9.3 Land Navigation: Terrain Features, Azimuths, Intersection, and Resection

Land Navigation: Terrain Features, Azimuths, Intersection, and Resection

Core Doctrine: Operational maneuver hinges on a Soldier's ability to navigate hostile, unfamiliar terrain under all visibility conditions without reliance on electronic GPS systems. Governed by TC 3-25.26, Soldiers must master the identification of the ten terrain features, expert lensatic compass manipulation, azimuth and back-azimuth calculations, resection, intersection, and tactical movement techniques.

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1. Tactical Terrain Appreciation

Terrain dictates tactical movement, concealment, speed, and fire superiority. An NCO must look at a paper topographic map and mentally visualize the three-dimensional battlefield. Military land navigation categorizes the ground into ten doctrinal terrain features: five major, three minor, and two supplementary features.

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2. The Ten Doctrinal Terrain Features

Every promotion board candidate must know the definitions, ground characteristics, and contour line signatures of all ten features:

Five Major Terrain Features

1. Hill: An area of high ground from which the ground slopes down in all directions. On a map, a hill is depicted by contour lines forming concentric, closed loops; the smallest loop in the center marks the hilltop.
2. Valley: An elongated, reasonably level low-ground corridor bordered on three sides by higher terrain. Valleys frequently contain streams or rivers. Contour lines depicting a valley form broad U-shapes or V-shapes with the closed end pointing uphill / upstream toward higher ground.
3. Ridge: A sloping line of high ground extending across the landscape. The crest of a ridge has higher ground along its centerline and slopes downward on both flanks. Contour lines form U or V shapes pointing away from the highest elevation toward lower terrain.
4. Saddle: A dip or low point between two areas of higher ground along a ridge or between two hilltops. A saddle provides a natural avenue of approach across a ridge. Contour lines form an hourglass or figure-eight pattern with higher ground on opposite flanks.
5. Depression: A sunken low point or sinkhole with higher ground in all directions. On a map, a depression is depicted by closed contour loops with hachure tick marks pointing inward toward lower ground.

Three Minor Terrain Features

1. Draw: A small, less-developed natural stream course or water drainageway running down a hillside. There is essentially no level ground in the bottom of a draw. Contour lines form sharp V-shapes pointing uphill toward higher ground (upstream). (Tactical rule: A draw points up).
2. Spur: A short, continuously sloping line of higher ground projecting outward from the side of a hill or ridge. Contour lines form U-shapes or V-shapes pointing downhill away from higher ground. (Tactical rule: A spur points down).
3. Cliff: A vertical or near-vertical slope. On a map, contour lines are drawn so close together that they touch, converge, or merge into a single solid line, occasionally with tick marks pointing downhill.

Two Supplementary Terrain Features

1. Cut: A man-made excavation cut through high ground to level an avenue for a road, highway, or railway. Depicted by contour lines running along the cut with tick marks pointing inward toward the roadbed.
2. Fill: A man-made raised embankment across low ground to support a road, highway, or railway. Depicted by contour lines running along the embankment with tick marks pointing outward away from the roadbed.

Comprehensive Terrain Features Reference Table

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3. The Military Lensatic Compass

The standard military lensatic compass is a rugged, non-magnetic precision instrument designed for tactical navigation.

Critical Components

• Cover: Protects the floating dial and contains the sighting wire and two luminous tritium sighting dots for night navigation.
• Base: Houses the floating dial, the bezel ring, the thumb loop, and the fixed black index line.
• Bezel Ring: A ratcheted ring containing 120 clicks when rotated 360 degrees. Each distinct click equals 3 degrees of angular movement, allowing blind azimuth adjustments at night.
• Floating Dial: Mounted on a pivot. Features two concentric angular scales:
  • Inner Scale (Red): Expressed in Degrees (0 to 360°).
  • Outer Scale (Black): Expressed in Mils (0 to 6,400 mils). Mils provide extreme precision for indirect artillery and mortar fire (1 mil subtends 1 meter at 1,000 meters distance).
• Lens: Magnifies the floating dial scale to allow the navigator to read bearings during cheek sighting.

Operational Compass Sighting Techniques

1. Center-Hold Technique:
   • Open the compass fully so the cover and base form a straight, horizontal platform. Fold the thumb loop fully down.
   • Grasp the compass base firmly with both hands, placing thumbs along the sides and index fingers along the forward edges.
   • Pull your elbows tightly against your ribs and position the compass directly in the center of your chest.
   • Look over the top of the compass cover and turn your entire body toward the target. Read the azimuth directly under the fixed black index line.
   • Advantages: Faster to employ, easier to maintain while on the move, highly effective in darkness, and easily operated while wearing a helmet, body armor, and night vision goggles (NVGs).
2. Compass-to-Cheek Technique:
   • Open the compass cover to a 90-degree vertical angle and raise the lens bracket to a 45-degree angle.
   • Place the thumb through the thumb loop and rest the index finger along the base.
   • Raise the compass to the eye, resting the thumb against the cheekbone.
   • Align the sighting notch in the lens bracket with the sighting wire in the cover and the distant target.
   • Glance down through the magnifying lens to read the magnetic azimuth.
   • Advantages: Delivers superior angular precision for long-range sightings, intersection, and resection.

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4. Azimuths and Back-Azimuths

An azimuth is a horizontal angle measured clockwise from a north reference base line. In military navigation, azimuths are read from 0 to 360 degrees.

The 180-Degree Back-Azimuth Rule

A back-azimuth represents the exact opposite direction (180 degrees) of a forward azimuth. It is used to plot reciprocal routes, verify navigation back to a rally point, and conduct resection.

• If the forward azimuth is LESS than 180 degrees: ADD 180 degrees. $\text{Back-Azimuth} = \text{Azimuth} + 180^\circ$ (Example: Forward azimuth = 65°. Back-azimuth = 65° + 180° = 245°).
• If the forward azimuth is GREATER than 180 degrees: SUBTRACT 180 degrees. $\text{Back-Azimuth} = \text{Azimuth} - 180^\circ$ (Example: Forward azimuth = 230°. Back-azimuth = 230° - 180° = 50°).

Board Exam Quick Check: If an azimuth is exactly 180 degrees, adding or subtracting 180 yields either 360° or 0°, which represent the same cardinal direction: North.

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5. Methods of Determining Location

When standard map reading cannot confirm a position, Soldiers employ geometric triangulation techniques:

1. Intersection (Locating an Unknown Distant Point)

Intersection is the method of determining the grid location of an unknown distant point (such as an enemy sniper position, bunker, or vehicle) by sighting azimuths to it from two or more known friendly locations.

• Procedure: Observer A at known Point 1 shoots a magnetic azimuth to the target, converts it to a grid azimuth, and draws a ray on the map. Observer B at known Point 2 shoots an azimuth to the same target, converts to grid, and draws a second ray. The physical intersection of the two lines on the map marks the grid location of the target.

2. Resection (Locating Your Own Unknown Position)

Resection is the method of locating your own unknown position on the map by sighting azimuths to two or more distant, recognizable terrain features that can be identified on the map.

• Procedure: Shoot a magnetic azimuth to distant Landmark A, convert it to a grid azimuth, calculate the back-azimuth, and draw that line from Landmark A back toward yourself. Next, shoot a magnetic azimuth to distant Landmark B, convert to grid, compute its back-azimuth, and draw the line from Landmark B back toward yourself. The point where the two back-azimuth rays intersect on the map is your precise location.

3. Modified Resection (Locating Position Along a Linear Feature)

If you are lost but know you are located along a prominent linear feature (e.g., a road, powerline, canal, or railroad track), you only need one recognizable distant landmark.

• Procedure: Shoot an azimuth to the single distant landmark, convert to grid, compute the back-azimuth, and draw the line on the map. The point where that back-azimuth line intersects your linear feature is your exact location.

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6. Tactical Movement Techniques: Dead Reckoning vs. Terrain Association

Cross-country navigation integrates two complementary techniques:

Dead Reckoning

Moving along a predetermined compass azimuth for a specific distance measured by pace count. Highly reliable in featureless terrain (deserts, dense jungles, open water) or during limited visibility and zero-illumination night movement.

• Pace Count Calibration: Every Soldier must calibrate their individual pace count (the number of double-steps taken to cover 100 meters). An average Soldier averages 60 to 70 paces per 100 meters on flat terrain. Navigators track 100-meter increments using ranger beads (pace count beads) or knots in a cord.
• Pace Count Adjustments: Pace counts lengthen when walking downhill and shorten significantly when traveling uphill, through mud, snow, heavy underbrush, or while carrying combat loads.
• Steering Marks: To avoid drifting, navigators select distant, distinct natural objects (trees, rock faces, hilltops) along the azimuth as intermediate steering marks, moving from mark to mark rather than staring continuously at the compass.

Terrain Association

Navigating by matching features on the ground to contour lines and symbols on the map.

• Handrails: Prominent linear terrain features (highways, ridgelines, streams, power lines) running parallel to the direction of travel used to guide movement.
• Catching Features (Backstops): Distinct linear features lying perpendicular to the direction of travel (e.g., a major river or highway) located beyond the objective that alert the navigator if they have overshot their destination.
• Attack Points: An easily recognizable terrain feature located close to the objective where the unit pauses to transition from rapid terrain association to precise dead reckoning for the final approach.