An instance which Colonel Capper gives is this: if the range of a gun is 5000 yards, an aeroplane, moving across it at a speed of fifty miles an hour, would be in range for less than 3 1/2 minutes. During this period of 3 1/2 minutes, the gun would need to travel across an angle of 60 degrees, altering its range down to 4330 yards in the first 1 3/4 minutes, and increasing it again to 5000 yards in the next 1 3/4 minutes.
To do this would be an extremely difficult task, even if the aeroplane, while flying past, made itself the easiest possible target; that is to say, if it flew steadily at one level, all the time, and moved directly across in front of the guns. But an airman would, naturally, seek to make himself as difficult a target as possible. He would, therefore, constantly alter his altitude by movements of his elevating plane; and he would, in addition, steer erratically from side to side.
How confusing this would be for the gunner may easily be imagined. Apart from the speed of the aeroplane, which would, as shown, only permit him a brief opportunity of firing at it, he would be faced with the fact that range, elevation, and direction of the elusive target would constantly be altering. In addition, he would probably be called upon to make allowance for a wind, when aiming at the machine.
Apropos the rapidity with which a modern-type machine will come into the range of a gun, and disappear again, an incident in some minor manœuvres held in France is of interest. On this occasion, a special gun, designed to shoot at aircraft, and mounted upon a motor-car, was taken out with the troops. Suddenly, an aeroplane appeared in sight. It was flying straight towards the troops, which were on the march. The special gun was called for; but, before it could be brought into action, and trained upon the aeroplane, the latter had gone completely out of range. This illustration shows what an unsatisfactory and elusive target an aeroplane is bound to be.
II. Shrapnel shell—Question of hitting a vital part of the aeroplane—Difficulty of identifying friend or foe.
It is generally agreed, among artillery experts, that shrapnel shell should form a suitable projectile to be fired against an aeroplane. The shrapnel is, indeed, a particularly-deadly missile. This shell consists of a metal case, containing a sufficient amount of explosive to burst it, when the fuse explodes the charge. This fuse can, of course, be set so that the shell explodes at any given distance from the gun which fires it.
Inside the metal case, or shell, is a charge of bullets. When the shell bursts, these bullets fly out from it, ready to spread destruction over an appreciable area. Should a shell burst in close proximity to an aeroplane, for instance, the scattering charge would, it is anticipated, break struts and stays, and possibly hit the pilot, or some vital part of his machine.
But, granting the deadly nature of a well-aimed shrapnel shell, there are several points to be considered, before we can imagine it bringing an aeroplane to the ground. In the first place, there is the question of the timing of the fuse. This must be done, of course, with absolute accuracy; and the gunner must aim his weapon at a point in front of the aeroplane, as it flies across his view. This represents a matter for nice calculation, being determined by the speed of the aeroplane aimed at, the speed of the shell, and the distance of the aircraft from the gun.
Thus, when he is firing at a sixty-mile-an-hour monoplane, passing swiftly through the air, several thousand feet away, a gunner must obtain his range without delay, set his fuse accurately, and aim his gun with the greatest care. And, all the time, his target will be moving as fast as an express train, and perhaps making erratic twists and turns in the air.
It is not surprising, in view of such circumstances, that one of the greatest of military experts has declared that an aeroplane, flying at sixty miles an hour, and at an altitude of from 3000 to 4000 feet, will present an exceptionally-difficult mark, even to the most skilled of gunners, equipped with special weapons.