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Rh offered by a man prone is approximately 5 sq. ft., so that, as an average, one bullet in twenty will find its mark. This represents a man knocked out for every 10 oz, of lead expended, which must be regarded as extremely economical, in view of the fact, that it is usually supposed to take a hundredweight of lead to kill one man, say 30 lb, or 40 lb, for every man put out of action.

§ 16. Points in Favour of Extreme Low-Altitude. In any such work as the foregoing, the question of lowness of altitude is of vital importance. Since no attempt to aim at an individual mark is contemplated, there is no disadvantage from the point of view of the gunner in flying quite low. His target may appear as blurred as the side of a railway cutting viewed from the window of an express train, but so long as he "delivers the goods" within the belt of ground intended, his average hits will not be detrimentally affected. If he is shot at by the infantry line he is attacking, or by a supporting line (usually 300 yards, more or less, in the rear), every man attacking him breaks his cover, and becomes a prominent mark for the defending infantry force. Beyond this, the aeroplane carries armour and presents a comparatively small vulnerable target. The advantage of extreme low-altitude flying in the present connection lies in the fact that it is, in effect, a perfect defence against attack by long-range fire. No matter what developments may be made in air-defence artillery—even if means should be found to render an 18-pounder as handy as a sportsman's shot-gun—if the attacking aeroplane fly low enough, the enemy cannot bring long-range fire to bear without bringing his own infantry lines under fire at the same time.

§ 17. The Future of the Fighting Type of Aeroplane. A reservation has already been made to the