Tag Archives: mgrs

Origins of the Military Grid Reference System

Posted on by
1

Several weeks ago John Carnes, owner of the Maptools.com website, contacted me with some additional information regarding the origins of the Military Grid Reference System (MGRS). It appears John has a friend who had some interest in the origins of MGRS and back in 1994 contacted the Defense Mapping Agency looking for information.

John Hager, a geodesist with DMA, responded with a detailed letter and references tracing the history and origins of MGRS. John Carnes has taken this information and created a very informative page on his website. I encourage you all to go to John’s MGRS history page and read up on the history of MGRS and review the links he provides. There’s a lot of great historical information there!

Some points and observations I gleaned from reviewing the documents:

  • The Universal Transverse Mercator Grid system (UTM) was developed far earlier than I thought. Based on my previous reading I thought that UTM had been developed by the Army Map Service specifically to support the development of a world-wide grid reference system like MGRS. However, it appears that the U.S. Army adopted UTM in 1937, years before the creation of the Army Map Service.
  • The original MGRS structure as proposed in 1948 had it covering globe in an area from 80° north latitude to 80° south latitude. Above and below 80° the polar regions were to be covered using the Universal Polar Stereographic (UPS) coordinate system. However, some time after 1948 the MGRS coverage was extended to cover up to 84° north latitude. MGRS was extended into this region as a reflection of NATO’s anticipation of having to fight a ground war with the Soviet Union in arctic regions.
  • There’s a lot of concern expressed by a lot of people in these documents regarding grid zone intersections, or ‘zippers’ as we referred to them. Everyone understood these grid zone intersection areas posed critical challenges and demanded extra caution when directing operations that crossed an intersection boundary. In fact, the issue so concerned the British that they expressed a preference for a less accurate ‘mesh’ grid system that would eliminate grid zone intersections altogether. One of the reasons UTM was selected as the foundation to build MGRS on is because its narrower 6° wide zones introduced less error in these intersection areas.
  • As good as the UTM/MGRS system was (and still is) the fact that it had to be built on ‘local’ datums like NAD27 (in the US), ED50 (in Western Europe) or the Tokyo Datum (in Korea) quickly revealed the need for a world-wide datum, one that was equally good (or as one of my survey instructors put it, “equally poor”) across the globe. This need led directly to the World Geodetic System of 1984, or WGS84, the datum on which all US and NATO military maps are currently based.

So put your geo-geek cap on, head over to John’s website and read up on the origins of MGRS. These documents outline the background of the grid system many of us have a love-hate relation with, yet it’s a grid system that has stood the test of time in places like Europe, Korea, Vietnam, Kuwait, Iraq and Afghanistan, and is now adopted for official use here in the United States as the US National Grid.

– Brian

Right Under My Nose The Whole Time

Posted on by
2

As many of you know, I’ve been scratching around for some time trying to dig up the origins of the Military Grid Reference System (MGRS). I recently became interested in it in light of the fact that the US Geological Survey and Department of Homeland Security have adopted MGRS as the grid standard for the continental US (they’re only 60 years late, but who’s counting!).

I had some old friends at Fort Bragg who are involved in the mapping & charting field root around and they came back with the opinion that development of MGRS was likely tied to NATO and NATO standard agreements (STANAGs as we used to call them). There is probably some truth to that, but there were still several pieces of the puzzle missing. One of those was just when the US Army adopted MGRS.

For the past several months I’ve been scouring eBay, purchasing early copies of US Army map reading and land navigation manuals. The first official, general issue map reading manual came out in 1938 (Basic Field Manual Volume 1, Chapter 5, Map and Aerial Photograph Reading) and was quickly followed by updates in 1941 and 1944 as FM 21-25.

Tucked away in the back of my 1944 copy of FM 21-25, Elementary Map and Aerial Photograph Reading were two changes that I never paid much attention to. ‘Changes’ in Army parlance were updates to manuals or other documents. The Army would publish a change in the form of an addendum and distribute it throughout the Army. It was the individual unit’s job to make sure all the changes were ‘posted’ (this usually meant you physically attached the change document to the base document by some means, like stapling). That’s how the military managed publication changes before this internet thingey came along.

Today I was giving this manual a close read and decided to pay attention to the change documents. To my surprise one of the changes (Change 2) was dated November 1950 and was summarized as follows:

“Principal changes are in methods of giving grid references. These changes are made to comply with AGAO-S 061.3 (28 Dec 49) CSGID-M, dated 29 December 1949, which establishes the MILITARY GRID REFERENCE SYSTEM as official for the Department of the Army”

So there you have it. The Army adopted MGRS in December 1949. Part of the mystery solved!

So now I know the why and the when. What’s still missing is the how.

MGRS is based on the Universal Transverse Mercator Grid (UTM), which was developed by the Army Map Service sometime right after WWII.  What I need to find now is the original description of UTM and MGRS, the document prepared by the Army Map Service describing how MGRS is calculated and constructed, and how it should be implemented.

My guess is that these founding documents are buried deep in the archives of the National Geospatial-Intelligence Agency (the descendant of the Army Map Service).

Anybody know someone at NGA who can spend a lunch hour digging around for this info?

– Brian

US Army FM 21-26

Posted on by
Reply

An Army field manual as a book of the month?  Just how interesting or relevant or important can a field manual be?

Well follow along, because for certain groups of people this FM is very interesting, relevant and important.

FM 21-26, Map Reading and Land Navigation is the Army’s map reading and land navigation handbook.  This manual has been in continuous publication and upgrade since 1941.  The current edition is dated 2005, with changes posted in 2006.  As part of a sweeping Army field manual re-designation the manual has been renamed FM 3-25.26*.  Regardless, it is still commonly referred to as FM 21-26, and that’s how we’ll refer to it here.

The Army seems to have adopted standard map reading and land navigation practices back in 1939, and published its first series of map reading and land navigation manuals in early 1941 (FM 21-25, Elementary Map and Aerial Photograph Reading and FM 21-26, Advanced Map and Aerial Photograph Reading).  Prior to 1939 map reading and land navigation was viewed almost as a black art, covered in non-standard texts targeted at officers and emphasizing field sketching and rudimentary survey as much as map reading and navigation.  A large part of the problem was that the Army had no map standards or centralized map production, so providing maps for unit operations was a local commander’s headache.  If you were a regimental commander and wanted a map of an area you put your regimental engineers to work either finding suitable maps from local or commercial sources, or you had them drawn up from field sketches or plane table surveys.

Army leaders realized that in the looming global war the old ways of producing and using maps would not do.  The Army needed dedicated map production assets that could produce millions of maps using common symbols, colors and scales.  This led to the creation of the Army Map Service and the standardization of map production on a global scale.  Once you had map standards in-place and maps in production you could develop standardized map reading and land navigation practices using these new maps.  FMs 21-25 and 26 were the result of that effort.  Finally, the Army had standardized map reading and land navigation texts it could use to train the millions of Soldiers about to be drafted into the Army to fight WWII.

After WWII, the establishment of NATO and the US Army’s realization that it would still maintain global warfighting responsibility the two field manuals were combined into one – FM 21-26, Map Reading, published in 1956.  The significant change in this manual was the introduction of the Military Grid Reference System (MGRS) based on the Universal Transverse Mercator (UTM) coordinate system.  The development of UTM and MGRS signified a revolution in mapping and mapping grids.  For the first time an army had an accurate low distortion world-wide grid system suitable for large scale mapping.  With MGRS and using just a paper map and a simple protractor a Soldier could uniquely identify his position anywhere on the face of the earth to within 10 meters.  MGRS is accurate, easy to teach, easy to use and virtually ‘soldier-proof’.

Updates to FM 21-26 came out every few years and the major changes seem to have been the simplification of basic principles and techniques, and the dropping of out-of-date or no longer needed procedures (like interpreting hatching to indicate landforms or the use of obsolete equipment).

Today’s FM 21-26 is map reading and land navigation distilled down to the basic, easy to learn and easy to execute functions.  It is not just map reading, but it is also the use of map substitutes (mainly aerial and satellite images), dead reckoning, field expedient direction finding, basic orienteering, terrain association and basic field sketching.  One key item of note is the Army’s method of teaching how to determine the magnetic to grid declination factors.  The lesser or greater angle method is hands down the easiest way to manage this often confusing issue.

Sure, FM 21-26 has a military focus.  It is, after all, an Army field manual.  The book spends a lot of time discussing the use of the MGRS system, how to orient, plan and navigate using MGRS.  It’s MGRS, MGRS, MGRS.  For years civilian students of map reading and land navigation had no use for this portion of the manual.  Topographic maps of the US either had no grids or had grids different than the MGRS grid, and US-based maps were printed at scales different than those used by the military.  This has all changed.  In just the past few years the US has (finally!) adopted what is known as the US National Grid.  The US National Grid is now being implemented for all USGS (US Geological Survey) large scale (1:24,000 and 1:100,000) topographic line maps, and the USGS is rushing the new US Topo series of maps into production.  So what is this new US National Grid?  It is nothing more than MGRS implemented for all USGS topgraphic maps of the US.  Remember, MGRS has always covered the world, but the US military does not produce maps of the US – that’s the job of the USGS.  The MGRS grid template always existed for the US, but the USGS never adopted it.  Until 2008, that is.  Driven by homeland security and disaster relief coordination concerns the USGS formally adopted MGRS, known as the US National Grid in the US, and is now producing maps to that standard.

Suddenly the discussion of MGRS in FM 21-26 becomes very relevant.  All the MGRS-based map reading techniques can now be directly applied (and are intended to be applied) to the new USGS topographic maps.  The only remaining issue is that of scale.  The US military produces large scale maps at 1:50,000 while the USGS produces large scale maps at 1:24,000.  While all the MGRS techniques apply to USGS maps, you can not use the standard map protractor (GTA 5-2-10) discussed in FM 21-26 since it does not have a 1:24,000 plotting scale included.  This isn’t a real problem because a number of manufacturers offer MGRS/US National Grid plotting scales for use with 1:24,000 scale maps.  One of my favorites is the Super GTA tool produced by Maptools.com.

Another great thing about FM 21-26 is that it is one of the few Army field manuals authorized for unlimited release.  This means the Army retains the copyright to the manual, but users are free to copy, reprint and distribute it without penalty.  As a result you can find free downloads of FM 21-26 all over the web and you can purchase inexpensive printed copies from retailers like Amazon.com.

So, if you like maps, are interested in map reading and land navigation, or have just a passing interest in these topics go get yourself a copy of FM 21-26!

– Brian

*The new designation of FM 3-25.26 seems a little unusual in the overall scheme of revised manual numbering.  I’d like to think that someone in TRADOC with a respect for military history recognized the significance of the original series of manuals, FM 21-25 and FM 21-26, and as a nod to tradition decided to redesignate the new manual as FM 3-25.26.