Dead Reckoning versus Terrain Association

Posted: 12/24/2014 in Land Navigation

When moving from A to B, what land nav. movement method should you use and why?

Dead reckoning (actually Deductive reckoning) is the method normally used when moving in very low light conditions such as heavy rain, fog, snow or at night. Also when moving through very thick vegetation, such as thick forest or dense jungle, or an area with very few recognizable terrain features, such as prairie or very flat desert. It would also be used if moving from an attack point very near an objective to ensure you don’t miss it.

Dead reckoning involves first determining, on your map, your current location, then the distance and azimuth (bearing) to your objective. The azimuth is dialed into your compass, rotate your body until your north seeking arrow is aligned (RED IN THE SHED) and start walking, keeping your pace count and red in the shed, until you reach your objective. Dead reckoning is usually not as accurate as terrain association and you must constantly update your location on your map, while keeping separate track of distance and azimuth changes, if any, about once every 30 minutes. You might also have to cross terrain that you would avoid during a daytime movement. The longer the movement the larger error involved so, if possible, break the overall movement into several short legs with multiple en route check or way points. During night navigation, you must illuminate your compass dial without ruining your night vision and/or compromising yourself in the process. Hold your compass and flashlight under your poncho or shirt for a minute or so. During a night movement, your rate of travel will be much slower than during a day movement, and your stride will be shorter, affecting your pace count.

Keeping your pace count is important when using dead reckoning. One device used to record your pace are Ranger Beads. Here is a link to a photo and explanation of how to make your own. You can also find them, ready-made, online.  http://lifehacker.com/5850246/make-and-use-ranger-beads-to-measure-your-walking-distance . I keep a set in my map case and use them when navigating using dead reckoning. They’re basically beads, strung on a piece of gutted 550 cord, nine beads below a knot, four above it. Each bead on the bottom represents 100 meters. Each bead at the top represents 1,000 meters or 1 kilometer (1 click). For every 100 meters you count using your pace count, pull a 100 meter bead up, after you have traveled 1 click, pull the nine beads back down to reset and pull one 1 kilometer bead up. After 5 clicks, start them over. Not rocket science but they work.

When planning a movement using this method, it’s best to plan for several check points along the way. Good check points include linear man-made and natural terrain features that you will intersect on your azimuth such as, roads or trail crossings, streams, and ridgelines or valleys that you would not miss in the dark. They can also be used as a backstop to warn you have passed your objective. When planning your route using your map, measure off the distance to each en route checkpoint, note them and check each off as you reach them, noting them on your map as your current location.

Map features pitfalls. You can usually rely on natural terrain features being exactly where they are shown on the map. I say usually, with the exception of Ft. Drum, NY. When stationed there as a new infantry private, land nav. could be pretty frustrating. More often than not, when conducting a movement, we would walk directly into a new beaver pond or marsh that, of course, was not on the map. They seemed to number in the hundreds and they constantly popped up in new locations. It could be frustrating but we got pretty good at navigating around them while not getting off azimuth and losing our pace counts. Man made features, however, can get you in a boat-load of trouble. Structures are torn down and new ones are built. New roads are paved, and anybody with a four-wheel drive truck can rough-in a new dirt road. Old logging or forest service roads are neglected and can grow over. Depending on the age of the map, areas that are shown as forested have been logged and areas that are shown as a clearing are overgrown. My best advice is to look for man-made features such as paved roads, dirt roads and clearings on your map anyway, measure the distance to them and, as you get closer to the checkpoint, slow down and start looking closely for that road bed or newly planted area. If you find it great, note it on your map. If you don’t find it, go on to the next checkpoint. If you happen upon a dirt road or other feature that’s not on the map, you can make a notation for future use. Our maps, of the AO we operate in, have been updated in this manner. Again, always keep track of your current location as you move. If you find you are lost, dial a 180 degree reversal into your compass, and return on the back azimuth, using your current pace count, back to your previously known checkpoint.

Offsets:  When dead reckoning to your objective, try to intentionally offset to one side or the other of the objective along a linear feature, such as a stream or road, so that you will know to move left or right to the final objective, or checkpoint, once you reach the feature.

Attack points:  Use easy to find terrain features, that are in close proximity of your final objective, to get you close to your objective. Examples include road/stream intersections.

Handrails:  Rather than walking on roads, ridgelines, next to streams, in valleys or any other linear feature, move parallel to it, just within eyesight, dependant on cover and concealment. This technique is not only tactically significant to a small unit, but sometimes movement is easier, faster, and quieter while hand railing along a stream rather than through thick vegetation, loose slippery rocks and water in the stream bed not to mention the risk of skylighting when walking a ridgeline, or compromise if walking a road, which is a linear danger area and high-speed avenue-of-approach combined.

Terrain association is the always the preferred method of movement, when environmental conditions permit. Again, determine your present location on your map by triangulation, orient the map to the terrain around you, then determine an azimuth to your objective. Using terrain analysis with your map, you might determine that a direct azimuth route-of-march is not the best course while taking advantage of the terrain to make your movement easier or to mask your movement. You may plan a circuitous route, using several different terrain features along the way to guide you and to use as en route checkpoints/waypoints. I would recommend that you determine a general azimuth for each leg but it’s not necessary, since you can always triangulate to visible terrain features along the way. Again, keep your map location updated as you move. Once you are close to your objective, you can switch to dead reckoning from a nearby attack point to guide you precisely to the target.

I found a video on YouTube that you might find interesting. The author covers many areas listed above and is professionally done.

 

 

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