Range determination is a process of finding out the approximate distance from an observer to a target or any distant object. Accurate range determination allows the squad members to set their sights correctly and place effective fire on enemy targets. Methods of determining ranges are estimation by eye and observation of fire.
Estimation by Eye
There are two methods used in estimating range by eye: the mental unit of measure and the appearance of objects. With training and practice, accurate ranges can be determined and a high volume of surprise fire can be delivered on the enemy.
Mental Unit of Measure
- To use the mental unit of measure, the Marine visualizes a 100-meter distance, or any other unit of measure familiar to him. With this unit in mind, he mentally determines how many of these units there are between his position and the target. (See fig. 2-1.) In training, mental estimates should be checked by pacing off the distance. The average man takes about 130 steps per 100 meters.
- Distances beyond 500 meters can most accurately be estimated by selecting a halfway point, estimating the range to this halfway point, then doubling it. (See fig. 2-1.)
Appearance of Objects.
When there are hills, woods, or other obstacles between the observer and target or where most of the ground is hidden from view, it is impractical to apply the mental unit of measure to determine range. In such cases, another method, based on appearance of objects, may be used. Through practice, the Marine learns how objects familiar to him appear at various known ranges. For example, watch a man when he is standing 100 meters away. Fix the appearance of his size and the details of his features and equipment firmly in mind. Watch him in the kneeling position, then in the prone position. By comparing the appearance of a man at 100, 200, 300, and 500 meters, a series of mental pictures is established. When time and conditions permit, accuracy can be improved by averaging a number of estimates by different men to determine the range.
Observation of Fire
Accurate range determination can be made by observing the strike of tracer or ball ammunition. An observer is necessary because it is difficult for a rifleman to follow his own tracer and see its impact. If this method is used, the range may be estimated quickly and accurately, but the possibility of achieving surprise is lost and the firing position may be revealed to the enemy.
This procedure requires that —
- The Marine firing estimates the range by eye, sets his sight for that range, and fires.
- The observer follows the path of the tracer and notes the impact of the round.
- The observer calls out sight corrections in clicks of elevation and windage necessary to hit the target.
- The Marine firing makes sight corrections, and continues to fire and make corrections until a hit on the target is observed. The observer keeps track of the number of clicks of elevation made in getting the round onto the target.
- The final sight setting to hit the target (with consideration to the zero of the rifle) indicates the range to the target. The Marine firing announces the range by voice or signal.