1. Importance of Ranging.—(i) Accurate ranging when firing is of vital importance, especially at distances beyond close range. Mistakes in judging distance or range-finding, and errors in sighting, cause a greater loss of fire effect than personal errors in shooting except at close range. But even within close range mistakes of more than 100 yards are not infrequently made in judging distance. The more accurate the firing, the less will be the result if the sighting is incorrect from any cause.
(ii) The measurement of ranges will commence the moment a firing-point has been chosen. Range-taking increases in importance rapidly with every 100 yards beyond 600 yards up to 2,000 yards, at which distance troops not in a close formation are only visible when in motion, or with a very favourable background or light.
2. Methods of Ranging.—(i) The principal means of ranging are—(a) Judging distance by eye; (b) observation of fire; (c) use of instruments such as the mekometer and the one-man range-finder. There are several auxiliary methods of ranging such as back-reckoning, use of maps, information obtained from aircraft, artillery or machine-guns, sound and flash, cross-bearings, etc., which may be used occasionally or in exceptional cases.
(ii) Observation of fire, when possible, is an effective means of ranging. If uncertainty exists as to elevation, it is better to underestimate than to overestimate the range. If it is necessary to fire at ranges beyond 1,000 yards, and observation is not possible, or the situation demands that some effect should be produced, quickly combined sights may be employed. In all cases every available means should be employed to find correct ranges. No available means of ascertaining ranges should ever be neglected, if time and opportunity allow them to be used.
3. Reconnaissance as an Aid to Ranging.—As already stated, range-finding will as a rule be in progress before fire is opened, and the rapid reconnaissance of any ground on which a fire-fight is likely to take place should provide information of the greatest value to company officers responsible for the direction of fire. In preparing a defensive position, there is usually ample time for ascertaining ranges, and for using range-marks (Sec. 40, para. 5) and preparing range-cards (Sec. 40, para. 1).
4. Training of Officers and N.C.O.’s.—As fire is controlled at longer ranges, practice in judging distance is more necessary for officers and non-commissioned officers than for the private soldier. Soldiers who show aptitude in judging short distances by eye should, however, be given training with their leaders at judging longer distances. These men may also be selected for training in the use of range-finding instruments and in the duties of observers (Sec. 42, para. 9).
5. Reduction of Errors by Training.—Officers and non-commissioned officers, by constant practice, will reduce their mean error in judging distance from about 20 per cent. of the correct distance to about 10 per cent., but much depends on the local conditions to which the observer is accustomed. With thorough training the mean error of private soldiers in judging distances within 800 yards should not exceed 100 yards. Special attention should be paid to men whose mean errors exceed this distance, with a view to discovering the cause and reducing the error.
6. Effect of Strange Conditions.—Serious errors must be expected in judging under strange conditions of ground and atmosphere. Exercises in judging distance must therefore be carried out before, as well as during, military operations in unfamiliar country.
Section 37.—Judging Distances by Eye.
1. Methods of Judging Distance by Eye.—Distances may be judged by eye in the following ways: (a) By measuring the intervening ground with the eye in terms of some familiar unit, such as 100 yards; (b) by the apparent size of the object, if its size is known, or, in other words, by visual angles; (c) by the visibility of the object as affected by light, atmospheric effect, background, etc.