In this method the gas dissemination is effected by means of shells or bombs being fired into the enemy’s trenches containing the desired substances which are released and give off irritant fumes on explosion. The grenades used weigh about 1 pound. They are similar in appearance to the ordinary tin can grenade. Their effect in a trench will continue for 20 to 30 minutes. In the attack a large number should be concentrated in a particular area to produce a large volume of gas. They are thrown by hand, trench mortar or catapult.
Surprise must be guarded against in every possible way. The direction of the wind must be continually watched, and when its velocity and direction are specially favorable the protective measures must be kept ready for instant use and special observers posted. Previous to an attack the enemy may remain comparatively quiet for several days. Noises like the moving of sheet iron may be heard. Preparations may be observed along the position. When the attack starts a hissing noise is heard; this latter is one of the indications that may be evident at night.
Each man on duty in the trenches is provided with two smoke helmets, specially devised and constructed so as to absorb the gas and neutralize its effect, and which if properly cared for and used will provide complete protection from any substance likely to be used by the enemy. They are fitted with a valve tube through which to breathe and with goggles to see through. There are certain rules prescribed for their care and use.
1. They must not be removed from the protective covering except for actual use against an attack.
2. When the helmet has been used once it should be replaced by a new one.
Dummy gas helmets will be provided in each organization by which the men may be practiced in putting them on. The men must be thoroughly drilled in the methods to be employed.
The following directions accompany the helmets issued to the British Army. When our helmets are issued it is probable that each will be accompanied by a complete set of rules for its use and full instructions for the method of getting into it and for its care and preservation.
Direction for Use and Care of Tube Helmets
These helmets are the same as the smoke helmet already issued, except that stronger chemicals are added and a tube valve provided through which to breathe out. The tube valve makes the helmet cooler and saves chemicals from being affected by the breath. The wearer cannot breathe _in_ through the tube valve; this is intended for breathing _out_ only.