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Rh § 56. On Protection against Attack from Above. The question of employing armour as a protection against attack from above, or against dropping fire, is one which requires consideration on an entirely different basis from that of attack from below. In the latter case, the employment of protection in some degree may be looked upon as essential. The steel employed may be thin and only sufficient to be effective above some prearranged altitude, but, nevertheless, it will be essential. Protection from attack by other aeroplanes, or, more broadly, aircraft, is another question; we may express the utility of armour under these conditions definitely in terms of gun-power.

To make this clear let us consider two machines in combat—an aeroplane duel, in fact—and we will take it that at their average distance apart or range the mean number of shots fired by either to score a decisive hit is found to be 600. Now if either aeronaut by the employment of armour or gun-shields, or equivalent device, can reduce the effective target offered by his machine to one-half that previously presented, it will on an average take 1,200 shots to knock him out in lieu of 600 without protection. But in order to provide for the weight of his armour he must cut down his armament; he must sacrifice either his gun weight, and with it his speed of fire, or he must carry a lesser total weight of ammunition, and risk finding himself without means of attack, this being virtually synonymous to being without means of defence. If the only alternative were the cutting down of the speed of fire—tersely, if he were to substitute, say, 30 lb, of armour for 30 lb, of gun—and if this represent half his total gun capacity, and involve a reduction in his speed of fire by nearly one-half, then the change might be considered as nearly justified, since he would receive two shots for every one he could discharge, but would at the same time be proportionately less vulnerable.