total resistance.com

Determining Direction in the Field

This thread is an overview of how to determine direction using military issued equipment and field-expedient methods. The use of stars, the sun, and geographical reference points with maps, compasses, and other equipment aid in land navigation. [b]FM 21-26[/b] contains additional information on equipment and methods for land navigation.

COMPASS

The lensatic compass consists of a case in which a magnetic dial is mounted on a pivot so that it can rotate freely when the compass is held level (see the Lensatic Compass illustration). Printed on the dial in luminous figures are an arrow and letters E and W. The arrow always points to magnetic north and the letters fall at east (E, 90 degrees), and west (W, 270 degrees). South is at 180 degrees. On the dial are two scales. The outer scale is in mils and the inner scale is in degrees. The front sight is a sighting wire set into a slot in the cover. The rear sight has a slot for sighting on the object and a lens for reading the dial.

GENERAL RULES

Two general rules should always be followed when using the compass.

Rule 1

Keep the compass away from metal objects and high-voltage wires. The north arrow of the compass is controlled by lines of force in the earth's magnetic field. Since these force lines are disturbed locally by small amounts of iron and electric fields, these things will produce error in a compass reading. Even metal rimmed glasses will affect the compass and the effect will be greater as the mass of the object or the strength of the field increases. The extent of the effect can be determined by holding the compass in the palm of the hand and slowly walking away from the object until the dial remains still.

Rule 2

Keep the compass closed when not in use. The compass is a delicate instrument and may easily be damaged. It should always be properly closed and returned to its carrying case when not actually being used.

USE OF THE CENTERHOLD TECHNIQUE

The best method for using the lensatic compass under normal conditions is the centerhold technique (see Centerhold Method illustration below). However, this method is used only when a precise direction is not required. To use this method--

Open the compass so that the cover forms a straight edge with the base. The lens of the compass is moved out of the way.

Place your thumb through the thumb loop, form a steady base with your third and fourth fingers, and extend your index finger along the side of the compass.

Place the thumb of the other hand between the eyepiece and the lens, extend the index finger along the remaining side of the compass, wrap the remaining fingers around the fingers of the other hand, and pull your elbows firmly into your side. This will place the compass between your chin and your belt.

Measure an azimuth, turn your entire body toward the object, and point the compass cover directly at the object. Look down and read the azimuth from beneath the fixed black index line. This method can be used at night.

Keep from going in circles when you are land navigating and stop occasionally to check the azimuth along which you are moving. Also, you can move from object to object along your path by shooting an azimuth to each object and then moving to that object. Repeating this process while you navigate should keep you straight.

USING COMPASS AT NIGHT

Different models of the lensatic compass vary somewhat in the details of their use at night, but the principles are the same. Mounted over the dial, in addition to the stationary glass cover or fixed crystal, is a movable crystal; on this movable crystal is at least one luminous line. To preset the compass for night use, follow these steps.

Light Source Available

Holding the compass in the palm of the hand, rotate it until the desired azimuth falls under the index line. Hold the compass steady so that the desired azimuth remains under the index line, and turn the movable crystal until the luminous line comes over the north arrow.

Light Source not Available

An azimuth may be set on the compass by the click method. As the movable crystal is rotated, a series of clicks is heard. Each of these clicks represents 3 degrees. If the desired azimuth is divided by 3, the number of clicks which can be set off can be determined. To set the azimuth on the compass, rotate the movable crystal until the long luminous line is directly over the index line, and then, holding the compass by the movable crystal, rotate the body of the compass clockwise the desired number of clicks.

Selecting an Object on the Azimuth

With the compass preset as described above, rotate the compass until north arrow falls directly under the luminous line. The body of the compass and the sighting wire are pointing along the required azimuth. Look through the sighting slot and find an object along the sighting wire. (see the Compass-to-Cheek Method illustration). If in a party, it may be expedient to send a man ahead as far as he can be seen and direct him right or left until he is on the desired azimuth. Then move up to his position, reorient the compass with the north arrow under the luminous line, and repeat the process.

Note: The presetting procedure outlined above for using the compass at night may also be used during daylight.

USE OF "OFFSET"

To compensate for our natural tendency to drift from our desired azimuth, especially at night, it may be desirable to offset the compass a few degrees to the left or right of the desired azimuth. The procedure should be used with caution and the amount of "offset" used will be dependent upon the distance to be traveled.

ORIENTATION OF THE MAP USING THE COMPASS

Place the compass on the map so that the cover of the compass is pointing toward the top of the map. Align the sighting wire or the straightedge of the compass over a north-south grid line and rotate the map and compass together until the north arrow of the compass points in the same direction and number of degrees as shown in the current (updated) grid-magnetic angle.

FIELD-EXPEIDIENT METHODS

When a compass is not available, different techniques can be used to determine the four cardinal directions. These techniques do not require special navigational equipment.

SHADOW-TIP METHOD

This simple and accurate method of finding direction by the sun consists of four basic steps. The shadow-tip method is a simple and quick way to determine directions without a compass.

Step One

Place a stick or branch into the ground vertically at a fairly level spot where the sun will cast a distinct shadow. Mark the shadow tip with a stone, twig, or other means. This first shadow mark is always the west direction.

Step Two

Wait 10 to 15 minutes until the shadow tip moves a few inches. Mark the new position of the shadow tip in the same way as the first.

Step Three

Draw a straight line through the two marks made on the shadow tips. This is an east-west line.

Step Four

Stand with the first mark (west) to your left and the second mark to your right. The other directions are simple; north is to the front and south to the back. Remember, the first shadow-tip mark is always in the west direction, everywhere on earth. To find north and south directions, draw a line at a right angle to the east-west line at any point. This is the north-south line. Remember the following rules about shadow-tip directions:

  • The sun rises in the east and sets in the west-- everywhere on earth.
  • The shadow tip moves in the opposite direction.
  • The first shadow-tip mark you make is always west, and the second mark is always east.

    WATCH METHOD

    To determine direction using the watch method, you must use a nondigital watch. Direction is determined using the hour hand and face of the watch. This method is not as accurate as the shadow-tip method. When you are north of the equator (northern hemisphere), point the hour hand at the sun. South will be halfway between your hour hand and 12 o'clock, local standard time. If you are on daylight saving time, south will be midway between the hour hand and 1 o'clock (see the Watch Method illustration). When you are south of the equator (southern hemisphere), you use the watch differently. Point 12 o'clock at the sun. Then, halfway between 12 o'clock and the hour hand is north (see the Watch Method illustration). During daylight saving time, point 1 o'clock at the sun; during daylight saving time, north is midway between 1 o'clock and the hour hand.


    STAR METHOD

    On a clear night, many stars are visible, and if you walk toward the North Star, you will be walking northward. The North Star, however, is not the brightest star in the sky and is sometimes hard to find. To locate the North Star, you should know that--

  • All other stars revolve around the North Star.
  • The North Star is the last star in the handle of the constellation Ursa Minor (Little Dipper), but the complete Little Dipper is often difficult to see.
  • The easiest way to locate the North Star is by using the constellation Ursa Major (Big Dipper). A straight line drawn between the two stars (pointers) at the end of the Big Dipper's bowl will point to the North Star. The distance to the North Star is about five times the distance between the pointers.
  • Directly across from the Big Dipper is the constellation Cassiopeia's chair. It is made up of five stars and resembles a lopsided "M" or "W" depending on its position in the sky. The North Star is straight out from the center star of Cassiopeia's chair. It is almost equidistant between the Big Dipper and the Cassiopeia's chair. (see the Big Dipper illustration). If your are south of the equator you can use the constellation Southern Cross to help you determine the general direction of south. The Southern Cross is a group of four bright stars in the shape of a cross that is tilted to one side. The two stars forming the long axis, or stem, of the cross are called pointers. To determine which direction is south, imagine the long axis extending from its foot five times its length. The point where this imaginary line ends is in the general direction of south (see the Southern Cross illustration). Look straight down from this imaginary point to the horizon and select a landmark.

    "In the beginning of a change, the patriot is a scarce and brave man, hated and scorned. When his cause succeeds however, the timid join him, for then it costs nothing to be a patriot."


    |HOME| |LINKS| |MILITIA SKILLS|