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Rh launched from a gun or pneumatic projector of some kind, and carrying a charge of explosive and an impact fuse actuated by the striking of the aerofoil member on some part of the enemy's craft. Again, we are confronted with the fact that any such weapon would be of little service apart from attack on an airship, and so may be looked upon as useless lumber.

§ 68. The Supremacy of the Gun. The real fact at the bottom of the whole question is the vital importance of high velocity in any projectile directed against a rapidly moving target, and its doubly vital importance when the craft from which it is projected is also in rapid motion. This is universally recognised wherever the gun is to be found, and it is nowhere more important than in the attack on aircraft by aircraft, and in particular aeroplane on aeroplane. Any lapse of time whilst the projectile is in its flight introduces a corresponding uncertainty owing to the relative difference of motion between gun and mark. Thus a projectile travelling at 200 ft, or 300 ft, per second, such as a rocket or aerial torpedo, would require to be directed at a point so far removed from the aircraft it is intended to hit, that, in the case of an aeroplane, the chances of success would be remote in the extreme.

In brief, nothing but gun-fire gives the necessary rapidity to ensure a reasonable degree of accuracy and useful percentage of hits, and it is probable that for some time to come the demand will be for higher and higher velocity in order that the effective range may be increased. This, however, is looking into the future; at present, the problem of mounting a gun in a satisfactory manner, and getting the highest possible rate of discharge—i.e., rounds per minute—are the more immediate concern of the aeroplane constructor. The relation of the ordinary flight velocity to the mean