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Compasses are the primary navigation tools to use when moving in an outdoor
world where there is no other way to find directions.
Soldiers should be thoroughly familiar with the compass and its uses. Part One
of this manual discussed the techniques of map reading. To complement these
techniques, a mastery of field movement techniques is essential. Below we
describe the lensatic compass and its uses, and some of the field expedient
methods used to find directions when compasses are not available.
The
lensatic compass is the most common and
simplest instrument for measuring direction. The artillery M2 compass
is a special-purpose
instrument designed for accuracy. The wrist/pocket compass is a small
magnetic compass that can be attached to a wristwatch band. It contains a
north-seeking arrow and a dial in degrees. A protractor can be used to
determine azimuths when a compass is not available. However, it should be
noted that when using the protractor on a map, only grid azimuths are
obtained.
The lensatic
compass consists of three major parts: the cover, the base, and the
lens.
a . Cover. The
compass cover protects the floating dial. It contains the sighting wire (front
sight)
and two luminous sighting slots or dots used for night navigation.
b . Base. The
body of the compass contains the following movable parts:
(1) The floating dial is mounted on a pivot so it can
rotate freely when the compass is held level.
Printed on the dial in luminous figures are an arrow and the letters E and
W. The arrow always points to magnetic north
and the letters fall at east (E) 90° and west (W) 270° on the dial. There
are two scales; the outer scale denotes mils and the inner scale (normally
in red) denotes degrees.
(2) Encasing the floating dial is a glass containing
a fixed black index line.
(3) The bezel ring is a ratchet device that clicks
when turned. It contains 120 clicks when rotated fully; each click is equal to
3°.
A short luminous line that is used in conjunction with the north-seeking
arrow during navigation is contained in the glass face of the bezel ring.
(4) The thumb loop is attached to the base of the
compass.
c . Lens. The
lens is used to read the dial, and it contains the rear-sight slot used in
conjunction with the front for
sighting on objects. The rear sight also serves as a lock and clamps the
dial when closed for its protection. The rear sight must be opened more than
45°
to allow the dial to float freely.
Compasses are delicate instruments and should be cared for
accordingly.
a . Inspection.
A detailed inspection is required when first obtaining and using a compass.
One of the most important parts to check is the
floating dial, which contains the magnetic needle. The user must also make
sure the sighting wire is straight, the glass and crystal parts are not
broken, the numbers on the dial are readable, and most important, that the
dial does not stick.
b . Effects of
Metal and Electricity. Metal objects and electrical sources can affect the
performance of a compass. However, nonmagnetic metals
and alloys do not affect compass readings. The following separation
distances are suggested to ensure proper functioning of a compass:
| High-tension power lines
..................................................... |
55 meters |
| Field gun, truck, or tank
....................................................... |
18 meters |
| Telegraph or telephone wires and barbed
wire .................. |
10 meters |
| Machine
gun .......................................................................
. |
2 meters |
| Steel helmet or
rifle ............................................................. |
1/2 meter |
c . Accuracy.
A compass in good working condition is very accurate.
However, a compass has to be checked periodically on a known line of
direction, such as a surveyed azimuth using a declination station. Compasses
with more than 3° + variation should not be used.
d .
Protection. If traveling with the compass unfolded, make sure the rear
sight is fully folded down onto the bezel ring. This will lock the
floating dial and prevent vibration, as well as protect the crystal and rear
sight from damage.
USING A COMPASS
Magnetic azimuths are determined with the use of magnetic
instruments, such as lensatic and M2 compasses. The techniques employed when
using the lensatic
compass are as follows:
a . Using the
Centrefold Technique. First, open the compass to its fullest so that the
cover forms a straightedge with the base. Move the lens
(rear sight) to the rearmost position, allowing the dial to float freely.
Next, 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 lens (rear sight) and
the bezel
ring; extend the index finger along the remaining side of the compass, and
the remaining fingers around the fingers of the other hand. Pull your elbows
firmly into your sides; this will place the compass between your chin and
your belt. To measure an azimuth, simply turn your entire body toward the
object,
pointing the compass cover directly at the object. Once you are pointing at
the object, look down and read the azimuth from beneath the fixed black index
line. This preferred method offers the following advantages over the
sighting technique:
(1) It is faster and easier to use.
(2) It can be used under all
conditions of visibility.
(3) It can be used when navigating over any
type of terrain.
(4) It can be used without putting down the rifle;
however, the rifle must be slung well back over either shoulder.
(5) It
can be used without removing eyeglasses.
b . Using the Compass-to-Cheek
Technique. Fold the cover of the
compass containing the sighting wire to a vertical position; then fold the
rear sight slightly forward. Look through the rear-sight slot and align the
front-sight hairline with the desired object in the distance. Then glance
down at the dial through the eye lens to read the azimuth.
NOTE: The compass-to-cheek technique is used almost exclusively for
sighting, and it is the best technique for this purpose.
c . Presetting a Compass and
Following an Azimuth. Although
different models of the lensatic compass vary somewhat in the details of
their use, the principles are the same.
(1) During daylight hours or with a light source:
(a) Hold the compass level in the palm of the hand.
(b)
Rotate it until the desired azimuth falls under the fixed black index line
(for example, 320°), maintaining the azimuth as prescribed.
(c) Turn the bezel ring until the luminous line is
aligned with the north-seeking arrow. Once the alignment is obtained, the
compass is preset.
(d) To follow an azimuth, assume the centerhold
technique and turn your body until the north-seeking arrow is aligned with the
luminous line.
Then proceed forward in the direction of the front cover's sighting
wire, which is aligned with the fixed black index line that contains the
desired
azimuth.
(2) During limited visibility, an azimuth may be set
on the compass by
the click method. Remember that the bezel ring contains 3° intervals
(clicks).
(a) Rotate the bezel ring until the luminous line
is over the fixed black index line.
(b) Find the desired azimuth and divide it by
three. The result is the number of clicks that you have to rotate the bezel
ring.
(c) Count the desired number of clicks. If the
desired azimuth is smaller than 180°, the number of clicks on the bezel ring
should be
counted in a counter clockwise direction. For example, the desired
azimuth is 51°. Desired azimuth is 51°¸ 3 = 17 clicks
counter clockwise. If the
desired azimuth is larger than 180°, subtract the number of degrees from
360° and divide by 3 to obtain the number of clicks. Count them in a
clockwise direction. For example, the desired azimuth is 330°; 360°-330°
= 30 ¸ 3 = 10 clicks clockwise.
(d) With the compass preset as described above,
assume a
centrefold technique and rotate your body until the north-seeking arrow
is aligned
with the luminous line on the bezel. Then proceed forward in the
direction of the front cover's luminous dots, which are aligned with the fixed
black
index line containing the azimuth.
(e) When the compass is to be used in darkness, an
initial azimuth should be set while light is still available, if possible.
With the
initial azimuth as a base, any other azimuth that is a multiple of three
can be established through the use of the clicking feature of the bezel
ring.
NOTE: Sometimes the desired azimuth is not
exactly divisible by three, causing an option of rounding up or rounding down.
If
the azimuth is rounded up, this causes an increase in the value of the
azimuth, and the object is to be found on the left. If the azimuth is
rounded down, this causes a decrease in the value of the azimuth, and the
object is to be found on the right.
d.
Bypassing an Obstacle. To bypass enemy positions or obstacles and
still stay oriented, detour around the obstacle by moving at right angles
for specified distances.
(1) For example, while moving on an azimuth of 90°
change your azimuth
to 180° and travel for 100 meters. Change your azimuth to 90°and travel
for 150 meters. Change your azimuth to 360°and travel for 100 meters. Then,
change your azimuth to 90°and you are back on your original azimuth
line.
(2) Bypassing an unexpected obstacle at night is a
fairly simple matter.
To make a 90° turn to the right, hold the compass in the centrefold
technique; turn until the
centre of the luminous letter E is under the
luminous line (do not move the bezel ring). To make a 90° turn to
the left, turn until the
centre of the luminous letter W is under the luminous
line. This does not require changing the compass setting (bezel ring), and
it ensures accurate 90° turns.
e . Offset. A
deliberate offset is a planned magnetic deviation to
the right or left of an azimuth to an objective. Use it when the objective
is located along or in the vicinity of a linear feature such as a road or
stream.
Because of errors in the compass or in map reading, the linear feature may
be reached without knowing whether the objective lies to the right or left. A
deliberate offset by a known number of degrees in a known direction
compensates for possible errors and ensures that upon reaching the linear
feature, the user knows whether to go right or left to reach the objective.
Ten degrees is an adequate offset for most tactical uses. Each degree offset
moves the course about 18 meters to the right or left for each 1,000 meters
travelled. In the example below, the number of degrees offset is 10. If the
distance
travelled
to 'x' in 1,000 meters, then 'x' is located about 180 meters to the right of
the objective.
FIELD-EXPEDIENT METHODS
When a compass is not available, different techniques should be used to
determine the four cardinal directions.
a . Shadow-Tip Method.
(1) This simple and accurate method of finding direction by the sun
consists of four basic steps.
Step 1. Place a stick or branch into the ground at
a level spot where a distinctive shadow will be cast. Mark the shadow tip with
a
stone, twig, or other means. This first shadow mark is always the west
direction.
Step 2. 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 3. Draw a straight line through the
two marks to obtain an approximate east-west line.
Step 4. Standing with the first mark
(west) to your left, the other directions are simple; north is to the front,
east is to the
right, and south is behind you.
(2) A line drawn perpendicular to the east-west
line at any point is the approximate north-south line. If you are uncertain
which
direction is east and which is west, observe this simple rule--the
first shadow-tip mark is always in the west direction, everywhere on earth.
(3) The shadow-tip method can also be used as a
shadow clock to
find the approximate time of day.
(a) To find the time of day, move the stick to
the intersection
of the east-west line and the north-south line, and set it
vertically
in the ground. The west part of the east-west line indicates 0600
hours, and the east part is 1800 hours, anywhere on earth, because
the
basic rule always applies.
(b) The north-south line now becomes the noon
line. The shadow of
the stick is an hour hand in the shadow clock, and with it you can
estimate the time using the noon line and the 6 o'clock line as your
guides. Depending on your location and the season, the shadow may
move
either clockwise or counterclockwise, but this does not alter your
manner of reading the shadow clock.
(c) The shadow clock is not a timepiece in the
ordinary sense. It
makes every day 12 unequal hours long, and always reads 0600 hours
at
sunrise and 1800 hours at sunset. The shadow clock time is closest
to
conventional clock time at midday, but the spacing of the other
hours
compared to conventional time varies somewhat with the locality and
the date. However, it does provide a satisfactory means of telling
time in the absence of properly set watches.
(d) The shadow-tip system is not intended for
use in polar
regions, which the Department of Defense defines as being above 60°
latitude in either hemisphere. Distressed persons in these areas are
advised to stay in one place so that search/rescue teams may easily
find them. The presence and location of all aircraft and ground
parties in polar regions are reported to and checked regularly by
governmental or other agencies, and any need for help becomes
quickly
known.
b . Watch Method.
(1) A watch can be used to determine the
approximate true north and
true south. In the north temperate zone only, the hour hand is pointed
toward the sun. A south line can be found midway between the hour hand
and 1200 hours, standard time. If on daylight saving time, the north-
south line is found between the hour hand and 1300 hours. If there
is any doubt as to which end of the line is north, remember that the
sun is in the east before noon and in the west after noon.
(2) The watch may also be used to determine
direction in the south temperate zone; however, the method is different. The
1200-hour dial is
pointed toward the sun, and halfway between 1200 hours and the hour
hand will be a north line. If on daylight saving time, the north line lies
midway between the hour hand and 1300 hours.
(3) The watch method can be in error, especially
in the lower latitudes, and may cause circling. To avoid this, make a
shadow
clock and set your watch to the time indicated. After traveling for an
hour, take another shadow-clock reading. Reset your watch if necessary.
c . Star Method.
(1) Less than 60 of approximately 5,000 stars
visible to the eye are used by navigators. The stars seen as we look up at the
sky at night
are not evenly scattered across the whole sky. Instead they are in
groups called constellations.
(2) The constellations that we see depends partly
on where we are located on the earth, the time of the year, and the time of
the night.
The night changes with the seasons because of the journey of the earth
around the sun, and it also changes from hour to hour because the
turning of the earth makes some constellations seem to travel in a
circle. But there is one star that is in almost exactly the same place
in the sky all night long every night. It is the North Star, also
known as the Polar Star or Polaris.
(3) The North Star is less than 1° off true north
and does not move from its place because the axis of the earth is pointed
toward it. The
North Star is in the group of stars called the Little Dipper. It is
the last star in the handle of the dipper. There are two stars in the Big
Dipper, which are a big help when trying to find the North Star. They
are called the Pointers, and an imaginary line drawn through them five
times their distance points to the North Star. There are many stars
brighter than the North Star, but none is more important because of its
location. However, the North Star can only be seen in the northern
hemisphere so it cannot serve as a guide south of the equator. The
farther one goes north, the higher the North Star is in the sky, and
above latitude 70°, it is too high in the sky to be useful.
(4) Depending on the star selected for
navigation, azimuth checks are necessary. A star near the north horizon serves
for about half an
hour. When moving south, azimuth checks should be made every 15
minutes. When
travelling east or west, the difficulty of staying on azimuth is
caused more by the likelihood of the star climbing too high in the sky
or losing itself behind the western horizon than it is by the star
changing direction angle. When this happens, it is necessary to change
to another guide star. The Southern Cross is the main constellation used
as a guide south of the equator, and the above general directions for
using north and south stars are reversed. When navigating using the
stars as guides, the user must know the different constellation shapes
and their locations throughout the world.
Constellations, northern hemisphere.
Constellations, southern hemisphere.
GLOBAL POSITIONING SYSTEM
The GPS is a space-based, global, all-weather, continuously
available, radio positioning navigation system. It is highly accurate in
determining position location derived from signal triangulation from a
satellite constellation system. It is capable of determining latitude,
longitude, and
altitude of the individual user. It is being fielded in hand-held, manpack,
vehicular, aircraft, and watercraft configurations. The GPS receives and
processes data from satellites on either a simultaneous or sequential basis.
It measures the velocity and range with respect to each satellite, processes
the
data in terms of an earth-centered, earth-fixed coordinate system, and
displays the information to the user in geographic or military grid
coordinates.
a . The GPS can
provide precise steering information, as well as position location. The
receiver can accept many checkpoints entered in any coordinate system by the
user and convert them to the desired coordinate system. The user then calls up
the desired checkpoint and the receiver will display direction and distance to
the checkpoint. The GPS does not have inherent drift, an improvement over the
Inertial Navigation System, and the receiver will automatically update its
position. The receiver can also compute time to the next checkpoint.
b . Specific
uses for the GPS are position location; navigation; weapon location; target
and sensor location; coordination of firepower; scout and screening
operations; combat resupply; location of obstacles, barriers, and gaps; and
communication support. The GPS also has the potential to allow units to train
their soldiers and provide the following:
- Performance feedback
- Knowledge of routes taken by the soldier
- Knowledge of errors committed by the soldier
- Comparison of planned versus executed routes
- Safety and control of lost and injured soldiers
GPS DEFINITION
The ability to accurately determine position location
has always been a major problem for soldiers. However, the global positioning
system
has solved that problem. Soldiers will now be able to determine their position
accurately to within 10 meters.
The GPS is a satellite-based, radio navigational system. It
consists of a constellation with 24 active satellites that interfaces with a
ground-, air-, or sea-based receiver. Each satellite transmits data that
enables the GPS receiver to provide precise position and time to the user. The
GPS
receivers come in several configurations, hand-held, vehicular-mounted,
aircraft-mounted, and watercraft-mounted.
GPS OPERATION
The GPS is based on satellite ranging. It figures the
users’ position on earth by measuring the distance from a group of satellites
in space
to the users’ location. For accurate three-dimensional data, the receiver must
track four or more satellites. Most GPS receivers provide the user with the
number of satellites that it is tracking, and whether or not the signals are
good. Some receivers can be manually switched to track only three satellites
if
the user knows his altitude. This method provides the user with accurate data
much faster than that provided by tracking four or more satellites. Each type
receiver has a number of mode keys that have a variety of functions. To better
understand how the GPS receiver operates, refer to the operators' manual.
GPS CAPABILITIES
The GPS provides worldwide, 24-hour, all-weather, day or
night coverage when the satellite constellation is complete. The GPS can
locate
the position of the user accurately to within 21 meters—95 percent of the
time. However, the GPS has been known to accurately locate the position of the
user
within 8 to 10 meters. It can determine the distance and direction from the
user to a programmed location or the distance between two programmed locations
called
way points. It provides exact date and time for the time zone in which the
user is located. The data supplied by the GPS is helpful in performing several
techniques, procedures, and missions that require soldiers to know their exact
location. Some examples are:
- Sighting
- Surveying
- Sensor or minefield emplacement
- Forward observing
- Close air support
- Route planning and execution
- Amphibious operations
- Artillery and mortar emplacement
- Fire support planning
GPS LIMITATIONS
A constellation of 24 satellites broadcasts precise signals
for use by navigational sets. The satellites are arranged in six rings that
orbit the earth twice each day. The GPS navigational signals are similar to
light rays, so anything that blocks the light will reduce or block the
effectiveness of the signals. The more unobstructed the view of the sky, the
better the system performs.
GPS COMPATABILITY
All GPS receivers have primarily the same function, but the
input and control keys vary between the different receivers. The GPS can
reference and format position coordinates in any of the following systems:
-
Degrees, Minutes, Seconds (DMS):
Latitude/longitude-based system with position expressed in degrees, minutes,
and seconds.
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Degrees, Minutes (DM): Latitude/longitude-based
system with position expressed in degrees and minutes.
-
Universal Traverse Mercator (UTM): Grid zone
system with the northing and easting position expressed in meters.
-
Military Grid Reference System (MGRS): Grid
zone/grid square system with coordinates of position expressed in meters.
The following is a list of land navigation subjects from
other sections of this manual in which GPS can be used to assist soldiers in
navigating and map reading:
a. Grid Coordinates. GPS makes determining a 4-, 6-
, 8-, and 10-digit grid coordinate of a location easy. On most GPS
receivers, the position mode will give the user a 10-digit grid coordinate to
their present location.
b. Distance and Direction. The mode for
determining distance and direction depends on the GPS receiver being used. One
thing the different types of receivers have in common is that to determine
direction and distance, the user must enter at least one way point (WPT). When
the receiver measures direction and distance from the present location or
from way point to way point, the distance is measured in straight line only.
Distance can be measured in miles, yards, feet, kilometers, meters, or
nautical knots or feet. For determining direction, the user can select
degrees, mils, or rads. Depending on the receiver, the user can select true
north, magnetic north, or grid north.
c. Navigational Equipment and Methods. Unlike
the compass, the GPS receiver when set on navigation mode (NAV) will guide the
user to a selected way point by actually telling the user how far left or
right the user has drifted from the desired azimuth. With this option, the
user can take the most expeditious route possible, moving around an obstacle
or area without replotting and reorienting.
d. Mounted Land Navigation. While in the NAV
mode, the user can navigate to a way point using steering and distance, and
the
receiver will tell the user how far he has yet to travel, and at the current
speed, how long it will take to get to the way point.
e. Navigation in Different Types of Terrain. The
GPS is capable of being used in any terrain, especially more open terrain like
the desert.
f. Unit Sustainment. The GPS can be used to read
coordinates to quickly and accurately establish and verify land navigation
courses.
Hiking Boots are all based on something called a 'last,'
which is the solid plastic mould around which the boot is built. The last is
an approximation of what the manufacturer assumes to be the average foot. An
upper is formed around the last, and the segments are stitched together. These
stitched areas are called seams. More seams allow a boot to fit more
conclusively, they are also
the weakest link and the first thing to blow out on the trail.
The thickness of the material used to make the upper is called the gauge. The
leather will be either top-grain (formerly the outside skin of a cow)
or 'other.' Virtually all mid-range to high quality boots use top-grain. The
leather is either smooth-out or rough-out. Smooth-out is the skin side out;
rough-out is 'inside out' if you will. Smooth-out is more stylish but less
resistant to abrasion. If you want to look really cool at the ski lodge and
limit your hiking to gentle trails, get smooth-out.
The upper is then attached to the sole. This is called 'welting,' and can be
done in a variety of ways. The two basic styles of welting are 'turned in' and
'turned out.' On cheaper boots, the welting is done by vulcanizing (heat).
Moving up, the best price/performance is welting with cement (an impressive
euphemism for glue). The top of the ladder is welting by stitching the upper
to the insole, and some employ stitching and cementing.
The part of the sole that your foot touches is the insole. The part under that
is the midsole, which today is often made of foam. The bottom is the outsole.
The harder the outsole material, the better it is for dirt and grass. A
softer outsole is better for rock...pick your poison based on your hiking
preferences, or if you can afford it, own a pair for each.
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