5. Allowance for Side and Oblique Winds (see also Sec. 20, Aiming-Off).—(i) No fixed rules can be laid down as to the degree of allowance to be made by aiming-off for side and oblique winds of varying direction and velocity. Owing to the increased time during which the bullet is exposed to the effect of wind, and owing to the height attained in its flight, the allowance for wind at long ranges must be out of all proportion greater to that necessary at close range.
(ii) At close range, whether fire is distributed along the dense line of an infantry attack or concentrated on narrow-fronted attacking columns, the effect of side wind will cause little, if any, loss of fire effect. Individual soldiers, however, in taking the deliberate aim necessary for fire effect, should aim off for side winds of different velocity (see Sec. 20, para. 3).
(iii) In directing fire beyond close range, fire-unit commanders must use their judgment in allowing for deflection due to side and oblique winds by including directions for aiming-off in fire orders. The extent of the allowance will in every case depend upon a variety of factors, including the direction and velocity of the wind and the distance of the target. Neglect to make due allowance for strong winds at longer ranges may lead to loss of fire effect, more particularly in the case of concentrated fire aimed at narrow-fronted targets, such as a machine-gun.
6. Effect of Light.—In bad light, the foresight is less distinctly seen than in good light, and more of it is unconsciously taken into the line of sight. For practical purposes, the effect of light may be disregarded in firing at all ranges.
Section 11.—Need for Collective Fire.
1. (i) Only exceptional targets and very favourable atmospheric conditions will justify soldiers in opening individual fire at distances beyond about 600 yards. Collective fire is necessary to give reasonable assurance of fire effect beyond about 600 yards up to about 1,400 yards, which is usually the limit of effective rifle fire. Beyond 1,400 yards, the fire of even large and well-controlled units of infantry has seldom much effect upon the decision of the struggle for superiority of fire.
(ii) Collective concentrated fire is also used to form a cone of fire for observation of fire, when results can be noted by the dust raised by the strike of bullets on the ground or by the effect of fire upon the enemy. It must be clearly impressed upon the mind of the soldier at this stage that, however skilful individual men may be as marksmen, the greatest effect is produced by their fire only when it is efficiently directed and controlled.
2. (i) The soldier must also be made to understand clearly why effect cannot be obtained from individual fire in battle beyond close range, and why collective fire is necessary for fire effect at all ranges beyond close range. The answer to this question may be stated simply and very broadly as follows: In effect, for various reasons, the individual marksman cannot as a rule see his target clearly or at all with the naked eye beyond close range on service, and he can neither aim at it with accuracy nor be certain of its exact range. Moreover, the effect of inaccurate firing, whether due to excitement, fatigue, or other causes, increases with distance.
(ii) Clearly, therefore, the soldier cannot obtain reasonable assurance of fire effect by individual fire beyond close range. Accordingly, fire-unit commanders equipped with field-glasses discern and indicate targets to him. They give him ranges after they have been ascertained by the use of range-finding instruments, or by observation of fire, when possible, and they direct the fire of a number of individual soldiers in a volume which, whether distributed or concentrated, is sufficient to compensate for individual errors, and so obtain fire effect as described in Secs. 12 and 13, and in Chapter VI.
3. The principal reasons which militate against the assurance of fire effect, by individual fire, beyond close range may be summed up as follows: The effects of fatigue and excitement on the firer; the effects of atmosphere, heat, and light; errors due to imperfections in the rifle and ammunition; uncertainty in estimating longer ranges; the difficulty of discerning and aiming at small, moving, and indistinct or invisible targets; and the steepness of the angle of descent of the bullet, which becomes rapidly accentuated, and so decreases dangerous space as range increases.