Field Expedient Direction Finding

Andrew’s Note:  Today we present another lesson from our Military Pedagogy series.

This discussion, from FM 21-76, the U.S. Army Survival Manual is on using the Shadow Tip Method of Field Expedient Direction Finding.

In a survival situation, you will be extremely fortunate if you happen to have a map and compass.

If you do have these two pieces of equipment, you will most likely be able to move toward help.  If you are not proficient in using a map and compass, you must take the steps to gain this skill.

There are several methods by which you can determine direction by using the sun and the stars.

These methods, however, will give you only a general direction.  You can come up with a more nearly true direction if you know the terrain of the territory or country.

You must learn all you can about the terrain of the country or territory to which you or your unit may be sent, especially any prominent features or landmarks.

This knowledge of the terrain together with using the methods explained below will let you come up with fairly true directions to help you navigate.

USING THE SUN AND SHADOWS

Figure 18-1 Shadow Tip Method
The earth’s relationship to the sun can help you to determine direction on earth.  The sun always rises in the east and sets in the west, but not exactly due east or due west. There is also some seasonal variation.  In the northern hemisphere, the sun will be due south when at its highest point in the sky, or when an object casts no appreciable shadow.  In the southern hemisphere, this same noonday sun will mark due north.  In the northern hemisphere, shadows will move clockwise. Shadows will move counterclockwise in the southern hemisphere.  With practice, you can use shadows to determine both direction and time of day.  The shadow methods used for direction finding are the shadow-tip and watch methods.

Shadow-Tip Methods

In the first shadow-tip method, find a straight stick 1 meter long, and a level spot free of brush on which the stick will cast a definite shadow.  This method is simple and accurate and consists of four steps:

    • Step 1.  Place the stick or branch into the ground at a level spot where it will cast a distinctive shadow.  Mark the shadow’s tip with a stone, twig, or other means.  This first shadow mark is always west–everywhere on earth.
    • Step 2.  Wait for 10 to 15 minutes until the shadow tip moves a few centimeters.  Mark the shadow tip’s new position in the same way as the first.
    • Step 3.  Draw a straight line through the two marks to obtain an approximate east-west line.
    • Step 4.  Stand with the first mark (west) to your left and the second mark to your right–you are now facing north. This fact is true everywhere on earth.

An alternate method is more accurate but requires more time. Set up your shadow stick and mark the first shadow in the morning.

Use a piece of string to draw a clean arc through this mark and around the stick.  At midday, the shadow will shrink and disappear.

In the afternoon, it will lengthen again and at the point where it touches the arc, make a second mark.

Draw a line through the two marks to get an accurate east-west line (see Figure 18-1).

This is is a syndicated post. Read the original at prepography.com

   

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