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. HELMETS 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 HELMETS 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. [Illustration: Plate 40a.--Gas helmet.] 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 DESCRIPTION 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. DIRECTIONS FOR USE Remove paper cap from mouthpiece of tube valve. Remove service cap. Pull helmet over head. Adjust so that goggles are over eyes. Tuck in skirt of helmet under coat collar and button coat so as to close in skirt of helmet. Hold the tube lightly in lips or teeth like stem of pipe, so as to be able to breathe in past it and out through it. _Breathe in through mouth and nose, using the air inside the helmet. Breathe out through tube only._ DIRECTIONS FOR CARE OF TUBE HELMET 1. Do not remove the helmet from its waterproof case except to use for protection against gas. 2. Never use your tube helmet for practice or drill. Special helmets are kept in each company for instruction only. Should the goggles become misty during use they can be cleared by rubbing them gently against the forehead.