Ok, now that you have possession of your G.I. Lensatic Compass, here is one thing you can do with it.

INTERSECTION

Suppose you want to find the location of an unknown point by successively occupying at least two but preferably three (triangulation) known positions by sighting on the unknown point.  This is called intersection.

It is used to locate features that are not defined on the map or which are not readily identifiable.  Here is what you do with the Map and Compass method:

(1) Orient the map to north using the compass.

(2) Locate and mark your position on the map.

(3) Measure the magnetic azimuth to the unknown position; convert to grid azimuth.

(4) Draw a line on the map from your position on this grid azimuth.

(5) Move to a second known position from which the unknown point is visible.  Locate this position on the map and again orient the map using the compass.

(6) Repeat (3) and (4) above.

(7) As a check on accuracy, move to a third position and repeat (1) through (4) above.

(8) Where the lines cross is the location of the unknown position.  Using three lines a triangle is sometimes formed instead of an intersection.  This is called the triangle of error.  If the triangle is large, recheck you work to find the error.  WARNING: Do not assume that the position is at the center of the triangle.

In the diagram above, positions A, B, and C  are the known positions in which you are observing the the Location of Feature or Unknown position.  By taking a bearing with the G.I. Lensatic Compass at each position, and transfering those measurements to your map (correcting for magnetic declination) you will have accurately plotted the unknown object’s location on your map.

This know-how is useful when coupled with a YAGI handheld directional antenna for finding the source of a transmitting radio. 

By using a directional YAGI antenna for the band (frequency) that you are needing to search for and a signal strength meter, you can derive an azimuth reading from your compass by shooting a line in the direction of strongest signal.  These antennas are relatively inexpensive, but delicate.  They are used for locating beacons on animals and tracking hidden transmitters.  They could also be used by forward Patriot intelligence gatherers to locate the position of “radio traffic” within your perimeter of defense or operational area.

This lesson was adapted from Army Field Manual FM 21-26: Map Reading.  You can get this manual and a shitload more from this site all bundled together into one secure download for only $6.99.  Click the banner below for more information:

Bookmark It

Filed under: Tutorials by Patriot75