Page:Aircraft in Warfare (1916).djvu/70

§ 15 is an important factor, this being mainly dependent upon the wind and weather. Under favourable conditions an expert shot using the Lewis gun has delivered the whole contents of a magazine (of 47 cartridges capacity) into an area 10 ft, by 60 ft, from an altitude of 600 ft, at a range of 1,000 yards. Making allowance for this expert handling of the weapon, as being superior to the average ability available under service conditions, there can be no doubt as to the deadly efficiency of a gun of the Lewis type as an aeroplane armament. The author has himself witnessed a performance very little inferior to the above in weather that could by no means be considered ideal. Apart from many detail points of merit, the Lewis gun for aeroplane service, has many advantages; firstly, on account of its self-contained magazine, which, by the abolition of the cartridge-belt, etc., permits of the gun being trained freely in any direction from vertically upwards to vertically downwards; secondly, its light weight, which also allows of its use as a shoulder-arm; and, thirdly, the adoption of direct air cooling in place of the usual water-jacket.

Assuming the proved accuracy of the Lewis gun as the criterion of machine-gun fire, it is evident that an estimate of the effectiveness of low-altitude aeroplane attack becomes little more than a matter of simple arithmetic. We may take, for example, the problem to be that of executing a counter-attack upon infantry, themselves attacking a position in open order, the counter-attack to be delivered against the foremost line, lying prone at two or three paces interval. We are justified in assuming that the magazines will be emptied over an area defined as a belt of 10 ft, or 12 ft, width, in which, therefore, there is one man to approximately 100 sq. ft, of ground under fire. Now the area of target