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Chapter 4

Range Determination

Range determination significantly affects target engagement accuracy. Errors in range determination will cause more first-round misses than errors in deflection. Range errors that cause the first round to go over the target are particularly serious because the round travels over the target, and the strike of the round is obscured by the target, making subsequent adjustments extremely difficult.

The vehicle commander is responsible for navigation and command and control. He uses his knowledge of the terrain, the tactical situation, and the friendly control measures on his map and on the ground, and his experience to determine range. He can determine range using the naked eye, binoculars with mil-relation formula (the assisted method), a map, or one of the other methods of range determination; these methods can be used separately or combined.

Primary Range Determination Methods

NAKED EYE METHOD

The vehicle commander, with practice, can estimate distances out to about 1,000 meters. This is particularly useful in close-in, immediate engagement situations where no time is available for using sights, binoculars, or maps. A technique for accomplishing this is the football field method. The vehicle commander counts 100-meter increments, estimating the number of football fields that could fit between him and the target.

Note. The driver and gunner can also use this method to determine ranges to close-in targets.

The vehicle commander must be aware that light, weather, and terrain conditions can make a target look nearer or farther than it is. Conditions that make a target appear to be nearer are--

  • A bright, clear day.
  • Sun in front of the target.
  • High elevations.
  • Large targets.
  • Bright colors (white, red, and yellow).
  • Contrast.
  • Looking across ravines, hollows, rivers, and depressions.

Conditions that make a target appear to be farther are--

  • Fog, rain, haze, smoke, dusk, and dawn.
  • Sun behind the target.
  • Low elevations.
  • Small targets.
  • Dark target colors (brown, black, and green).
  • Camouflaged targets (paint, netting).

ASSISTED METHOD (BINOCULARS WITH MIL-RELATION FORMULA)

The binoculars and mil relation are used in the assisted method of range determination. To use this method, the width or height of the target must be known. Using the known threat vehicle width or height with the binocular mil scale, substitute the mil relation and compute the range. When measuring the frontal width, measure only the vehicle front slope (from left front corner to right front corner). When measuring flank width, measure the entire vehicle. Accuracy of this method depends on the target dimensions and the vehicle commander's ability to make precise measurements with the binoculars (see Figure 4-1).

Note. The distance between tick marks on the horizontal scale is 10 mils.

Figure 4-1. Target Measurement Using Binocular Reticle.

The mil is a unit of angular measurement equal to 1/6400 of a circle. There are 18 mils in one degree. One mil equals the width (or height) of 1 meter at a range of 1,000 meters. This relation is constant as the angle increases from one mil to two mils, and the range increases from 1,000 meters to 2,000 meters. Because the mil relation is constant, other units of measurement (such as yards, feet, or inches) can be substituted to express width or range; however, both width and range must be expressed in the same unit of measurement. For example, if the sides of a one-mil angle are extended to 1,000 yards, the width between the ends of the sides is 1 yard.

Since the relationship of the target width in mils (m) to the target width (W) in meters is constant at varying distances, accurate range determination is possible. The mil relation holds true whether the W factor is length, width, or height; therefore, the range can be determined if the target dimensions are known.

To determine the range (R), the m and W factors must be known.

The m comes from reading the target width (height or length) on the mil scale in the binoculars. The W comes from Table 4-1, Mil Relation for Various Targets, or other vehicle identification aids (GTA 17-2-13 or FM 23-1), and is expressed in meters.

MIL RELATION FOR VARIOUS TARGETS
This table is a quick reference for determining the range to threat vehicles. Threat vehicles have been grouped, and the sizes of the vehicles have been averaged.
Group 1 (BMP, Tank, BTR, ZSU, OT MT-LB, and TAB)
Target width (mils) 5 4.5 4 3.5 3 2.5 2 1.5 1
Flank 5.5m 1,400 1,600 1,800 2,000 2,300 2,800 3,400 4,600 6,900
Front 3.0m 600 700 800 900 1,000 1,200 1,600 2,000 3,000
Group 2 (BMD and BRDM)
Target width (mils) 5 4.5 4 3.5 3 2.5 2 1.5 1
Flank 5.5m 1,200 1,300 1,400 1,600 1,800 2,200 2,800 3,800 5,500
Front 2.35m 400 500 600 700 800 1,000 1,200 1,600 2,400
Group 3 (HIND-D Helicopters)
Target width (mils) 22.5 20 17.5 15 12.5 10 7.5 5 2.5
Flank 17.255m 800 900 1,000 1,200 1,400 1,800 2,400 3,600 7,000
Target width (mils) 5 4.5 4 3.5 3 2.5 2 1.5 1
Front 6.9m 1,400 1,600 1,800 2,000 2,400 2,800 3,600 4,600 6,900

Table 4-1. Mil Relation for Various Targets.

The known target width (W) is then divided by the mil (m) width; this equals the range (R) factor. Multiply R by 1,000 to determine the target range. For example, a BMP is 6.75 meters long (W). Using binoculars, the vehicle commander determines that a BMP measures 5 mils in length (W ÷ m = R). Substitute the two known values for W and m and round to the nearest tenth (6.75 ÷ 5 = 1.35 = 1.4). Since R is expressed in thousands of meters, multiply by 1,000 (1.4 X 1,000 = 1,400 meters, the range to the BMP).

Table 4-1 shows the results of the computation for threat vehicles at various ranges. Determine the width of the target in mils. The range to the target is listed in the column below the mil measurement. Be sure to use the correct range, depending on whether the vehicle is viewed from the front or flank.

MAP METHOD

The map method can be used to determine range; however, it is the slowest method and should only be used during defensive operations, when time is available. To use the map method, the vehicle commander measures the distance from his known location to the target's location on the map to determine range within 200 meters. This method requires the vehicle commander to constantly track his location and rapidly determine the location of the target vehicle using six-digit grid coordinates. The map method should be used during planning by predetermining the location of engagement areas and suspected enemy positions, providing the vehicle commander reference points to determine range. This method is most commonly used in defense for determining range for sector sketches and platoon fire plans.

Other Methods

TARGET REFERENCE POINTS

TRPs are used as fire control measures for both direct and indirect fire, and are entered in the sector sketch to help the vehicle commander determine range and control his fires.

RANGE CARDS

The primary use of the range card is to assist the crew in engaging targets during limited visibility. The vehicle commander may also use the range card to determine range, since ranging data is recorded on the range card.

LASER RANGE FINDER

Laser range finders, such as the AN/GVS-5 and PVS-6, are the quickest and most accurate devices available to determine range.



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