The star shells have been constantly used during the war, and their efficacy has been enormous. But there have been endless other means of illumination, with equally endless variations in the styles of construction. Among the simplest and most useful of these are the illuminating hand grenades. These are of the utmost practical value at night in the effort to repulse wave attacks against intrenchments. When they are thrown in front of an advancing enemy, the light from their combustion renders possible a precise aim in firing, so that shots which would otherwise be wasted in the darkness have a deadly effect. Such grenades are also of much utility to aeronauts in dirigibles and in aeroplanes, since they are available as illuminating agents, whether for purposes of observation or of bombardment.
A distinct class of the illuminating projectile is the tracer bomb, which is directed against both dirigibles and aeroplanes. The difficulty of attacking either the dirigible or aeroplane in the air is due, not only to the great mobility of the objective, but also to the fact that the marksman is un-able to determine precisely wherein lies any inaccuracy of aim. He cannot detect the exact nature of his fault, whether the error be as to height or direction. The conditions of markmanship aloft are radically different from those on the ground, where observation is possible concerning the point at which the projectile falls, and by careful observance one may rectify any error. The tracer bomb solves the difficulty for aerial combat, since it defines a luminous trajectory, by which its failure to reach the mark is clearly indicated, and opportunity is offered for remedying mistake.
This variety of bomb has the ordinary form, but there is an essential variation in the construction. The point is pierced with holes, and the space adjacent within the point is filled with a powerful illuminating powder. The powder is also incendiary. When the projectile is launched, the powder is immediately ignited. Flames from the combustion issue out of the holes in the nose, and thus a luminous light flashes for the whole trajectory of the bomb.
While such tracer bombs may also be incendiary, they are not to be identified with the ordinary incendiary projectiles. The purely incendiary bomb contains a number of cylinders filled with a mixture suited to incendiary purposes. This is a composition in which nitrate of baryta is used with priming powder. The cylinders are equipped with quick fuses. Each cylinder is separately covered with tarred cloth. The interstices about the cylinders are filled with powder.
It must be conceded that, under particular circumstances, fireworks may prove futile when used in an effort for communication. This is not due to any inherent fault in the devices themselves, but is occasioned by some extraordinary difficulty encountered. An illustration is afforded by the experience of a British sector, when the Germans preceded a local offensive by a discharge of fireworks, in which every conceivable variety was employed. The effect of this spectacular medley was a flaming confusion in the heavens, through which nothing could be distinguished with the exactness essential for the reading of signals. When the British front line sent up its summons for the barrage, the artillery watchers were powerless to read the message amid the baffling flames flung forth by the enemy. Often, too, the air becomes charged with dust and smoke overlying the battlefield until it attains a density in which lesser lights vanish utterly, and even the most brilliant radiance becomes powerless to pierce the dun war cloud with its rays.
Nevertheless, this war has shown, as never before, the vital worth of pyrotechnic devices in military operations. Under anything approaching normal conditions, the use of fireworks offers a method of communication that is equally quick and exact. It suffices admirably for messages from the foremost positions to headquarters, or to the artillery stations. It is available for ready communication between sec-tors; between the front line and its advanced posts; between aeronauts aloft and persons on the ground. It has been proven that fireworks often remain a possible means for sending messages when all other methods of communication have been cut off. Since such communication is a prime necessity for successful warfare, the importance of pyro-techny is manifest.
On the entry of the United States into the war, it was decided to adopt the French system of pyrotechny, since the American forces were to operate in a sector held by the French Army, which rendered imperative an identical system of signals. There has been much discussion concerning the respective merits of French and British methods, which differ radically. The French employed a far greater variety of signals, and were even increasing the number of types when the armistice was declared. In spite of this divergence, however, both systems worked very satisfactorily. The American adoption of the French method was due to the circumstances of location, rather than to superior merit as compared with the British scheme.
Four general designs in firework devices were in constant use by both the French and the British armies. These included signal pistols, rifle lights, rockets, and position or ground lights. In a general way the fireworks employed by the Germans were similar to those of the French. But there was an important difference in the method of construction for the signal-pistol cartridge. The German cartridge was lighted on the instant of leaving the pistol. The illumination thus began at the moment of discharge, continuing throughout the trajectory. This effect was sometimes of great value, as, for example, when such a cartridge flared suddenly over no man's land and the raiders, unwarned, had no time even to flatten out on the ground. All the French cartridges were fitted with delay fuses, by which the ignition was effected only when the star reached its limit of height.