Terrain Association - Navigation Methods
116. NAVIGATION METHODS
Staying on the route is accomplished through the use of one or two navigation techniques-dead reckoning and terrain association. Each method will now be discussed in detail.
a. Moving by Dead Reckoning. Dead reckoning consists of two fundamental steps. The first is the use of a protractor and graphic scales to determine the direction and distance from one point to another on a map. The second step is the use of a compass and some means of measuring distance to apply this information on the ground. In other words, it begins with the determination of a polar coordinate on a map and ends with the act of finding it on the ground.
(1) Dead reckoning along a given route is the application of the same process used by a map maker as he establishes a measured line of reference upon which to construct the framework of his map. Therefore, triangulation exercises (either resection or intersection) can be easily undertaken by the navigator at any time to either determine or confirm precise locations along or near his route. Between these positionfixes, your location can be established by measuring or estimating the distance travelled along the azimuth being followed from the previous known point. You might use pacing, a vehicle odometer, or the application of elapsed time for this purpose, depending upon the situation.
(2) Most dead reckoned movements do not consist of single straightline distances because you cannot ignore the tactical and navigational aspects of the terrain, enemy situation, natural and manmade obstacles, time, and safety factors. Another reason most dead reckoning movements are not single straightline distances is because compasses and pacecounts are imprecise measures. Error from them compounds over distance; therefore, you could soon be far afield from your intended route even if you performed the procedures correctly. The only way to counteract this phenomenon is to reconfirm your location by terrain association or resection. Routes planned for dead reckoning will generally consist of a series of straightline distances between several check points with perhaps some travel running on or parallel to roads or trails.
(3) There are two advantages to dead reckoning. First, dead reckoning is easy to teach and to learn. Second, it can be a highly accurate way of moving from one point to another if done carefully over short distances, even where few external cues are present to guide the movements.
(4) Never walk with your compass open and held in front of you to move during daylight across open country along a specified magnetic azimuth. The compass will not remain steady or level, and it will not provide you with the most accurate readings when used this way. Instead, you must begin at the start point, face with your compass in the proper direction, sight on a landmark that is located on the correct azimuth to be followed, close your compass, proceed to that landmark, and repeat the process as many times as is necessary to complete that particular straightline segment of the route.
(5) The landmarks selected for this purpose are called steering marks, and their selection is crucial to success in dead reckoning. Steering marks should never be determined from a map study. They are selected as the march progresses and are commonly on or near the highest points you can see along the azimuth line you are following when they are selected. They may be uniquely shaped trees, rocks, hilltops, posts, towers, buildings--anything that can be easily identified. If you do not see a good steering mark to the front, you might use a back azimuth to some feature behind you until a good steering mark appears out in front. Characteristics of a good steering mark are:
(a) It must have some characteristics about it, such as color, shade of color, size, or shape (preferably all four), that will assure you that it will continue to be recognized as you approach it.
(b) If several easily distinguished objects appear along your line of march, the best steering mark will be the most distant object. This will enable you to travel farther with fewer references to the compass. If you have many options, select the highest object. A higher mark is not as easily lost to sight as is a lower mark that blends into the background as you approach it. A steering mark should be continuously visible as you move toward it.
(c) Steering marks selected at night must have even more unique shapes than those selected during daylight. As darkness approaches, colors disappear and objects appear as black or gray silhouettes. Instead of seeing shapes, you begin to see only the general outlines that may appear to change as you move and see the objects from slightly different angles.
(6) Dead reckoning without natural steering marks is used when the area through which you are traveling is devoid of features, or when visibility is poor. At night, it may be necessary to send a member of the unit out in front of your position to create your own steering mark in order to proceed. His position should be as far out as possible to reduce the number of chances for error as you move. Armandhand signals or a radio may be used in placing him on the correct azimuth. After he has been properly located, move forward to his position and repeat the process until some steering marks can be identified or until you reach your objective.
(7) When handling obstacles/detours on the route, follow these guidelines:
(a) Whenever an obstacle forces you to leave your original line of march and take up a parallel one, always return to the original line as soon as the terrain or situation will permit.
(b) To turn clockwise (right) 90°, you must add 90° to your original azimuth. To turn counterclockwise (left) 90° from your current direction, you must subtract 90° from your present azimuth.
(c) When making a detour, be certain that only paces taken toward the final destination are counted as part of your forward progress. They should not be confused with the local pacing that takes place perpendicular to the route in order to avoid the problem area and in returning to the original line of march after the obstacle has been passed.
(8) Sometimes a steering mark on your azimuth of travel can be seen across a swamp or some other obstacle to which you can simply walk out around. Dead reckoning can then begin at that point. If there is no obvious steering mark to be seen across the obstacle, perhaps one can be located to the rear. Compute a back azimuth to this point and later sight back to it once the obstacle has been passed in order to get back on track.
(9) You can use the deliberate offset technique. Highly accurate distance estimates and precision compass work may not be required if the destination or an intermediate checkpoint is located on or near a large linear feature that runs nearly perpendicular to your direction of travel. Examples include roads or highways, railroads, power transmission lines, ridges, or streams. In these cases, you should apply a deliberate error (offset) of about 10° to the azimuth you planned to follow and then move, using the lensatic compass as a guide, in that direction until you encounter the linear feature. You will know exactly which way to turn (left or right) to find your destination or checkpoint, depending upon which way you planned your deliberate offset.
(10) Because no one can move along a given azimuth with absolute precision, it is better to plan a few extra steps than to begin an aimless search for the objective once you reach the linear feature. If you introduce your own mistake, you will certainly know how to correct it. This method will also cope with minor compass errors and the slight variations that always occur in the earth's magnetic field.
(11) There are disadvantages to dead reckoning. The farther you travel by dead reckoning without confirming your position in relation to the terrain and other features, the more error you will accumulate in your movements. Therefore, you should confirm and correct your estimated position whenever you encounter a known feature on the ground that is also on the map. Periodically, you should accomplish a resection triangulation using two or more known points to pinpoint and correct your position on the map. Pace counts or any type of distance measurement should begin anew each time your position is confirmed on the map.
(a) It is dangerous to select a single steering mark, such as a distant mountaintop, and then move blindly toward it. What will you do if you must suddenly call for fire support or a medical evacuation? You must periodically use resection and terrain association techniques to pinpoint your location along the way.
(b) Steering marks can be farther apart in open country, thereby making navigation more accurate. In areas of dense vegetation, however, where there is little relief, during darkness, or in fog, your steering marks must be close together. This, of course, introduces more chance for error.
(c) Finally, dead reckoning is timeconsuming and demands constant attention to the compass. Errors accumulate easily and quickly. Every fold in the ground and detours as small as a single tree or boulder also complicate the measurement of distance.
b. Moving by Terrain Association. The technique of moving by terrain association is more forgiving of mistakes and far less timeconsuming than dead reckoning. It best suits those situations that call for movement from one area to another. Once an error has been made in dead reckoning, you are off the track. Errors made using terrain association are easily corrected, however, because you are comparing what you expected to see from the map to what you do see on the ground. Errors are anticipated and will not go unchecked. You can easily make adjustments based upon what you encounter. After all, you do not find the neighborhood grocery store by dead reckoning--you adjust your movements according to the familiar landmarks you encounter along the way. Periodic position-fixing through either plotted or estimated resection will also make it possible to correct your movements, call for fire, or call in the locations of enemy targets or any other information of tactical or logistical importance.
(1) Identifying and locating selected features. Being able to identify and locate selected features both on the map and on the ground is essential to your success in moving by terrain association. The following rules may prove helpful.
(a) Be certain the map is properly oriented as you move along your route and use the terrain and other features as guides. The orientation of the map must match the terrain or you will become completely confused.
(b) To locate and identify features being used to guide your movement, look for the steepness and shape of the slopes, the relative elevations of the various features, and the directional orientations in relation to your own position and to the position of the other features you can see.
(c) Make use of the additional cues provided by hydrography, culture, and vegetation. All the information you can gather will assist you in making the move. The ultimate test and the best practice for this movement technique is to go out in the field and use it. The use of terrain, other natural features, and any manmade objects that appear both on the map and on the ground must be practiced at every opportunity. There is no other way to learn or retain this skill.
(2) Using handrails, catching features and navigational attack points. First, because it is difficult to dead reckon without error over long distances with your compass, the alert navigator can often gain assistance from the terrain.
(a) Handrails are linear features like roads or highways, railroads, power transmission lines, ridgelines, or streams that run roughly parallel to your direction of travel. Instead of using precision compass work, you can rough compass without the use of steering marks for as long as the feature travels with you on your right or left. It acts as a handrail to guide the way.
(b) Second, when you reach the point where either your route or the handrail changes direction, you must be aware that it is time to go your separate ways. Some prominent feature located near this point is selected to provide this warning. This is called a catching feature; it can also be used to tell you when you have gone to far.
(c) Third, the catching feature may also be your navigational attack point; this is the place where area navigation ends and point navigation begins. From this last easily identified checkpoint, the navigator moves cautiously and precisely along a given azimuth for a specified distance to locate the final objective. The selection of this navigational attack point is important. A distance of 500 meters or less is most desirable. Terrain association navigation.
(3) Recognizing the disadvantages of terrain association. The major disadvantage to navigation by terrain association is that you must be able to interpret the map and analyze the world around you. Recognition of terrain and other features, the ability to determine and estimate direction and distance, and knowing how to do quickinthehead position fixing are skills that are more difficult to teach, learn, and retain than those required for dead reckoning.
c. Combination of Techniques. Actually, the most successful navigation is obtained by combining the techniques described above. Constant orientation of the map and continuous observation of the terrain in conjunction with compassread azimuths, and distance traveled on the ground compared with map distance, used together make reaching a destination more certain. One should not depend entirely on compass navigation or map navigation; either or both could be lost or destroyed.