Locating an Unknown Point by Intersection: Land Nav 101

In our ongoing refresher series of articles dealing with Land Navigation, we’ll move on to another basic skill that all Special Operations candidates should know how to conduct. And they should know this before they attend one of the Selection courses for the different units.

We’re starting with the basics of land navigation, a 101 starter course to refresh the more experienced candidates and give the newer or less experienced troops a starting point to learn the finer points of map reading and land navigation.

It is a good idea for everyone to brush up on all of these skills. As we’ve often said on these pages, the two biggest failure areas for Special Operations candidates are the physical tasks and land navigation. Especially in the Special Forces (SFAS) course. Which leads us to today’s topic.

The Army’s study guide lists the definition of Intersection as the location of an unknown point by successively occupying at least two (preferably three) known positions on the ground and then map sighting on the unknown location. While this may not be a particularly common factor in Selection, it is a skill that every Special Operations trooper should know.

It can be used to locate distant or inaccessible points or objects such as enemy targets, danger areas or new structures that are not on the map sheets. There are two methods of intersection: the map and compass method and the straightedge method.

The Map and Compass method:

• Orient the map using the compass as we discussed in an earlier post
• Locate and mark your position on the map (Always double check)
• Determine the magnetic azimuth to the unknown position using the compass
• Convert the magnetic azimuth to grid azimuth using the declination diagram
• Draw a line on the map (grid azimuth) from your position to the unknown one
• Move to a second and third known point and repeat steps 1, 2, 3, 4, and 5.
• The location of the unknown position is where the lines cross on the map.
• Determine the grid coordinates to the point, preferably an eight-digit grid coordinate

This is the best, most efficient way to get it done. In a tactical situation, you can move to multiple points and get all of the required information to locate and pinpoint the unknown position. This is the much-preferred method than the following one.

The Straight Edge Method:

The straight edge method is used when a compass is not available. For a Special Operations candidate, this method should be used only as a training event. Because a candidate should never be without his compass. If you’re on the course without your compass, woe to you. But for the purposes of our training…

This is how it is conducted –

• Orient the map on a flat surface by the terrain association method, as we’ve discussed here in the previous post
• Locate and mark your position on the map (Always Double check)
• Lay a straight edge on the map with one end at the user’s position (A) as a pivot point; then, rotate the straightedge until the unknown point is sighted along the edge.
• Draw a line along the straight edge
• Repeat the above steps at position (B) and check for accuracy.
• The intersection of the lines on the map is the location of the unknown point (C).
• Determine the grid coordinates to the point, preferably an eight-digit grid coordinate

Obviously, this method isn’t as accurate as the one with the compass but can be used in a pinch. Remember, ensure all of these skills are like second nature to yourself during Selection and you should be in a much better position to succeed. The failure to prepare is the biggest failure for the course and the land navigation course is the least forgiving of all of the courses that you’ll come across.

In our follow-on land navigation pieces, we’ll touch on some of the other skills you may need to brush up on.  Until then, if you have any questions, feel free to email me [email protected] or Tweet them to me (@SteveB7SFG) and I’ll be happy to answer them. Either privately or in a post such as this, but without mentioning anyone’s name of course.

Photo: Army Study Guide, US Army