Unboxed grenades should be kept covered as far as possible. All safety pins and working parts, especially those made of bra.s.s, should be kept oiled to prevent their setting from corrosion by the gas.

(3) LIGHT TRENCH MORTARS AND THEIR AMMUNITION:

As far as the supply of oil permits, the bore and all bright parts of light trench mortars and their spare parts should be kept permanently oiled. When not in use, mortars should be covered with sacking or similar material.

Unboxed ammunition should be kept covered as far as possible and the bright parts oiled immediately after arrival. Ammunition which has been in store for some time should be used up first.

Sentries must be prepared to give the alarm on the first appearance of gas, as a few seconds delay may involve very serious consequences.

Signals must be pa.s.sed along by all sentries as soon as heard.

The earliest warning of a gas attack is given:

(a) By the noise of the gas escaping from the cylinders.

(b) By the appearance of a cloud of any color over the enemy's trenches. If the attack takes place at night, the cloud will not be visible from a distance.

(c) By the smell of the gas in listening posts.

(1) ACTION TO BE TAKEN IN THE TRENCHES ON GAS ALARM: (a) Respirators to be put on immediately by all ranks (a helmet, if no box respirator is available).

(b) Rouse all men in trenches, dug-outs and mine shafts, warn officers and artillery observation posts and all employed men.

(c) Artillery support to be called for by company commanders by means of prearranged signals.

(d) Warn battalion headquarters and troops in rear.

(e) All ranks stand to arms in the front trenches and elsewhere where the tactical situation demands.

(f) Blanket curtains at entrances to protected shelters to be let down and carefully fixed.

(g) Movement to cease except where necessary.

(2) ACTION TO BE TAKEN IN BILLETS AND BACK AREAS: (a) All men in cellars or houses to be roused.

(b) The blanket curtains of protected collars, etc., to be let down and fixed in position.

(c) Box respirators to be put on immediately, the gas is apparent.

H. Action During a Gas Attack:

(1) PROTECTIVE MEASURES:

There should be as little moving about and talking as possible in the trenches. Men must be made to realize that with the gas now used by the enemy, observance of this may be essential for their safety.

When an attack is in progress, all bodies of troops or transport on the move should halt and all working parties cease work until the gas cloud has pa.s.sed.

If a relief is going on, units should stand fast as far as possible until the gas cloud has pa.s.sed.

Supports and parties bringing up bombs should only be moved up if the tactical situation demands it.

If troops in support or reserve lines of trenches remain in, or go into, dug-outs, they must continue to wear their anti-gas appliances.

Officers and N.C.O's must on no account remove or open up the masks of the box respirators or raise their helmets to give orders. The breathing tube may be removed from the mouth when it is necessary to speak, but it must be replaced.

Men must always be on the look-out to help each other in case an anti-gas device is damaged by fire or accident. When a man is wounded, he must be watched to see that he does not remove his respirator or helmet until he is safely inside a protected shelter; if necessary, his hands should be tied.

Men must be warned that if they are slightly ga.s.sed before adjusting their respirators or helmets they must not remove them. The effect will wear off.

(2) TACTICAL MEASURES:

From the point of view of protection against gas, nothing is gained by men remaining in unprotected dug-outs or by moving to a flank or to the rear. It is, therefore, desirable that on tactical and disciplinary grounds all men in the front line of trenches should be forbidden to do these things. In support or reserve lines where there are protected dug-outs, it is advisable for men to stay in them unless the tactical situation makes it desirable for them to come out.

Nothing is gained by opening rapid rifle fire unless the enemy's infantry attacks. A slow rate of fire from rifles and occasional short bursts of fire from machine guns will lessen the chance of their jamming from the action of the gas and tends to occupy and steady the infantry.

It should be remembered that the enemy's infantry cannot attack while the gas discharge is in progress and is unlikely to do so for an appreciable time--at least 10 minutes--after it has ceased. It is, in fact, a common practice for the enemy infantry to retire to the second and third line of trench whilst gas is being discharged. There is, therefore, no object in opening an intense S.O.S. barrage of artillery on "No man's land" during the actual gas cloud and it is advisable that the warning to the artillery of a gas attack should be a signal differing from the ordinary S.O.S. signal, as the latter may have to be sent later if an infantry attack develops.

It must be remembered that smoke may be used by the enemy at the same time as, or alternately with, the gas and that under cover of a smoke cloud he may send out a.s.saulting or raiding parties. A careful look-out must, therefore, be kept; hostile patrols or raiders may be frustrated by cross-fire of rifles and machine guns and should an a.s.sault develop the ordinary S.O.S. procedure should be carried out.

I. Precautions Against Gas Sh.e.l.ls:

Owing to the small explosion which occurs with these sh.e.l.ls, they are liable to be mistaken for blinds, and even when the gas is smelt men may not realize its possibly dangerous character at once and so may delay putting on respirators or helmets until too late. Men sleeping in dug-outs may be seriously affected unless they are roused. Men in the open air are unlikely to be seriously affected by poison gas sh.e.l.ls, provided they put on respirators or helmets on first experiencing the gas. The following points should therefore be attended to:

(i) All sh.e.l.ls which explode with a small detonation or appear to be blind should be regarded with particular attention; the respirator or helmet should be put on at the first indication of gas and blanket protection of shelters adjusted.

(ii) Arrangements must be made for giving a _Local_ alarm in the event of a sudden and intense bombardment with poison gas sh.e.l.ls, but care must be taken that this alarm is not confused with the main alarm.

Strombos horns must on no account be used to give warning of a gas sh.e.l.l bombardment.

(iii) All shelters in the vicinity of an area bombarded with poison gas sh.e.l.ls must be visited and any sleeping men roused.

(iv.) Box respirators or helmets should continue to be worn throughout the area bombarded with poison gas sh.e.l.ls until the order is given by the local unit Commander for their removal.

Lachrymatory or "tear" sh.e.l.ls are frequently used by the enemy for the purpose of hindering the movements of troops, for preventing the bringing up of supports, or for interfering with the action of artillery. Owing to the deadly nature of poison gas sh.e.l.ls, however, the precautions given in paragraph 60 above, must be taken for all gas sh.e.l.ls. The goggles are intended for use after lachrymatory bombardments only, in cases where the irritant gas persists in the neighborhood.

K. Action Subsequent to a Gas Attack:

1. GENERAL:

The most important measure to be taken after a cloud gas attack is to prepare for a further attack. The enemy frequently sends several successive waves of gas at intervals varying from a few minutes up to several hours and it is therefore necessary to be on the alert to combat this procedure. The following measures should be adopted as soon as the gas cloud has pa.s.sed:

(a) Removal of respirators.--Anti-gas fans should be used to a.s.sist in clearing the trenches of gas, so as to admit of respirators being removed. Respirators and helmets must not be removed until permission has been given by the Company Commander.

A sharp look out must be kept for a repet.i.tion of the gas attack, as long as the wind continues in a dangerous quarter.

2. MOVEMENT:

Owing to the enemy gas sometimes causing bad after effects, which are intensified by subsequent exertion, the following points should be attended to: (a) No man suffering from the effects of gas, however slightly, should be allowed to walk to the dressing station.

(b) The clearing of the trenches and dugouts should not be carried out by men who have been affected by the gas.

(c) After a gas attack, troops in the front trenches should be relieved of all fatigue and carrying work for 24 hours by sending up working parties from companies in rear.

(d) Horses which have been exposed to the gas should not be worked for 24 hours if it can be avoided.

3. CLEARING DUGOUTS AND OTHER SHELTERS:

It is essential that no dugout be entered after a gas attack event with box respirators or helmets adjusted, until it has been ascertained that it is free from gas. The only efficient method of clearing dugouts from gas is by thorough ventilation. The older method of spraying is not efficient.

An appreciable quant.i.ty of gas may be retained in the clothing of men exposed to gas attacks and also in bedding, coats, etc., left in shelters. Precaution should, therefore, be taken to air all clothing.