Among distinguished students of this problem of gun-fire and the aeroplane is Colonel J. E. Capper, who was, for seven years, in charge of the aeronautical work of the British Government. His view is that artillery, however well-trained, would have very great difficulty in firing accurately at a fast-flying machine. 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.