=Cloud Gas.= The Americans at once concluded that since cloud gas attacks were so effective, efforts should be made to make these attacks of frequent occurrence by decreasing the weight of the cylinders, and by increasing the portability and methods of discharging the cylinders. As early as March, 1918, specifications for cylinders weighing not more than 65 pounds, filled and completely equipped for firing, were cabled to the United States. They would have been used in large numbers in the campaign of 1919 had the enemy not quit when he did. Toxic smoke candles that are filled with solids driven off by heat will probably be the actual method in the future for putting off cloud attacks. The toxic smoke candle is perfectly safe under all conditions and can be made in any size desired. Cloud gas attacks will be common in the future, and all plans of defense must be made accordingly. They will usually be made at night, when, due to fatigue and the natural sleepiness which comes at that time, men are careless, lose their way, or neglect their masks, and are thus caught unprepared. Experience in the war proved that a wave attack always produced casualties even, as several times occurred, when the enemy or the Allied troops knew some hours beforehand that the attack was coming. The English estimated these casualties to be 10 or 11 per cent of the troops exposed. =Livens’ Projectors.= The second most effective weapon for using gas by gas troops was and will be the Livens’ projector. This projector is nothing less than the simplest form of mortar, consisting of a straight drawn steel tube and a steel base plate. As used during the World War by the Allies it did not even have a firing pin or other mechanism in the base, the electric wires for firing passing out through the muzzle and alongside the drum or projectile which was small enough to permit that method of firing. These were set by the hundreds, very close behind or even in front of the front line trenches. They were all fired at the same instant, or as nearly at the same instant as watches could be synchronized, and firing batteries operated. As discussed on page 18 these mortars were emplaced deep enough in the ground to bring their muzzles practically level with the surface. It usually took several days to prepare the attack, and consequently allowed an opportunity for the enemy to detect the work by aeroplane photographs or by raids, and destroy the emplacements by artillery fire. It should be added, however, that notwithstanding this apparent great difficulty, very few attacks were broken up in that way. Nevertheless, in line with the general policy of the American troops to get away from anything that savored of trench warfare, and to make the fighting as nearly continuous as possible with every means available, the American Chemical Warfare Service set at work at once to develop an easy method of making projector attacks.