DETERMINING RANGE TO TARGET USING TRIANGULATION and ANGULAR RELATION

We are now at the pinnacle of range finding operations. Many times a sniper team may arrive in an operational where there the target has not yet arrived. Indeed, in many special operations situations, unless the target is material and anchored to the earth, the team will try to arrive long before the target arrives. This allows them to set up the shot on their terms instead of the enemy’s terms. They can set up the shot along the dominant wind line and thereby reduce their crosswind problems. They can also set up the shot so that the sun is behind the sniper team and reduce the target’s security apparatus ability to identify and located the sniper team.

Triangulation is a method that uses a baseline at the sniper’s position and a compass or other angle measuring device (M-2 compasses work better than the military lensetic). This method works when using two operators the best, although one man can do the job. Triangulation measures the angular difference from a line that goes from the gun to the target and a line from a point 90 degrees to that line but between 20 and 50 meters to the right or left of that gun. To do this formula you need a scientific calculator. As mentioned way back in Chapter 3, I recommend the Hewlett Packard HP20S. The appendix to this book contains a program sequence for programming this formula into a HP20S. The key that is important here is the SIN key. This is an extremely accurate method of range determination. Its main use prior to target arrival is setting up a highly detailed range card. Here is the formula:

Range to Target (Line AC) = (AB) X SIN of angle B
SIN of angle C

AC = is the gun to target line.
AB = is the baseline cord length or in the later application, the size of the target.

The baseline cord length has an important impact on the accuracy of the range determination. The larger the baseline when using a compass, the more the accurate the ranging. A GPS makes this process easier. The following cord lengths are based on experience. The operators take a visual range estimation and base their cord length on this estimation.

§ 0-400 Meters = 10-meter cord length
§ 400-600 Meters = 20-meter cord length
§ 600-700 Meters = 30-meter cord length
§ 700-Infinity = 40 or more cord length

A HTI sniper team moves into an area looking for an FFP. They will return to their objective rally point after they obtain some visual Target Reference Points (TRP). Before team lies a major road intersection but there is nothing in that intersection that gives them anything to determine a range on using Angular Deflection or Mil Relation. The team leader directs one of the team members to pull out a roll of “low stretch” cord that is knotted every 5 meters. They are going to execute a triangulation to the intersection that they can build a range card on. At this point they are only gathering minimal data so they can complete their calculations later. The members take a look at the situation and visually estimate a range (and some map use) of about 1400 meters to the intersection.

1. One of the shooters pulls out a compass and a stake that he prepared earlier at the ORP. He drives this stick in the ground at the proposed gun position. He lays his compass on the top of the stake and notes the azimuth to the target. In this case he gets an azimuth of 320 deg. Magnetic (5688 MILS). This establishes line AC.

2. He needs to establish the line AB. By adding 90 degrees to the compass setting he gets a desired azimuth of 50 degrees M. (888 MILS) azimuth. He turns the compass until 50 degrees falls under the indicator line on the compass face. This establishes the AB line angle.

3. Another team member starts at the gun position and runs the cord along this 50 deg. Line. He stays online by directions given him by the compass man. He has determined that due to the terrain and situation a 50-meter baseline cord be used. As he reaches the 50-meter measurement, the compass man gives him a final correction to keep him online as he drives a stake at the Point B of the AB cord.

4. The compass man then moves to Point B where he lays his compass on the stake. He takes an azimuth to the intersection and notes this azimuth. A better method is for one man to line up the compass and a second man takes the reading off the compass face. He gets a direct magnetic reading of 318 deg. Magnetic (5653 MILS). This is a deflection of 2 degrees.

NOTE: A half-degree error in this method results in a difference of 130 meters in the range to the target. An M-2 compass works better because of it’s finer resolving ability using MILS over Degrees.

5. The recon team moves back to the ORP to finish their calculations and finalize their plans. In the ORP, the compass man begins his calculations to get the range to the target. Here are the specifics:

§ AB = 50 Meters
§ Angle B = 88 Degrees / SIN = .99939
§ Angle C = 2 Degrees / SIN = .03490

AC = (50) X SIN B (.99939)divide by SIN C (.03490)

AC = 49.96950 divide by .03490

AC = 1431.790 Meters from Gun to Intersection / Initial Elevation Setting of 71.00 MOA for Mark 211, Mod-0 under Standard Atmospheric Conditions.

6. At the team leaders convenience the shooters can place preliminary elevation data on their gun as the team leader gathers MET and ENV conditions in the target area. Operators can be further dispatched to take wind readings in the area. It is NOT recommended that operators go down into the target area and disturb that area. You never know what security apparatus may move into the area before your shot.

Some tricks can aid the compass man in lying in the AC and AB lines. With the naked compass, it is tough to get an accurate reading. Here are some tricks of the trade.

§ Use a Silva compass mounted to a small wooden or plastic board. The compass is mounted exactly parallel along a centerline in the board. A low power optical sight such as the ACOG from an M-4 system is mounted in front of the board and acts as a precision aiming system for the compass. Have the two about a foot apart so you don’t get magnetic influence from metal in the ACOG scope. This method gets you a very tight on the azimuth to the target. The wire in the lensatic compass sight is thick enough to cover a target at 1500 meters.

§ Binoculars with a compass built into them. Steiner and Leica both offer binoculars with compasses built into them. This also gives you a magnified image of the target as well as the crosshair in the binocular to use as an aiming point at the target area.

§ As stated before, the longer the AB cord, the more accurate the reading will be. It is possible to use a GPS to get an exact fix of your location at the gun. The compass man then takes a reading to the target. While this is going on, another recon element moves to a terrain feature that on the map is 300 meters to the right. When they are in position on the hill, one of them displays a small orange panel that the compass man uses to get them on the required 90-degree angle to the gun-target line. The second team takes a GPS fix and they take a compass reading to the target. By subtracting the coordinates from each other, they can determine exactly how many meters the two teams are apart. This is the AB line. The Angle C will be much larger thereby making the range that much more accurate.

§ AB = 331 Meters after GPS fix
§ Angle B = 77 Degrees M / .97437
§ Angle C = 13 Degrees M / .22495

AC = (331) X .97437
.22495

AC = 1433.725 Meters

As with many of the techniques in this book, these methods are intended to be a jog of the brain as much as locked in cement. Other operators may and will come up with different methods for obtaining an accurate AB cord length. This method requires a good deal of practice in order to prove it’s worth and for the operators to have faith in its ability. Precise use of the compass and other supporting equipment is of utmost importance. When using the GPS use the averaging mode on it to get a super-accurate fix on the location of the gun and the Point B.

To gain an even more accurate range to the target, use multiple methods and repeat your measurements several times. If they vary a little from measurement to measurement, average the measurements out. Of course, another method, but a dangerous one, is to walk out to the target area with the GPS and get a super-accurate averaged fix on the target location. Subtract the two coordinates and you have your range to target.