes, where it can be liberated towards the enemy's trenches when there is a favorable wind to carry it along; or, the gas may be carried in cylinders or other containers and liberated at the desired points. Hand grenades or bombs are also employed which, upon bursting, liberate the gas or in some cases scatter acids or caustic soda. Some of these bombs contain a chemical which when liberated affects the eyes, causing impaired vision. The Germans employ several kinds of sh.e.l.l containing gases of different densities, one of heavy gas fired as a curtain to the rear to permit reinforcement of the trenches and another of lighter gas to demolish the trenches and destroy the firing line. As a general rule these gases are employed when the fire trenches of the opposing forces are close together though the sh.e.l.l containers may be used at long ranges. All of these gases being heavier than air lie close to the ground and flow over and down into the trenches.

=1195. Protection against gases.= The best protection against these gases, is a mask of some kind. The commonest form employed is a flexible mask that conforms to the head, is fitted with gla.s.s for seeing through, and has an arrangement of tubes and valves which require the wearer to inhale through his nose and exhale through his mouth.

These masks have an absorbent composed of hyposulphite of sodium or of 72 per cent of the nitrous thiosulphate and 28 per cent of bicarbonate of soda. This absorbent placed so that air must be breathed through it, neutralizes the acids in the gases. Soldiers are provided with these masks, sometimes with two of them, and are required to have them renewed every three months.

Trench sprays may be used to spray neutralizing liquid in the trenches to kill the gases.

The _favorable conditions_ for the employment of gases are wind blowing toward the enemy's trenches and warm weather. _Unfavorable conditions_ are rain, cold, and adverse winds.

In some localities weather vanes placed in the direction of the enemy's trenches and arranged so that they may be watched at night give an indication of favorable winds and enable the defender to prepare for a gas attack.

Before the masks were provided bonfires were prepared of oil soaked materials which; when ignited, produced an intense heat and the resulting column of air diverted the gas clouds.

=1196. Liquid fire.= By use of hand or motor driven pumps, and a light grade of petroleum, columns of liquid fire may be squirted into the opposing trenches. If the oil should fail to remain lighted it may be fired by bursting hand grenades or throwing fire b.a.l.l.s into the trenches. This means of attack is employed when opposing trenches are close together.

As a defense measure ditches may be dug in front of the trenches and filled with a porous material which is then soaked with oil. Heavy oils, being hard to ignite, are not dangerous to the defense, and will remain with little loss for a long time. To make sure of prompt ignition gas lines are laid in the ditches. When turned on the gas readily ignites and the resulting fire produces great heat. Wire or barbed wire looped in the ditches and staked down makes this a formidable obstacle.

=1197. Grenades and bombs= are containers, designed to be thrown by hand, by a sling, fired as a rocket or from specially constructed mortars, or dropped from aerial craft. They burst by time or percussion fuses and may be improvised in a variety of forms and are most useful in close attack or defense. Their effect is local but they are very demoralizing to men's nerves.

=1198. Hand grenades= are designed to be thrown by the hand and vary greatly in construction. In general, however, they consist of a container filled with bullets or pieces of iron or other metal in the center of which is a charge of high explosive which scatters the bullets or fragments with deadly effect. The three methods of discharging a hand grenade are:

_By time fuse_ which is lighted by hand. About 5 to 9 seconds is the time from ignition until the grenade bursts. This does not give the defender time to pick up the bomb and throw it out of the trench.

_By friction primer and fuse._ In this form of hand grenade a strap on the wrist with a short line attached with a hook on the end of it serves, when the hook is engaged in the ring of the grenade, to jerk the primer when the grenade is thrown. This automatically ignites the fuse which bursts the grenade in from 4 to 5 seconds.

_By percussion._ In this form of grenade the charge is fired when the grenade strikes the ground or object at which it is thrown. In this form of grenade a safety pin holds the plunger from the cap. When the grenade is to be thrown the safety pin is withdrawn.

As a general rule fuse burns at the rate of 1 inch in 1 and 1/4 seconds; however each lot of fuse should be tested.

Figs. 1 and 2 show two forms of improvised grenades. Common cans, such as preserved fruits and vegetables are shipped in commercially, make good containers. The usual weight of a hand grenade is about 1-1/2 pounds.

[Ill.u.s.tration: Fig. 1

Hair Brush Bomb]

[Ill.u.s.tration: Fig. 2

Hand Grenade]

=1199. Other methods of throwing grenades.= Many grenades have been designed to be fired from the ordinary rifle. This grenade has a rod which is inserted in the barrel of the rifle. A special charge of powder is used in the cartridge from which the bullet has been withdrawn.

Common slings, catapults, and other devises have been frequently used.

=1200. Aerial mines.= (Fig. 3.) This form of grenade is very heavy, often weighing 200 pounds and is fired from a trench mortar.

[Ill.u.s.tration: Fig. 3

_Aerial Mine_]

=1201. Winged torpedo.= (Fig. 4.) This projectile is fitted with three winged vanes which steady its flight and greatly increase the accuracy. A rod fitted into its base enables it to be fired from a comparatively small trench, mortar. The torpedo weighs about 40 pounds and the mortar 200 pounds. The mortar, being light, can be carried from one part of the trench to another by two men.

[Ill.u.s.tration: Fig. 4

_Winged Torpedo_]

The aerial mine and winged torpedo may be used effectively to beat down the enemy's defenses, destroying his sand bags and trenches, and cutting away wire entanglements and other obstacles. The winged torpedo having a greater range (500 yards) and being more accurate, is the more effective.

=1202. Bombs from air-craft= are some form of high explosive bomb which burst on striking. Another type of bomb used by aeroplanes consists of a container filled with steel darts. The bursting charge is fired by a fuse. The operator usually cuts the fuse so that the bomb will burst at a considerable alt.i.tude. The steel darts are scattered in all directions and have sufficient velocity to pa.s.s through a man or horse.

=1203. Protection against hand grenades.= (Fig. 5.) For protection against hand grenades and bombs a screen of wire netting may be erected in front of the trenches and arranged at such a slope that most of the grenades pa.s.sing over the screen will clear the trench while those striking the netting will roll away from the trench. This protection is very satisfactory for communications, machine gun emplacements, etc., but, is of doubtful value in fire trenches as it does not permit an easy offensive by the defenders.