Military_Compass.pdf

Instructions for the

US Army Lensatic Compass.

Contains several different

discussions.

Compass, Lensatic,

US Army, Instructions

Instructional Booklet for Military Lensatic, Magnetic Compass

Cammenga & Associates, Inc; 100 Aniline Ave;

Holland, Michigan, 49424; Phone (616) 392-7999

A. INTRODUCTION

The instructions in this booklet are for the Lensatic, Magnetic Compass currently being distributed

by the US Army and Troop Command. This compass is known throughout the world for its precision,

reliability, versatility, ruggedness and much more. It has helped to save lives in time of war and provided

many with recreational and commercial usefulness in times of peace.

The Lensatic compass is used to determine 'azimuths' or 'compass bearings' (horizontal angles). It

is also used to follow a course over the ground, orient or set a map, and determine position of objects in

relation to a map.

B. PARTS OF THE LENSATIC COMPASS Compass, Lensatic, US Army, closeup:

(From another source)

1. LUMINOUS BEZEL INDICATOR: Used to mark a course direction during day or night.

2. N – ARROW OF DIAL: locates magnetic North. The dial is divided into two scales;

a. OUTER -(Black Printing) Graduated in Mils.

6400 Mils to a Circle

Distance Between Black Marks = 20 Mils

Distance Between Black Numerals = 200 Mils

N = 64 (6400) E = 16 (1600), S = 32 (3200), W = 48 (4800)

b. INNER -(Red Printing) Graduated in Degrees

360 Degrees to a Circle

Distance Between Red Marks = 5 Degrees

Distance Between Red Numerals = 20 Degrees

N = 0, E = 90, S = 180, W = 270 Degrees

3. FIVE -INCH RULED SCALE (120 MILLIMETERS): Graduated at a ratio of 1:50,000. Distance on

a 1:50,000 scale map can be measured (with the straight edge) up to 6000 meters 3.7 miles. The

straight edge is useful for measuring distances, orienting a map and aligning bearings.

Note: The map scale index is usually found in the marginal information: However, the

corresponding ground distances of some commonly used map scales are shown below:

SCALE ON MAP DISTANCE OVER GROUND

1:10.560 6" 1 MILE

1:25.000 1" APPROXIMATELY 2000 FT

2.5" 1 MILE

4 CM 1 KM

1:31,680 2" 1 MILE

1:50.000 1.25" 1 MILE

2 CM 1 KM

Numbers such as: (12), are shown in the picture (Compass, Lensatic, US Army - 02.jpg)

4. SIGHT WIRE: Used (along with the sight groove (12) of the lens bracket (10) to set a course over

the ground; or determine an azimuth (bearing, direction) by sighting on prominent terrain features and

reading the compass dial through the lens (11).

5. BEZEL: Contains the luminous bezel indicator (1). Has a serrated edge and rotates with a distinct

clicking action. Each click moves the luminous bezel indicator over a 3 degree arc.

6. CASE COVER: Closes to protect the compass and reduce carrying size. When opened wide (Compass,

Lensatic, US Army - 02.jpg, left side) it can be used as a straight edge or ruler. When perpendicular as

in (Compass, Lensatic, US Army - 03.jpg, a ), the SIGHT WIRE (4) is used to set course.

7. CASE: Contains and protects the dial assembly.

8. THUMB-LOOP: Locks the compass in the closed position (Compass, Lensatic, US Army

- 03.jpg, b, c ) When opened as (Compass, Lensatic, US Army - 03.jpg, a ) It facilitates holding the

compass to a set course to determine an azimuth. (Compass, Lensatic, US Army - 04.jpg)

9. LANYARD: A loop of braided nylon cord to secure the compass around the neck and ease access to it

when carried in a shirt pocket.

10. LENS BRACKET: When pushed all the way down it lifts the dial off the pivot. When the compass is

not being used, it is important to raise the dial in order to prevent damage to the pivot (point on which

the dial balances).

11. LENS: High quality magnifier (about 2.5 inch focal length) to read the compass dial when positioned

about 30 degrees off perpendicular. Handle carefully with clean tissue. Caution: close lens bracket

against bezel glass before closing hinged cover. (Note that this lens is made of plastic, and not glass.)

12. SIGHT GROOVE: Used to set a course over the ground to determine an azimuth when it is used

along with the sight wire (4), the index line (13) and the dial (2).

13. INDEX LINE: Black line etched on the crystal over the dial. Used to read an azimuth.

C. SIGHTING AN AZIMUTH (Taking a Compass Bearing)

1. Open the lensatic compass as shown in (Compass, Lensatic, US Army - 03.jpg, left side).

a. Cover should be perpendicular (90 degrees) to the case.

b. Lens bracket should be tilted about 30 degrees from perpendicular. Be sure the dial floats freely.

2. Sight the Lensatic Compass.

a. Insert thumb through thumb loop (Compass, Lensatic, US Army - 04.jpg)

b. Hold the compass level on the platform formed by the thumb and bent index finger (Compass,

Lensatic, US Army - 04.jpg) .

c. Raise the compass to eye level (Compass, Lensatic, US Army - 04.jpg)

d. Align the center of the sighting groove in the lens bracket with the sight wire and a distant object

- dotted line i (Compass, Lensatic, US Army - 04.jpg)

3. Without moving your head, or the compass, read the azimuth through the lens of the lens bracket,

-dotted line ii (Compass, Lensatic, US Army - 04.jpg) The azimuth, in degrees, is the red number on

the dial lying directly under the black index line of the compass crystal. The azimuth, in mils is the

black number on the outer perimeter of the dial.

D. TO SET A COURSE (FOLLOW A BEARING)

1ST METHOD

a. With the lensatic compass opened wide ((Compass, Lensatic, US Army - 02.jpg -b ) and held level,

turn it horizontally until the azimuth is directly under the black index line. Example: you want to

follow a bearing of 120 degrees. Position the 120 degree mark under the index line.

b. Holding the lensatic compass in this position, rotate the bezel until the luminous indicator is over the

N arrow of the dial. The direction indicated by the open compass is the desired course. As long as the

bezel is not rotated, the course can be checked by turning the open compass so that the luminous bezel

indicator is directly over the n arrow of the dial.

2ND METHOD

a. Turn the fully opened lensatic compass and rotate the bezel to align the luminous bezel indicator, the

black index line and the N arrow of the dial.

b. Subtract the number of degrees, in your desired azimuth, from 360 degrees.

c. Keeping the N arrow under the index line, turn the luminous bezel indicator to this result.

EXAMPLE: You want to follow a course of 120 degrees. Subtract 120 degrees from 360 degrees,

leaving 240 degrees. Keeping the N arrow under the index line, rotate the bezel until the luminous

bezel indicator is over 240 degrees.

d. Turn the compass until the N arrow lies directly under the luminous bezel indicator. The direction

indicated by the open compass cover p31nts the desired course.

3RD METHOD

a. Turn the fully opened compass and rotate the bezel to align the lights in the cover with the luminous

bezel indicator.

b. Rotate the bezel counterclockwise to the azimuth desired.

Each distinct click of the bezel represents 3 degrees.

Example: You want to follow a course of 120 degrees. Divide 120 by 3. The result is 40; therefore

rotate the bezel 40 clicks counter-clockwise.

c. Turn the compass until the N arrow lies directly under the luminous bezel indicator. The direction,

indicated by the lights in the compass cover, points the desired course.

E. PROCEEDING ALONG AN AZIMUTH

1. With your lensatic compass pointing along a desired azimuth. Select an easily identified object that is

in line with the sighting groove of the lens bracket and the sight wire (Compass, Lensatic, US Army -

04.jpg). This 'steering mark' should be distinct from surroundings. It should be visible at all times

along the route and should be identifiable when reached. The greater the distance to a steering mark,

the fewer steering marks you will need to reach your goal.

2. If your steering mark is lost to view, stop, re-sight and select a new steering mark immediately.

3. If a good steering mark is not in line with your desired azimuth, select an alternative steering mark off

to the side.

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