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§ 54 to be of maximum service must be capable of action to the full in a downward direction with the greatest angle of fire (both forward and aft, and laterally), that the limitations imposed by structural considerations permit. Similarly, we know that the initial need for armour is mainly to resist attack from below. These facts remain, and cannot be altered by the additional duties imposed when aeroplane attacks aeroplane. We may, and in fact shall, have to provide for a far wider range of fire; we shall need to make provision for training our gun or guns upward as well as downward; likewise we may find it expedient to provide protection against fire from above as well as beneath. But any extended scheme of armament or protection so developed takes essentially as its starting point the more elementary condition.

§ 55. Importance of Upper "Gage" or Berth. The first result of importance arising from the above facts is, in any aeronautical engagement, the importance of the upper berth. The machine which is able to attack from above is acting under the conditions for which its armour and armament were initially provided. Beyond this, the taking of the upper position at the start, or perhaps, we may say, before the start, gives the power to outmanœuvre an enemy, in spite even of inferior speed capacity in the ordinary acceptation of the term. The initial difference in altitude represents a store of potential energy which may be drawn upon when the opportunity occurs; this is, in fact, the principle utilised by the hawk, the kite, and other birds of prey. The objective of securing the upper berth, or position, or "gage," if we adopt the old-time word used by naval writers, will probably prove to be, and will remain, the key or pivot on which every scheme of aeronautical tactics will, in some way or another, be found to hang.