History: The US "optics crisis" in 1943

[GoodGuy]

The US "optics crisis" (1943)

The following quotes are excerpts authored by D.M. Mattox (In his book "The foundation of vacuum coating technology" (2003), Mattox - a B.S. degree in Physics from Eastern Kentucky State University and M.S. degree in Solid State Physics in 1960 from the University of Kentucky - describes some of the techniques used by the Germans), which demonstrate what had led to the German's advanced optics. Some of the corresponding German patents were granted around 1938/1939, declared to be military secrets right away and not published, where relevant developments and inventions/patents that lead to sophisticated coating/processing of lenses - used in cameras, gunsights, film projectors and other applications - are listed by Mattox:

ORIGINAL : "The foundation of vacuum coating technology" by D. M. Mattox , 2003
page 21 ff.

"In 1817 Fraunhofer noted that optical lenses improved with age due to the formation of a surface film. Following this discovery many investigators artifially aged lenses to form antireflection (AR) coatings. For example, in 1904 H. D. Taylor patented (British) an acid treatment of a glass surface in order to lower the index of refraction and the reflectivity by producing a porous surface. In 1933 A.H. Pfund vacuum-deposited the first single-layer (AR) coating (ZnS) while reporting on making beam-splitters [152] and Bauer mentioned AR coatings in his work on the properties of alkali halides [153]. In 1935, based on Bauer's observation, A. Smakula of the Zeiss Company developed and patented AR coatings on camera lenses [154].
The patent was immediately classified as a military secret and not revealed until 1940 (E-18).

In 1936 Strong reported depositing AR coatings on glass. In 1939 Cartwright and Turner deposited the first two-layer AR coatings. Monarch Cutler seems to be the first person to calculate the effect of multilayer coatings on optical properties. He did this as a Master's Degree thesis project. This work preceded the work of Cartwright and Turner, and, though unpublished, possibly inspired their efforts. One of the first major uses of coated lenses was on the projection lenses for the movie "Gone With the Wind", which opened in December 1939 (S. Peterson of Bausch & Lomb Optical Co.)[158].
The AR coated lenses gained importance in WWII for their light-gathering ability in such instruments as rangefinders and the Norden bombsights [159]."

During the African campaign the shortcomings of the US tanks' optics had alarmed US officials, so that - as a result - the US put quite some effort into overcoming what I would call the "optics-crisis" of 1943. Later in the war, Sherman tank optics were somewhat better (as magnification levels increased), but still did not match the quality of most (if not all) of the German optics.

"During WWII, baking of MgF2 films to increase their durability was developed by D.A. Lyon of the U.S. Naval Gun Factory [160]. The baking step required that the lens makers coat the lens elements prior to assembly into compound lenses. In 1943 (Oct.) the U.S. Army (The Optical Instrument Committee, Frankfort Arsenal) sponsored a conference on "Application of Metallic Fluoride Reflection Reducing Films to Optical Elements".

"The conference had about 132 attendees. The proceedings of this conference (112 pages) is probably the first extensive publication on coating optical elements. [161]. O.S. Heavens published his classic work, "Optical Properties of Thin Solid Films" (Butterworth Scientific Publications), in 1955."

The US Army obviously knew that at least proper coating appeared to be vital for getting improved optics, thus they sponsored the conference. Pre-processing the lenses (which the Germans did it seems) may have been vital too, but I don't know if that had been part of the Committee's evaluation, too. The question is what the particular findings of this conference were, and when (and how) that showed on actual production models of tank optics. Afaik, even until 1944/45, US tank optics remained inferior, despite the introduction of optics with way higher magnifications (5x). The Russians, in turn, tried to copy the German optics, and at least the ones employed in IS-2 tanks were really good (astounding max range).

"The Germans deposited CaF2 (calcium fluoride) and MgF2 AR coatings during WWII [162]. Plasma cleaning of glass surfaces is reported to been used by Bauer at the Zeiss Company in 1934 [162]. The Schott Company (Germany) was also reported to have THREE-LAYER AR coatings by flame-pyrolosyis CVD during WWII [162].
Vacuum evaporation of metals (Cd and Zn) on paper web for paper-foil capacitors was begun in about 1935 by R. Bosch of the Bosch Company of Germany, who discovered that there was a "self-healing" effect when there was an arc between the low-melting-point thin film electrode materials [163]. By 1937 the Germans had demonstrated that the use of a "nucleating layer" increased adhesion of zinc to a paper surface [164]. The effect of nucleating on film formation had been noted by Langmuir as early as 1917 [165].

In 1958 the U.S. military formally approved the use of "vacuum cadmium plating" (VacCad) for application as corrosion protection on high-strength steel to avoid hydrogen embrittlement associated with electroplated cadmium [166]. In recent years PVC processing has been used to replace electroplating in a number of applications to avoid the water pollution associated with electroplating."

Even though it looks like the author, who is obviously a scientist/engineer, he seems to have randomly collected and listed coating attempts, patents and innovations, and he actually outlines - almost in shorthand format - what processes were known in the western world, and what other processes - which either just remotely dealt with coating or which could have also led to a proper knowledge level in the optics field - were known.

I am not a physicist, nor a chemist or photographer/photography engineer, but as I understand it, the coatings provide for more clarity by allowing more rays of light to pass through a lense (or set of lenses, which you need for higher magnification levels), by applying such anti-reflection coating:

• Basically, without coating, the more lenses (that had been produced in the old fashioned way) the Allies put into a telescope (to receive a higher magnification), the more clarity got lost (10% with each lense). I've read that a 40% loss of clarity definetly impacts usability, so a US 4-lenses-system wouldn't have been too helpful for a tank gunner. The Germans, in turn, were using 4-lenses in their systems without any problems.

• Also: the more lenses the more restricted the field of view (12° FOV for many US gun optics only, while German optics had 25°). So, generally, German tanks in Africa had partially inferior (Pz.III?) magnification, the same (PzIV?) or even better magnification (Tiger?), but absolutely superior clarity, and twice the field of view compared to Allied systems.

• After the Western Allies had upped their magnification levels to 4x and 5x (1943?), the Germans followed with the introduction of 4x and/or 5x (Panther) magnifications, at some point, which then offered even more superior optics, as their 4-lenses-systems (for example) only lost 16% of clarity, instead of 40% (on the Western Allied systems).

Zeiss used a special technique developed in 1938 which involved an AR coating on the lenses, reducing the loss (of clarity) per lense to 3-4%, which allowed for the production of sighting systems with 4 lenses and more, while maintaining the clarity of a Western Allied gunsight that carried 1 or 2 lenses only. The Western Allies didn't know about that production method until after the war (I am not sure about the Russians).

The footnotes in Mattox' work:

"(E-18): After WWII the japanese camera makers (Canon and Nikon) infringed on many German camera patents. When the Germans complained, the Allied Control Commission for both Germany and Japan took no action. This allowed the Japanese to rapidly build up their camera industry to the dismay of the Germans. (Information from "Post War Camera & Lens Design Thievery" by Marc James Small). As far as the author can tell the Japanese did not use coated optics during WWII."

Some German historians suspect that the Japanese military got all infos regarding coating and lense technologies, along with blueprints of military applications and weapons shortly before Germany was forced out of the war. Some tech-transfer attempts (like a disassembled Me 262 + blueprints aboard a submarine, which surrendered on the Atlantic Ocean - after is had received the radio message that Germany had surrendered, leading to the 2 japanese officers - ordered to escort the precious cargo - committing suicide aboard) either did not make it to Japan, or took several attempts (even with rumors about an alledged long-range flight of the only (and famed) German long-range bomber using the route over Syberia). Whatsoever, the Japanese became the leaders in the camera sector by using the German technologies as foundation, most likely, as Canon and Nikon did not even attempt to acquire the camera (and lense) patents, since they must have had all the infos about the manufacturing process, already.
Mattox seems to think that the optics technology was passed, but I can't remember whether he mentioned it explicitly, or not. (I'd have to dig for his thesis). If not, he must have omitted his personal thoughts, as there is no particular evidence to prove that particular transfer, yet.

 

[Bullman]

Thanks for posting. Very intriguing piece of history.

 

[GoodGuy]

Thanks for posting. Very intriguing piece of history.

You're welcome. The post above is a compressed version of various posts I created like 6 years ago, when the Russian (?) TOW2 developers didn't want to believe that German optics were more advanced than most of the Allied systems, and that only Russian engineers managed to catch up with the German technology (to some extent, and rather late in the war - IS-2 had decent optics and an amazing max. view range [I do not have exact data here], for sure, 2 or 3 very late Russian TDs/assault guns [1944/45] may have received similar optics). So, there were some more details, but this is basically the essence of what I researched back then.

 

[GoodGuy]

I found the rest of my old posts, check it out:

ORIGINAL: G. Green, in "Panzers At War", page 60

"German optical sights were far superior to anything the Western Allies or the Red Army mounted on their tanks during World War II.Tom Sator, an M4 Sherman medium tank crewman who served in the U.S. Army's 4th Armored Division in Western Europe from late 1944 through the end of the war, remembers his first chance to look through the gunner's sight on a Pz.Kpfw.IV with the long 75mm gun tube:

'There was always a lot of talk about the effectiveness of the German tank guns against us. It is true that they had to stop to fire, but they started firing from 1,200 to 1,500 yards (1,096 to 1,371 meters). Their first shot was always a hit. We, on the other hand, had to get within 500 to 600 yards (457 to 548 meters) to be within effective firing distance, and even our best gunners needed at least two shots before they could score a hit.
Our CO (commanding officer), Captain Jimmy Leach, sent the platoon sergeant down to my tank during one of the lulls between German artillery barrages, and he hollered up, 'Hey Sator, you speak German?' 'Yeah, why?' I answered. 'The radio in that abandoned German tank (Pz.Kpfw.IV) back there is alive. Captain wants you to listen and see what they are talking about'. So, I went with him. Sure enough, when we got there, you could hear the radio squawking. I climbed in and put the gunner's earphones on. It was difficult to hear, and because the guy was talking in a strange dialect, I could understand only a few words here and there. Then I saw the gun-sight and I figured I might as well look through it while I was there, and as soon as I did, almost immediately, the realization came to me why the German tank gunners were so accurate. 'Shyte, I wanna go home' is the only thing I could think of at the moment. Their sights were so far superior to ours that we didn't stand a chance.' [Tom Sator] "

The US periscope systems were still interesting:
While US gun scopes (fixed + aligned with the guns) had really limited view ranges (from ~8° - 12°, later on 18° and even 21°), most US tanks/gunners had a somewhat adjustable secondary sight, which offered up to 42° 10' (horizontal) FOV (eg. the M10 system, see below), an amazing and really high value. I'm not that familiar with the " X° Y' (minutes?) values, but it should mean that it's not much over 42 degrees, if I am not mistaken.
The downside of this superior battlefield view was that these scopes usually had 1 x magnification only and a really restricting vertical FOV of only 8°11' .

As we know (now), the 5x and then finally this 6x magnification in the M10 periscope was the US attempt to make up for the very blurry images at medium and long ranges. US tank scopes had some kind of coating (a corresponding label/sign can be seen on many pictures of M4A1 scopes which are still frquently traded on ebay and the like - note: the model designation does not stand for the tank using the scope, but it was an independent label/model description, which even confuses collectors .... so, in fact, that particular scope went in all kind of light and medium tanks and even TDs, see the PDF above). But since the coating was not as sophisticated as the German coating/processing, the gunners received a better magnification level, but either the same amount of blur, or even more blur, when another lense was added to achieve a higher level of magnification, and the 1-power scope could not help to identify whereabouts of foes at medium and long ranges.

Roman Jarymowycz, in his book "Tank Tactics: From Normandy to Lorraine" (ch. 13), gives a good account of the German advantage:

ORIGINAL: Wikipedia (yeah i know, but i am too lazy to type it all myself, here ) excerpt summarizing Jarymowycz's statements covering this advantage:

Their gun sights were fixed magnification, while German tanks had multiple magnification settings. Sherman gunners did have the use of a secondary sight which allowed them a larger field of view over their German counterparts. However this advantage was mostly useful in close range situations [only], due to lack of magnification. In summer 1944, after breaking out of the bocage and moving into open country, U.S. tank units which engaged at longer ranges from German defensive positions sometimes took 50% casualties before spotting where the fire was coming from.

Another quote, from "M4 (76mm) Sherman Medium Tank 1943 - 65" by Steven J. Zaloga, page 6, discussing the shortcomings of the earlier versions of the M4 (with the 75mm gun), particularly the periscopic gun sights in the early versions (M38A2 ?):

"The fighting in North Africa revealed the inadequacy of periscopic sights for gun aiming, and both US and British officers recommended following the German example and shifting to a high-power telescopic sight. As a result, the M1 gun was mounted on the modified M34A1 combination gun mount with a new telescopic sight."

The M70 series telescopes, which probably didn't make it in numbers to the African theater (if at all), were 3-power scopes, they offered 12° FOV, they were usually only mounted on 76-mm Shermans and they were only mounted on "older" Shermans (if possible at all) when they hit the shops/factories for repairs (or gun/turret upgrades?), but even the Chief of Ordnance, in his brochure from 1st of October 1944, so in late 1944, stressed that scopes of the M50 series still in use would be replaced in a gradual process, only:

http://www.simcentrum.com/uploads/USTank-optics.pdf

ORIGINAL: Office Chief of Ordnance 1 October 1944
in an info brochure about US periscopes:

"TELESCOPES, M51, M54, M55, M56A1 -In appearance, these telescopes resemble those of the M70 series. They contain the Armored Force Reticle instead of the recently adopted antitank reticle. Telescopes, M51, M55, and M56A1, are identical with the M70 type except in the type of reticle and optical glass. Telescope, M54, possesses slightly different optical characteristics. All these telescopes are to be replaced by M70 type instruments whenever they are turned over to Ordnance personnel for adjustment."

I am not familiar with those particular scopes and what magnification levels their scopes featured (1.8x ? 3x ?).

The M71D scopes offered 5x magnification, and their reticles were graduated for 76-mm AP rounds.

Many of the high-power scopes were prioritized for tank destroyers, as the 75-mm and 76-mm Sherman's roles had shifted more and more towards infantry support, in late 1944, because their guns had become too inferior.

The M10 periscope was then the most sophisticated periscope, as it combined 2 telescopes in one body, and as it featured a 6x-system and a 1x-system:

ORIGINAL: Office Chief of Ordnance 1 October 1944,
in an info brochure about the M10 periscope:

"This periscope is constructed on principles entirely different from those previously considered, for it is really two self-contained telescopes in one body which is linked with the gun.There is a 1-power optical system which is used for firing at near targets and a 6- power system for firing at distant or indistinct targets. The 6-power telescope has a true field of view of 11° 20’, a 7 mm- exit pupil, and eye relief of 29 mm. The 1-power instrument has a vertical field of view of 8” 10’, a horizontal field of view of 42° 10’, and unrestricted eye relief. The 1-power telescope has an infinity reticle and the B-power instrument has the standard antitank type reticle, graduated for use with the tank gun."

EDIT:
I wasn't sure about the term "substitute standard" (page 324 A), but I am convinced now, that the term meant that all periscopes that were "turned over to Ordnance personnel for adjustment" were then to be replaced by the M4A1 periscope, which was used with the following telescopes:

Used with: ..................... Used in:
Telescope M38A2 ........ Medium Tanks, M4 series - Gun sighting and observation
Telescope M40A2 ........ Light Tanks, M3A1, M3A3, M5, M5A1
Telescope M47A2 ........ 76 mm Gun Motor Carriage, T70; M18; Medium Tank M4 series (76 mm) - Gun sighting and observation

All of these telescopes were 1.44-power-scopes only, and had only 9° FOV, so I am wondering whether these actually just served as observation devices, or actually as gunsights, as the M70 series were 3-power telescopic sights and introduced in 1943, and 1.44x seems really low for a gunner's scope and low for being declared as substitute standard.
The US model numbering is quite confusing, at least.

While it looks like the self-contained M10 (periscope+telescope) were earmarked to be the future solution for the M4 series medium tanks, I do not know if or when M10-scopes were mounted during the war in the European theater.