INTRODUCTION TO LAND NAVIGATION - University of Akron

1 Section5 Key Points1 Understanding Azimuths2 Converting Azimuths 3 Determining Elevation 4 Calculating Distance on a MapINTRODUCTION TOLAND NAVIGATIONT actics andTechniques Track8420010_TT5_p198-213 8/19/08 10:59 AM Page 198 Tactics andTechniques TrackIntroductionTo accomplish your mission, you must be in the right place at the right time. Being inthe right place requires you to navigate well. Knowing how to read a map is onething knowing how to use a map to navigate requires that you understand how touse azimuths, elevation, and map distance. In the previous section, you learned how to identify and interpret topographicsymbols, colors, contour lines, and marginal information found on a military map. Youalso learned about the military grid reference system and how to plot grid coordinatesusing a military map and protractor. This section will expand your map-reading skills and introduce you to how themilitary navigates using a map, compass, and protractor.

2 You will learn what anazimuth is and how to convert azimuths in order to navigate using a compass andmap. You will also learn how to determine the elevation of the terrain by analyzing thecontour lines and contour interval data from the marginal information on a militarymap. Lastly, you will learn to compute straight-line and road distance using the scale inthe margin of the military map. Coupled with your learning from your orienteeringand map reading lessons, you will have the basic knowledge to navigate from onepoint to another and arrive safely at your destination. In the following vignette, COL John Zierdt Jr., commander of the 1st SupportCommand during the first Gulf War, remembers how a group of Soldiers paid a seriousprice when they decided to rely on familiarity rather than put into practice basic map-reading and land- NAVIGATION skill required of all Soldiers. Captured During Desert StormThe driver had been on a particular route two or three times and thought heknew where he was going.

3 Then instead of turning left, he kept going even saw the water on their right, which was a dead giveaway that theywere going north rather than west. There were two HETs [heavy trucks] followingeach other. The guy, the one that was eventually captured, was in the leadvehicle, and stopped. And the guys behind him said, You re going the wrongway and we need to turn around. He said, I am not. He says, I m goingstraight. You can follow me or turn around if you want. So, they kept going straight. The next thing you knew they were in the middleof a firefight. The second vehicle got turned around in time [and] got out ofthere; the [first] vehicle got stuck and didn t get turned around, and the two ofthem got captured. Department of the Army, XVIII Airborne Corps and US Army Center of Military History INTRODUCTION to Land NAVIGATION 1998420010_TT5_p198-213 8/19/08 10:59 AM Page 199 Understanding AzimuthsEverything in land NAVIGATION begins with an azimuth.

4 An azimuth is a horizontal anglemeasured clockwise by degrees or mils between a reference direction and a line to anobserved or designated point. There are three base directions or azimuths: true, grid, Army uses azimuths to express direction. Direction is determined from yourstart point, or where you are, outward toward your desired destination, or your intendedtarget. Because you use north (0 or 360 degrees) as your base line, 270 degrees away fromnorth will always be due of yourself as standing in the middle of a Nebraska cornfield. You are facingnorth. The horizon stretches around you in a great 360-degree circle. If you travel anazimuth of zero degrees or 360 degrees or due north you will wind up in you turn to your right and travel on an azimuth of 90 degrees due east you willwind up in the Atlantic Ocean, probably off the coast of New azimuth of 180 degrees due south will take you into Mexico, and an azimuthof 270 degrees due west will take you to the Pacific, just off the coast of a Grid Azimuth Using a ProtractorThere are two ways you can determine an azimuth.

5 You can use a map to determine agrid azimuth, or you can use a compass to determine a magnetic azimuth. Regardless ofthe technique, you will learn in this chapter how to convert a grid azimuth to a magneticazimuth and a magnetic azimuth to a grid azimuth. You will first use a map and learnhow to determine a grid azimuth. The steps in this process should be very familiar if youhave ever taken a geometry begin, select a start point on the map. Mark it as point A. Identify an end point onyour map. Mark it as point B. Using the edge of your protractor, draw a straight pencilline between points A and B. The line is your azimuth. Now you must determine the gridazimuthof that line the angle between the line and grid you lay your protractor down on your map, make sure you place it right sideup; verify this by checking to see that the writing on the protractor is not backward. If yourprotractor is wrong side up, you will get grid azimuths that are 180 degrees off from the200 SECTION 5 The terms ThinkingIf the drivers of the two vehicles had looked at and oriented their maps, whatmight have told them they were headed in the wrong direction?

6 What would you have done if you were in the second vehicle? Would youhave continued to follow the first vehicle after you decided it was going thewrong way?What could you have said over the radio to the Soldiers in the first vehicle thatmay have triggered in their minds that they were, in fact, going in the wrongdirection?eazimuththe horizontal angle,measured clockwise bydegrees or mils betweena reference directionand the line to anobserved or designatedpoint there are threebase (reference)directions or azimuths:true, grid, and magneticazimuthgrid azimuththe angle between gridnorth and a line drawnon the map8420010_TT5_p198-213 8/19/08 10:59 AM Page 200 Figure Protractor (GTA 5-2-12, 1981) INTRODUCTION to Land NAVIGATION 201correct grid azimuth. Also, make sure the 0- or 360-degree mark of your protractor istoward the top (or north) of your map, and make sure the 90-degree mark is toward theright (or east) of your you place your protractor down incorrectly on your map, thegrid azimuth that you determine will be a minimum of 90 degrees off and as much as 270degrees off the actual these three steps to determine your grid azimuth from the arbitrary points Aand B (Figure ) the index of your protractor (the place where the etched vertical line andthe etched horizontal line meet) at the point where the line you drew on yourmap crosses a vertical, north-south grid the index at this point, line up the 0-to-180-degree line, or base line, ofthe protractor on the vertical, north-south grid your line outward to the degree scale of your protractor.

7 Read the valueof the angle from the protractor. This is your grid azimuth from point A to pointB expressed in , you will plot an azimuth from a known point on a map. Imagine you receive anorder to move from your current position in a given direction. Plotting the azimuth onyour map will allow you to see the terrain and objects you will need to navigate throughalong the entire length of your azimuth. The steps are as follows:Although having themils scale on the outsideof the protractor mayseem confusing now,don t get into the habitof cutting the mils scaleoff your protractor. Laterin your military career,your militaryoccupational specialty(MOS) may require youto state azimuths inmils as well as 8/19/08 10:59 AM Page your protractor on the map with the index mark at the center of theknown point and the base line parallel to a vertical, north-south grid your pencil, make a small tick mark on the map at the edge of theprotractor at the desired azimuth.

8 Remember that your protractor will havedegrees on the inner scale and mils on the outer scale. Ensure the tick mark onthe map is beside the desired azimuth in degrees and not and reposition the protractor so you can use its side as a straightedge. Drawa line connecting the known point and the tick mark on the map. This is yourgrid direction line your SECTION 5 Figure an AzimuthThis is the same methodyou will use todetermine the gridazimuth between anytwo points on the 8/19/08 10:59 AM Page 202 Determining a Back Azimuth A back azimuthis simply the opposite direction to your azimuth. A simple example iswhen you get on the interstate going north when you wanted to go south. At the nextexit, you get off the interstate, turn around, and get back on the interstate going south. Youjust took a back azimuth, or in slang, you just did a 180. To compute a back azimuth from an azimuth, simply add or subtract 180 degrees toor from your original azimuth.

9 Remember that a circle has 360 degrees, so if your azimuthis greater than 180 degrees, adding 180 degrees to determine your back azimuth will giveyou an azimuth that is more than 360 degrees. For example, if your azimuth were 200degrees, adding 180 degrees would result in a back azimuth of 380 degrees, whereassubtracting 180 degrees would result in a back azimuth of 20 degrees. The back azimuth380 degrees is obviously greater than the number of degrees in a circle 20 degrees , you could subtract 360 degrees from 380 degrees and still get the same correct backazimuth of 20 degrees. But this simply adds another step to the process. So, subtracting180 degrees from azimuths greater than 180 degrees simplifies determining back a Magnetic Azimuth to an ObjectA magnetic azimuthis an azimuth determined using magnetic instruments, such as acompass. The Army uses two types of compasses: the M2 compass and the lensatic use the M2 compass primarily for positioning indirect fire weapons such as lensatic compass, pictured in Figure , is the compass the Army uses for determine a magnetic azimuth using a your compass to its fullest so the cover forms a straightedge with the the lens (the rear sight ) to the rearmost position.

10 This allows the dial tofloat your thumb through the thumb loop, form a steady base with your thirdand fourth fingers, and extend your index finger along the side of the the thumb of your other hand between the lens (rear sight ) and the bezelring; extend your index finger along the remaining side of the compass, and yourremaining fingers around the fingers of your other hand. Tuck your elbows intoyour sides. This will place the compass between your chin and your your body toward the object that you wish to get an azimuth to, pointingyour compass cover directly at the down and read the azimuth from beneath the fixed black index line on thecompass to Land NAVIGATION 203back azimuth the opposite direction ofan azimuth to obtaina back azimuth from anazimuth, add 180degrees if the azimuth is180 degrees or less, orsubtract 180 degrees ifthe azimuth is 180degrees or moreCritical Thinking1. Why is it important for you to understand how to determine a back azimuth?