Making an Improvised Compass – Field Expedient Direction Finding

Making an Improvised Compass – 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 [Approved For Public Release; Distribution is Unlimited] is on making an improvised compass for 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.

MAKING IMPROVISED COMPASSES

Improvised CompassYou can construct improvised compasses using a piece of ferrous metal that can be needle shaped or a flat double-edged razor blade and a piece of nonmetallic string or long hair from which to suspend it. You can magnetize or polarize the metal by slowly stroking it in one direction on a piece of silk or carefully through your hair using deliberate strokes. You can also polarize metal by stroking it repeatedly at one end with a magnet.  Always rub in one direction only.  If you have a battery and some electric wire, you can polarize the metal electrically.  The wire should be insulated.  If not insulated, wrap the metal object in a single, thin strip of paper to prevent contact.  The battery must be a minimum of 2 volts.  Form a coil with the electric wire and touch its ends to the battery’s terminals.  Repeatedly insert one end of the metal object in and out of the coil.  The needle will become an electromagnet.  When suspended from a piece of nonmetallic string, or floated on a small piece of wood in water, it will align itself with a north-south line.

You can construct a more elaborate improvised compass using a sewing needle or thin metallic object, a nonmetallic container (for example, a plastic dip container), its lid with the center cut out and waterproofed, and the silver tip from a pen.  To construct this compass, take an ordinary sewing needle and break in half.  One half will form your direction pointer and the other will act as the pivot point.  Push the portion used as the pivot point through the bottom center of your container; this portion should be flush on the bottom and not interfere with the lid.  Attach the center of the other portion (the pointer) of the needle on the pen’s silver tip using glue, tree sap, or melted plastic.  Magnetize one end of the pointer and rest it on the pivot point.

OTHER MEANS OF DETERMINING DIRECTION

The old saying about using moss on a tree to indicate north is not accurate because moss grows completely around some trees. Actually, growth is more lush on the side of the tree facing the south in the Northern Hemisphere and vice versa in the Southern Hemisphere. If there are several felled trees around for comparison, look at the stumps.  Growth is more vigorous on the side toward the equator and the tree growth rings will be more widely spaced.  On the other hand, the tree growth rings will be closer together on the side toward the poles.

Wind direction may be helpful in some instances where there are prevailing directions and you know what they are.

Recognizing the differences between vegetation and moisture patterns on north- and south-facing slopes can aid in determining direction.  In the northern hemisphere, north-facing slopes receive less sun than south-facing slopes and are therefore cooler and damper.  In the summer, north-facing slopes retain patches of snow. In the winter, the trees and open areas on south-facing slopes are the first to lose their snow, and ground snowpack is shallower.

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