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Rh destruction it is required to encompass, both in the matter of speed and climbing capacity. Thus it will require to possess a considerable superiority in the essential matter of horse-power; it must be made impossible for its prey to escape either by horizontal flight or by putting on altitude.

§ 93. Tactical Importance of Altitude. This question of altitude is one of really vital consequence in connection with the tactics of the air. The service machine designed to fulfill the primary function of the Arm must evidently carry its protective plating or armour distributed in such manner as best to resist gun-fire from below. Also the armament is necessarily directed mainly to the downward projection of missiles, by gun-fire or otherwise. Hence to obtain the "upper berth" in an air-fleet action is at the outset to secure a great tactical advantage. It might be supposed that these considerations will lead to an increase in the protection accorded—that is to say, that the service fighting-machine will be fitted with a complete panoply of steel plate, above as well as below. This, however, is improbable, since any such measure would, by reason of the additional weight, so reduce the general mobility of the machine as to constitute too serious a handicap. It would appear to be only possible to ameliorate the conditions under which a machine will have to fight when resisting an attack from above by arranging the gun armament with as great a capacity for upward fire as possible. A further advantage in the possession of the upper berth or "gage" lies in the fact that the potential energy, represented by the difference of altitude, may, at any time, be used to augment the velocity of flight