History Revealed! Origins Of The Army Lensatic Compass

For several years I’ve been trying to piece together the history of the US Army’s lensatic compass.  In an earlier post on this blog we discussed the various types of compasses and a bit of the developmental history that can be inferred by viewing the examples in my collection.  However, there was (and still is) very little solid history on the development of the lensatic compass available on the web.

For an item as ubiquitous as this compass the lack of historical data seems a odd.  The development and usage histories of many other items of WWII-era equipment are well documented.  Take the M1 Garand for example.  Collectors can discuss in detail every single part on that rifle and can accurately date and discern the manufacturer of each part by noting subtle differences in how the piece was machined or finished.  This wealth of knowledge is due to the fact that the development and production records for the Garand were made available decades ago by the US military and the various manufacturers.  Of course collector interest is also a factor.  The Garand is one of the most collected pieces of WWII equipment and when you have thousands of collectors clamoring for detailed information the odds are pretty good someone is going to unearth the data.  Since there can’t be more than a dozen serious collectors of Army lensatic compasses there’s a whole lot less clamoring.

As an item of individual equipment that guided millions of Soldiers across the battlefields of Europe and the Pacific in WWII, and continues in use by our Soldiers today, I’ve always felt the history of the lensatic compass deserved better coverage.

Earlier this week I was on a different quest.  I recently purchased an interesting bit of Army topographic kit, a Vertical Sketchmaster (I’ll do a posting on that later).  Since the device came without paperwork or documentation the first thing I did was hit Google for a quick search.

[A short segue here.  Hey Google, your search results are starting to look like those from the half dozen or so search engines that have all but fallen off the internet.  When I do a search on your site I’m looking for real results, not page after page of ads or eBay listings.  Any more, searching on Google is like searching on – dare I say it – Yahoo!]

Buried about three pages deep in the search results was a reference to a holding in the Defense Technical Information Center (DTIC) titled “History of [the] U.S. Army Topographic Laboratories (1920 to 1973)”.

The phrase “Army Engineer Topographic Laboratories” got my immediate attention because the document could only be referring to what used to be know as the Army Corps of Engineers’ Engineer Topographic Laboratories, or ETL.  ETL and it’s predecessor organizations within the Corps of Engineers served (and still serve) as the Army’s R&D lab for development of topographic, terrain analysis and geospatial systems, processes and equipment.  Now called the Army Geospatial Center, it was an organization I called on many times during my career for support and advice, and they always came through.

As luck would have it the document is available in digital form through Google.  I immediately downloaded it and started reading.  Published in 1973 as an ETL internal paper by John Pennington, it is a short rundown of the history of the Army’s topographic R&D labs and covers major projects and equipment development between 1920 and 1970.  I don’t want to spend too much time on this document in this post, because I feel it deserves it’s own separate discussion at a later date.  For now I’ll just say it is a treasure trove of historical information.

While reviewing the document for information on the vertical sketchmaster I quickly came across discussion of lensatic compasses.  This was something completely unexpected.  I never considered that the development of the lensatic compass was something an Engineer topographic R&D lab would have been involved with.  After reading the entries it now makes perfect sense – the Engineers had doctrinal responsibility for development of land navigation equipment and were the Army’s subject matter experts on compasses of all types.  While the development of land navigation techniques including the use of map and compass was the responsibility of the Infantry School, development of the compass as an item of equipment was the responsibility of the Engineers.  Of course the two branches worked hand-in-hand on the project, with the Engineers serving as a test and development agency in support of the Infantry School.

The document briefly discusses compass development both prior to and after WWII and adds some fascinating tidbits to the history of the development the lensatic compass:

Since the quality of the scan is pretty poor I’ve reproduced the key parts below:

(7)  Compasses.  Although the compass is not strictly a surveying instrument, considerable effort was expended by the Mapping Branch of the Engineer Board in the World War II period on the development of small compasses for Infantry and other arms.

The work started in 1938 when the Infantry requested that an inexpensive, commercial-type compass be found to replace the marching compass then issued because the marching compass was too large, elaborate, and costly.  This investigation was assigned to the Engineer Board, and it was soon found that no suitable commercial compass was available.  The W. & L.E. Gurley and the Taylor Instrument Companies, however, were willing to make a suitable compass based on a new design; and each company made six samples in 1939 as ordered from the Engineer Board.

After testing by both the Infantry and Cavalry and some modifications by the manufacturers, in November 1940 the Engineer Board recommended procurement of the cheap lensatic compass from both manufacturers.”

Thus we have the WWII-era M1938 lensatic compass.

M1938 Lensatic Compass
My question now is, was this originally a liquid filled model?  Read below.

One interesting point is that while lensatic compasses made by Gurley are fairly common (they were a major manufacturer of surveying equipment at the time) I have never seen a military lensatic compass made by Taylor Instruments.  However, Taylor Instruments did go on to be a major manufacturer of wrist compasses for the US military in WWII.

But the story is not over.  Even back in 1940 they were struggling with the issue of how to dampen the compass needle or card.

“Since the mechanical dampening arrangements in all compasses available up to that time had not been entirely satisfactory, the Engineer Board started investigations of liquid dampening in December 1941.  Compasses of both the lensatic and the wrist type with liquid dampening were developed, tested, and adopted in the 1941 to 1944 period; and it was thought for a time that the compass problem had been solved.  However, it was discovered that, with temperature changes, an air bubble often developed in the compass capsule which impeded the free movement of the compass needle and affected the accuracy.

In July 1944, the Superior Magneto Corporation, one of the liquid-filled compass suppliers, solved the liquid  dampening problem by applying the induction dampening principle.  The compass body was made of copper which set up an eddy current and magnetic field as the compass needle rotated, thus acting as a drag to dampen the needle oscillation.  Samples were immediately procured and tested.  As a result, the induction dampened wrist compass was standardized in April 1945, and the induction dampened lensatic compass was standardized in May 1945.”

Based on the number of WWII compasses available for sale from auction sites like eBay I think that Superior Magneto was the #1 supplier of lensatic compasses during WWII.  Knowing their core business – the production of magnetos – it makes sense that their engineers would have a clear understanding of the principle of induction and how to apply it to the problem of compass needle dampening.

Today M1938 compasses with induction dampening are easy to identify.  They have a white compass bowl that contains the compass card.  The white bowl is the stamped copper cup that the compass magnet interacts with to slow oscillation.  It is an excellent dampening system and is still used today in US military-issue lensatic compasses.

M1938 Lensatic Compass with induction dampening.
Note the white compass bowl.  This is really a stamped copper cup that interacts
with the north-seeking magnet to reduce oscillation of the compass card.

Let’s skip forward now to the late 1940s, when it was clear that the lensatic compass was in need of an upgrade.

(3)  Compasses.  The development of compasses, both the wrist and the lensatic types, was reopened in 1947 to provide instruments which would overcome the deficiencies noted in those developed during World War II.  Experimental models of the lensatic compass were produced by Taylor Instrument Company, Rochester, New York (Fig. 84), and the Brunson Instrument Company, Kansas City, Missouri.  Both were found to conform to the military characteristics, but the Brunson model was considered superior.  Experimental models of the wrist compass were produced by the Brunson Instrument Company, Kansas City, Missouri (Fig. 85), and were delivered to ERDL in January 1950.  Cold weather tests of the lensatic compass were conducted at Fort Churchill, Canada, and in January 1951 service test models were procured and shipped to service test agencies.  Here again, as with the compass development during World War II, emergency procurement of large quantities of both compasses were made before all testing and development had been completed.

Development of both compasses was completed in 1952.  The lensatic compass was classified as standard type, and the project was closed in November 1952.”

The result of these tests and type classification are the classic M1950 Lensatic Compass, a design still in use today:

M1950 Lensatic Compass produced in 2010 by Cammenga.
Today Cammenga is the sole contractor producing lensatic compasses
for the US military.

The M1950 is still one of the best compasses ever developed, and I consider it the best military compass ever issued to any military anywhere in the world.

The Military Lensatic Compass

I’m going to kick off our formal evaluation of compass accuracy with the a design that has been in continuous use  for over 60 years and has seen use by millions of individuals.  It is perhaps the most tested compass design in history, with documented use in jungle, desert, woodland and arctic environments around the world.  It is tried and true and is one of my favorite compass designs.

It is the US Army’s Model 1950 lensatic compass.

The M1950 compass is a design born of war.  It’s predecessor, the M1938 lensatic compass, was developed and adopted just as WWII opened.  It was a good design that was easy to manufacture.  Equally important, the adoption of the M1938 compass allowed the Army to standardize land navigation training, simplify it and teach it to the millions of young men who were being drafted into the Army and Marines. The experiences of war taught the Army a few things about compass design.  First, it proved that the lensatic compass design was a good one.  It was accurate, reliable and versatile.  With its compass card graduated in both degrees and mils it was usable by the both infantry and artillery.  The military liked the basic design and stuck with it.

A Model 1938 (M1938) lensatic compass manufactured
by the Superior Magneto Company of New York
Superior Magneto appears to have been the prime supplier of this
compass design during WWII

However, wartime experience also highlighted some shortcomings in the M1938 design.  It was somewhat fragile.  While not a toy, the M1938 was lightly built – just two stamped aluminum cups fitted together to form the compass bowl and lid.  It had no mechanism to lift the compass card off of the the pivot needle when the compass was closed.  A lot of compasses were damaged when the the tip of the pivot needle gouged or cracked the pivot jewel through rough handling.  But perhaps the biggest shortcoming of the M1938 compass is that it had no dampening mechanism. This meant that the compass card would swing wildly and would take a good number of seconds to settle down to the point where the Soldier could get an accurate reading.  There were some versions of the M1938, those manufactured by the W. E. Gurley Company (a leading manufacturer of surveying instruments), that included a needle lift mechanism that with practice could be used to brake or slow the compass card oscillations.  However, the vast majority of compasses were manufactured by the Superior Magneto Corporation and did not include this needle lift mechanism.

After WWII the Army incorporated induction dampening into the M1938 design.  Induction dampening is a beautifully simple concept.  It takes advantage of the inductive magnetic field generated between a swinging compass needle and a highly conductive but non-magnetic alloy like copper.  When a magnetic needle (or bar) is placed inside a cup made of copper and the needle swings (oscillates) that movement causes a slight magnetic eddy current to form.  When the needle swings to the left the eddy current pulls it to the right.  When it swings to the right the eddy current pulls it to the left.  The eddy current is self-canceling; as the needle oscillations decrease the eddy current strength decreases and very quickly the needle settles down and is aligned with magnetic north.  Simple, elegant and effective.

A late model M1938 compass with induction dampening.  This is
a transitional design, bridging the gap between the original M1938 compass
and the the M1950.  The white colored compass bowl is actually
a copper cup that forms part of the induction dampening system.
This compass was made in December 1950 by the
Marine Compass Company out of Pembroke, Massachusetts.

However, by the late 1940s the Army decided it was time for a whole new design.  The Army took the best functional elements of the M1938 compass – the lensatic sighting design and the combined degree and mil scales on the compass card – added induction dampening, a needle lift device, a much larger sighting lens and a larger thumb loop and placed it all in a beefed-up waterproof aluminum housing.  The resulting compass was designated the M1950 Lensatic Compass.  It is a rugged, versatile device that has remained in use with the US military for over 60 years, pretty much as originally designed.

M1950 Lensatic Compass
This particular compass was manufactured in February1953 by the
Marine Compass Company out of Pembroke, Massachusetts.   The
cloudy dial cover is the result of the plastic aging.  Remember, this compass
is almost 60 years old!
Same compass with the cover closed, showing the manufacturer and
manufacturing date.

Fast forward almost 60 years and the same compass design is still in use by the US military, and it doesn’t look like they have plans to switch designs any time soon.

M1950 Lensatic Compass manufactured in 2010 by the Cammenga Corporation
out of Michigan.  This is a military issue compass that uses tritium inserts
for night time illumination.
The same compass with the cover closed.  At the time of this writing
Cammenga has been the sole supplier of lensatic compasses to
the US military for over 10 years.

Since 1950 this compass has been produced by a number of manufacturers, including the Marine Compass Company, Jay-Bee, Union Instrument, Cammenga and even Lionel (yes, the train people!).  However, it seems that the single biggest manufacturer of M1950 compasses was Stocker & Yale out of Massachusetts.  I don’t have any specific production numbers for these compass manufacturers so my claim is based solely on personal observation.  Based on the compasses I was issued in the Army and what I see for sale on auction sites or in surplus stores it appears that Stocker & Yale had the highest production numbers.

Now, the US military doesn’t just turn to a manufacturer and say “Make it!”  Like all things military there are clearly defined specifications.  It doesn’t matter if you are building an aircraft carrier or a handheld compass, there must be clearly spelled out specifications!  So it is with the M1950 Lensatic Compass.  Today’s compasses are built and tested in accordance with the DOD military performance specification known as MIL-PRF-10436N (Performance Specification, Compass, Magnetic, Unmounted, Lensatic, Luminous, 5 Degree and 20 Mil Graduations, With Carrying Case).

The document that spells out the design, construction,
performance and testing requirements for the
lensatic compass

(I should note here that the current specification does not use the ‘M1950’ designation.  I’m not sure when the US military dropped the designation, but for our purposes we’ll continue to call it the M1950.  It’s the same compass.)

The discussion of this performance document is important because the M1950 compass is the only US produced handheld compass I am aware of that is built to a specific performance specification, and is regularly evaluated against this performance specification by an outside agency.  If any test batch of compasses fails the evaluation the devices never make it out of the factory.  The M1950 is a purpose-built device designed to meet a clearly laid out specification not just for accuracy but for shock resistance, water resistance, illumination, thermal shock, durability and service life.  Manufacturers of other compasses may have their own internal standards (and many are quite good), but the M1950 is the only handheld compass you can buy that is designed to meet demanding military standards and is rigorously tested by an independent agency to ensure it meets those standards.

So just how good is the M1950 compass in the real world?  Pretty damned good!  The 58-year old example I show above that was made by the Marine Compass Co. is still perfectly serviceable and would probably meet all of today’s performance specifications for accuracy and durability.  I have other examples in my collection that have clearly seen hard use, some with broken components or cracked dials, but they still provide reliable and accurate readings. The M1950 compass is a device that is hard to kill.

I believe that the key to the M1950’s ruggedness is the fact that is it not a liquid dampened design.  Liquid dampening (where the compass needle or card is suspended in fluid to reduce oscillation) is very effective but is a more fragile design than the induction dampening used in the M1950.  With the liquid filled design the compass needle or card must be sealed inside a leak proof capsule*.  The problem is, compass manufacturers have not yet figured out how to make a leak proof capsule.  I have over 15 liquid filled compasses in my personal collection.  About half have air bubbles inside the capsule, a sure indicator that the fluid is leaking.

How accurate is the M1950 compass?  Every M1950 I’ve used (and after a 23 year Army career I’ve used a lot of them) has at least met, and many exceeded, the performance specification for accuracy.  Now this is where I need to come clean on my evaluation of the M1950.  It is not the most precise handheld compass available.  This compass’ biggest design limitation is that the compass card is divided into only 5 degree increments; pretty coarse even for handheld use.

Compass card of the M1950 compass.
Note the inner degree ring (in red) laid out in 5 degree increments.  The outer
ring (in black) is set out on mils (6400 mils to a circle).

This means that the average user, the common Soldier, can only discern and measure to half of that increment – 2.5 degrees.  Experienced users – mostly infantry and artillery Soldiers who use a compass regularly – can frequently get accurate readings to between 1.5 – 2.0 degrees. But to be realistic, 2.5 degrees is about as good as anyone can expect to get with this compass card layout.  The M1950 compass card design is a compromise.  The military needed to include a mils scale for use by the Field Artillery.  Mils offer more discreet division of the circle (a mil is 1/6400th of a circle), allowing for more precise azimuth determination – very important when you are calling in artillery strikes on distant targets.  To accommodate the mils scale it needed to be printed at the outer edge of the compass card, leaving less space to print the degrees scale.  This results in a coarse, less precise degree scale.

The military performance specification states that the compass must be accurate to within 40 mils.

“ Magnetic performance and compass error.  The compass shall be placed in a horizontal position on a fixed point and by means of the sighting mechanism, the compass shall be sighted on three targets of known magnetic azimuths approximately 120 degrees apart.  With no remedial action by the operator, before, at, or after, a reading shall be taken at each target.  The difference between the known azimuths and readings taken is the compass error.  An error greater than 40 mils or failure of the compass to function correctly shall constitute failure of this test.”

Since one degree = 17.8 mils, 40 mils is slightly less than 2.5 degrees.  Let’s round up and call it 2.5.

I have tested my 2010 production Cammenga compass at a known azimuth station and found it to be accurate to just over 2 degrees when used in the handheld mode and sighting on targets up to 150 feet away.  This compass very easily meets the performance specification.

Before I wrap up this blog post I need to add that the M1950 compass was merely one component of a land navigation system that the Army developed and adopted at the end of WWII.  Along with the M1950 compass came dramatic changes in how the Army mapped the world, developing standardized maps with overprinted grids (the Military Grid Reference System) and plotting tools.  It was all designed to simplify land navigation for the common Soldier, and is was so successful that the methodology is still in use today.

The US Army’s standardized land navigation ‘system’ included the M1950 compass,
standardized topographic maps, plotting tools and training materials.  It was an
extraordinarily successful program that is still used today.

Let’s wrap this up.  Here is my bottom line – I consider the the M1950 compass to be the best general purpose handheld compass available.  It is a proven design that is built and tested to exacting standards.  They are readily available new or used to civilians and are one of the best examples of trickle-down military technology I’ve seen.  If you spend any time in the outdoors you need a compass.  You might as well get the best available.  Get a M1950 Lensatic Compass.


– Brian

*One compass manufacturer, K&R out of Germany, claims to make a leak proof liquid capsule but I don’t think they have been on the market long enough to have proven the claim.