Land Nav?

[Jason Falla]

(pardon the long post)
Mr. Falla,

I do not have any experience doing night land nav, nor as a forward observer. But from my topography lessons at college, and professional experience in the field of geology, I tend to think that milliradian precision is only to be acquired if using a stable, level position, with a long sighting base and appropriate magnification.

Even if all previous considerations are awfully wrong, math still applies.

A circumference has 360 degrees, 2 Pi radians or 6238 milliradians.
1 milliradian equals 0.00017 degrees, while 1 arc-second equals 0.00027 degrees.
Even if military compasses are divided in 6200 or 6400 mils, the above numbers are correct up to the 5th place.

While I was working at a mine in SE Brazil, the survey crew usually spat out angle measurements that amounted to 2 arc-seconds. And that is with a stable, leveled base and precision instrument, which a compass has not and is not.

Further, the error from a 1-degree off compass reading is in the order of 1,7%. So, for a ded reckon lenght of 1000m, one would veer off-course only 17m.

Considering that one would (presumably) rarely cover that long distance without looking around, that 17m mistake would me corrected long before the end of the 1000m leg.

Also, humans rarely walk in a straight line, and in a wooded area, the total distance, due to walking around trees and other obstruction would probably be much more than those 17m.

Using radians (or mils) does have other advantages, though.
What I know that from a known distance from an object is just a matter of a simple multiplication to get the height or length from said object. If using degrees, one needs to use a trigonometric table before doing said multiplication.
The inverse operation allows to get distance from a known height (or length), and that, AFAIK, is the method used with the mil-dot reticle on rifle scopes.

So, if you prefer the mils, just state so. No need to state the precision, which I hopefully made the case, is only of interest to surveyors and engineers.

Other than what I said regarding the mils, I agree with you.

P.S.: Geologists are well known to be fond of the awkward quadrant compasses...

Pmarc, it's quite clear that you know what you are talking about when it comes to mathematical equations and survey.

The Army uses Mils for many practical uses as 1 mil subtends 1 m at 1000 m. The importance of using this system is to minimize as much error as possible. There have been times during my military career that we needed to move across very featureless terrain for long durations and distances and end up with extreme accuracy by finding very small check points. Our selection course is a good example of this, check points are anywhere from 5 to 12 km apart with nothing but desert and salt bush to content with! This type of terrain can also be found in the frozen areas of the arctic circle. While in Norway we were required to move over featureless terrain for several hours on ski's to reach our destination. When there is a lack of visual aids and reference points, one must rely on bearing and paces in order to maintain extreme accuracy. The mil system allows us to minimize errors created by human error in plotting bearings and compass setting while maximizing accuracy over ground.

When there are terrain features that can be used in the aid of navigation, map to ground, or moving tactically using the ground to your advantage, you are correct in saying that any error would be absorbed by the method of movement. But with such a wide area of operations in which we find ourselves, the mil system is the preferred system.

[pmarc]

There have been times during my military career that we needed to move across very featureless terrain for long durations and distances and end up with extreme accuracy by finding very small check points. Our selection course is a good example of this, check points are anywhere from 5 to 12 km apart with nothing but desert and salt bush to content with!

Hehe, that is what experience brings to the table =]
I have read about that. But not having experienced it, makes it a situation I can not relate.
All my work/play has been in feature packed environments.

I can appreciate the importance of bearing precision in featureless country.

But with such a wide area of operations in which we find ourselves, the mil system is the preferred system.

I completely understand now. Thanks for the kind words.

[Jason Falla]

Hehe, that is what experience brings to the table =]
I have read about that. But not having experienced it, makes it a situation I can not relate.
All my work/play has been in feature packed environments.

I can appreciate the importance of bearing precision in featureless country.



I completely understand now. Thanks for the kind words.

Pmarc, you got it brother! Sometimes it's difficult to relay every bit of information using a forum like this and vital aspects of information can be left out. You are obviously very knowledgable and very skilled at what you do. Keep up the good work!

Take care,

[Lone_Ranger]

When there are terrain features that can be used in the aid of navigation, map to ground, or moving tactically using the ground to your advantage, you are correct in saying that any error would be absorbed by the method of movement. But with such a wide area of operations in which we find ourselves, the mil system is the preferred system.

That makes sense. When the US Army taught me land nav, it was as an E5/Sgt, and they were still mentally fighting the Cold War, and preparing us for operating in Europe. Plenty of terrain features. Sadly, from what I hear, they are not teaching map & compass land nav, on that level anymore. They are relying on GPS.

[Lone_Ranger]

The Military Silva 54B Prismatic Compass does have Tritium and is very good even after quite a while operating at night. If you are conducting night navigation you will have to 'charge' the tritium with a flash of white light from time to time in order to keep the glow nice and bright while moving. Tactically, this was done using a bush hat or under a jacket or similar so not to show any white light.

On the Cammenga Military Lensatic Compass, the one that goes for about $45, is like that. Phosphorescent Illumination that needs to b charged, with a flashlight.

The Cammenga Tritium version, runs about $85, and is self-luminescent. Like night sights. They don't need charged. It will work in complete darkness.

I can't seem to find the Silva Expedition 4 Military, or Silva 4B NATO, for sale, in the states. I can get it on line, but I have to ship from the UK. Same, with the Sunto MB-6 (Recta DP), the Swiss Army Compass.

Other models of both brands are available. It's hard to tell which ones have the necessary features.

What's the difference between a prismatic, lensatic, and a baseplate?

[Lone_Ranger]

Great thread. I am going to have to check out the MGRS maps and see whats up. I was thinking about the compass as well, only as a back up to the GPS. Would a military tritium compass be worth it, or just get a regular compass like the one pictured above? Most of my navigation use has been of the airborne variety but I am interested in developing some Land navigation familiarity as well. Maps and compass as well as GPS useage.

US Army FM3-25.26 Map Reading and Land Navigation
http://www.uvm.edu/~goldbar/FM3_25.26.pdf

Chapter 4-3 explains Military Grid Reference System

[pmarc]

That makes sense. When the US Army taught me land nav, it was as an E5/Sgt, and they were still mentally fighting the Cold War, and preparing us for operating in Europe. Plenty of terrain features. Sadly, from what I hear, they are not teaching map & compass land nav, on that level anymore. They are relying on GPS.

That is unfortunate since it is quite possible to put up a GPS jammer.
I am aware that the military use a different protocol and frequency than civi, but the signal is quite faint.

The receivers 15 years ago had problems with overcast/rainy days, and with the jungle cover too.

I have no doubt that China, Russia, maybe Iran have the means to severely degrade GPS signal. Maybe not countrywide, but they might do for select areas.

[Jason Falla]

On the Cammenga Military Lensatic Compass, the one that goes for about $45, is like that. Phosphorescent Illumination that needs to b charged, with a flashlight.

The Cammenga Tritium version, runs about $85, and is self-luminescent. Like night sights. They don't need charged. It will work in complete darkness.

I can't seem to find the Silva Expedition 4 Military, or Silva 4B NATO, for sale, in the states. I can get it on line, but I have to ship from the UK. Same, with the Sunto MB-6 (Recta DP), the Swiss Army Compass.

Other models of both brands are available. It's hard to tell which ones have the necessary features.

What's the difference between a prismatic, lensatic, and a baseplate?

The Silva 54B has Tritium and is self-luminecent but once you have the compass for several years the tritium begins to get dull and a quick hit of white light brightens it up.

The base plate is good because of the advantages of the on board roamer and ruler.

The 54 series, I believe are prismatic. The B I think refers to the system on the compass card, degrees or Mils. Also make sure that you are buying northern hemisphere version. On the back of the dial there will be small lettering that says MS or MN that denotes what hemisphere you are in. I believe its Meridian North and Meridian South.

The Lensatic compass are issued also to the Australian Army but SOF get the Silva. THe Lensatic is a robust MilSpec compass that has a prism that you can use to sight also. It has a compass card that you can lock down after you take your bearing.

I just prefer the base plate style compass. They both work well, just depends on what you like.

[reccerecon]

The Army still teaches some land nav to everyone at Basic, Combat Arms naturally get a lot more training at OSUT and at their unit. If anyone is wanting a MGRS map they can be custom made by mytopo.com, I've been more then happy with the ones I've had made. As far as I know they are the only place to get MGRS maps, they even have a PC program to make your own. I understand what is being said about using mils, I too have used degrees for almost all land nav. It honestly gives me a headache just thinking about doing the conversions though.

[Deuce]

The Army still teaches some land nav to everyone at Basic, Combat Arms naturally get a lot more training at OSUT and at their unit. If anyone is wanting a MGRS map they can be custom made by mytopo.com, I've been more then happy with the ones I've had made. As far as I know they are the only place to get MGRS maps, they even have a PC program to make your own. I understand what is being said about using mils, I too have used degrees for almost all land nav. It honestly gives me a headache just thinking about doing the conversions though.

I concur, old school land navigation is still alive and well at least among the Infantry. I can't speak for other MOS's but I know I've seen the support guys and gals out there as well. They may not get it as extensively but they're at least given familiarization.

Sent from my SPH-M930BST using Tapatalk