If any person be inclined to doubt the practical importance of pyrotechny in military operations, let such a skeptic consider the fact that, in the World War, the British troops used position lights at the rate of ten millions a month. When we consider that this quantity was for merely a single sort of firework, while a great number of various other devices were in constant use, and when we consider, further, that the figures are for the requirements of only one nation among the many battling nations, we are compelled to realize the vast and vital significance of the pryotechnic art in modern warfare.
Throughout history, darkness has always been recognized as a supreme hindrance to military operations. The first efforts toward an effective artificial form of illumination that should serve to dispel the obscurity of nighttime, and thus permit some degree of successful belligerent activity, was undertaken by the French in the reign of Louis XIV. To this end, the military experimenters employed powerful rockets equipped with parachute flares, which attained a considerable measure of success. At this same time, also, the British military experts, following a similar line of experimentation, secured almost parallel results. Reference has been made in a previous chapter to the enthusiasm prevalent in this period over the possibilities of pyrotechnic agents in warfare, and it has also been pointed out that this enthusiasm vanished when the increased range of rifles and cannon reduced the flight of any firework to comparative unimportance. Indeed, the reaction was such that the military authorities ignored even the value of devices for purposes of illumination, apart from any use as missiles. So, exact knowledge in this direction, obtained with much difficulty, was first neglected, and then lost.
There was, in fact, no serious revival of the effort toward night illumination as a war measure until 1870. But, during the siege of Paris, the engineer Bazin contrived an electrical lighting post, which was established at the Moulin de la Galette, on the Heights of Montmartre. This light was operated with a fair degree of success. Its shaft had a range of about 10 kilometers. This was sufficient to cover the peninsula of Gennevilliers. The illumination was effective in preventing the Germans from crossing the Seine at this point.
Nevertheless, 30 years elapsed before this matter of night lighting was again taken up. Experiments were conducted year after year, but it was not until 1910 that a specific result was attained. This was an illuminating automobile, which appeared in the maneuvers at Beauce. Its achievement, however, was not notably successful. A primary defect lay in the fact that its power was insufficient. The shaft of light was so narrow that it necessitated constant movement in every direction. The effect was to render observations both difficult and unsatisfactory. Moreover, the slightest obstacle in its path nullified the effect. It was wholly at the mercy of any irregularity in the terrain, or any interference by walls or buildings. The removal of the apparatus to an elevated site, in order to overcome such obstacles, was a dangerous expedient, since the light thus immediately became the target of hostile projectiles, a prey to quick destruction.
But, already, the evident difficulties in the way of electrical lighting had led the French authorities to consider a revival of the old methods of illumination through the use of rocket devices. The pyrotechnic school at Bourges busied itself with the problem, but found many difficulties in the way. The skill displayed by the artificers centuries before, under the monarchy, had been forgotten, and its restoration was a tedious task. It was not until near the end of 1901 that the long-continued research produced an illuminating apparatus approximately satisfactory. But, once a start had been made, progress was swift and sure, and its end was triumphant.
Naturally, the German staff, in its avid preparations for combat, did not neglect a means of such importance. The Krupp works developed a projectile, which appeared in 1913 under the name of searchlight shell. In its essentials, this is the star shell made familiar to the world in the war. It contains within the shell a number of small cylinders, called stars, loaded with the illuminating composition. The mixture used is similar to that in white Bengal lights; but threads or ribbons of magnesium may be substituted. The usual number of tubes is six. A very small folded parachute of silk is placed in the bottom of each tube, to support it when cast out of the shell. . . . The French have constructed a similar projectile, containing eight cylinders, which is fired from the short 155 gun.
The shell of the Krupp firework contains a very light charge of powder. This serves two purposes: to kindle the composition in the star cylinders and to throw out the base of the shell, which is held in place only by a weak resistant thread, and, along with this, the tubes. As each cylinder thus issues from out the shell, its parachute is released by the extension of a small lock spring. The parachute is fitted also with a spring that causes the silk to spread open instantly. The cylinder, on dropping, immediately assumes its required position under the parachute, with the burning end downward. The combustion of the illuminating material continues for a period that varies from 45 seconds to several minutes, according to the particular model. The star projects a vivid light toward the ground in the form of a huge cone.
The powder charge of the shell in the German firework is ignited when the projectile has reached the proper point in its flight, by means of a mechanical time fuse, or clockwork movement. The French preference, however, is for a time fuse using a powder train.
It has been found that the most advantageous height for the explosion is 300 meters.
A more recent variation of the luminous projectile manufactured at the Krupp works substitutes for the star cylinders a six-sided prism, which carries the combustion material. This shape leaves a smaller amount of space unoccupied within the shell. Moreover, the prism itself is completely filled with the composition, while the stars were only partly filled. In the old construction, the folded parachute occupied the upper half of each tube. In the new construction, a totally different parachute method is employed. Instead of individual support for each separate cylinder, the parachute is a single one for the whole prism. It is formed from six plates, which have the office of supporting planes. One end of each plate is attached by a hinge to the upper part of the prism. This plane exactly corresponds to a face of the prism, and folds down flat over the face. Thus, when the prism is inserted within the shell, the six plates take up almost no room, as they lie flat against the sides of the prism. But, with the expulsion of the prism from the shell, when the powder charge is exploded, a spring instantly sets them at right angles to the faces of the prism. The resistance of the plates has the effect of a parachute, and the descent of the prism is sufficiently retarded. By means of this device, the economy of space is such that a light of greater intensity, or of longer duration, is secured. This form of projectile, as thrown by cannon, has also been adapted for use with rifles and special pistols, and with carbines of large caliber.