Monday 2 May 2022

The Fight for Sight

Optics often come up in discussions that compare Soviet and German tanks. The famous "Zeiss optics" are often invoked by those who are not very well versed in the subject matter. The issue was not in Soviet sights. Plenty of them survived to this day, and any who wish can evaluate their quality on their own. German tanks were first and foremost superior in their observation devics. Their visibility was better than that of Soviet tanks, which was often a deciding factor in victory on the battlefield. However, the evolution of German observation devices is an interesting topic for discussion.

Pre-war evolution and lessons from Spain

The Germans did not have an advantage in observation devices right off the bat. The observation devices and sights used on German tanks after 1933 were the result of a long evolution that is often forgotten. Successful designs are often reached via trial and error. The Germans were not an exception here. Work on observation devices began during the First World War. The commander's cupola as we know it appeared back in 1918 on the Sturmpanzerwagen Oberschlesien that remained on paper and LK-II that was built in metal after all and is better known as the Strv m/21.

A variant of this tank with a turret and a machine gun was built during WWI, but there was no time to finish it. Joseph Vollmer's design that didn't quite make it to the battlefields of WWI had quite good visibility for its time. It had a commander's cupola with observation slits and observation devices in the turret, some of which could be closed with armoured shutters. Compared to this tank, the Renault FT looked like a cramped and blind tin can. Swedish tankers who tested a Renault FT said the same thing. It had a commander's cupola, but you couldn't see much from it. The LK-II still suffered from the typical issues of tanks of that era, namely that the observation slits weren't protected and fire aimed at them could harm the crew.

The LK-II had a commander's cupola and vision slits, some of which could be covered with shutters. After the end of WWI these ideas were lost.

The Germans did not make use of their experience from WWI. The sights and observation devices that were designed starting in 1926 had nothing to do with Vollmer's work. Krupp and Rheinmetall went their own way when they developed turrets for their new tanks, and this was sometimes nonsensical. The Armeewagen 20 (later renamed Grosstraktor) had its commander removed from the turret and placed in the hull to the right of the driver. He had an observation cupola that let him see something, but not much. The two-man turrets had two periscopes (one of which was the sight) and a pistol port for the gunner. That's it. The Germans tactfully avoid mentioning the vision from this tank, which was quite poor.

The Leichttraktor turret was even stranger. It was developed at Rheinmetall. It seemed more rational than the Grosstraktor's turret. It had the same pair of periscopes plus vision slits covered with armoured glass in the side hatches. However, this was not a two man turret. It initially contained three crewmen: the gunner sat on the left, the loader on the right, and the commander in the back. He was the one who would use the observation periscope. The first trials at TEKO showed that this idea was absurd. It was way too cramped inside the turret, so the commander was moved out of there and only two men remained.

Periscopic sights were common for pre-war German tanks.

The vision of the first German tanks was quite poor and definitely no better than any foreign analogue. Nevertheless, the idea with an observation periscope and a periscopic sight was used by other nations. The USSR copied it from the Germans to create the PT-1 panoramic sight and PTK commander's periscope. The Leichttraktor turret also migrated to the Swedish Strv m/31 tank. Later Swedish tanks had the same design, especially when it came to the sights and observation devices. The Strv m/38 had a commander's cupola and a slightly different turret. Through Sweden (specifically, Bofors) the idea made its way to Poland, making the Leichttraktor and 7TP distant relatives. The gun mount and sights have common roots.

Sweden picked up German pre-war tank design ideas. The Strv m/31 and other tanks that were built there show signs of German influence.

Work on a new medium tank initially called M.Tr. began in July of 1932. This work was given to Rheinmetall as the developers of the most successful Grosstraktor variant. However, this was a whole new tank with very interesting features. It would appear that the Germans carefully looked at the British Medium Tank A6, since some ideas were clearly taken from there. The machine gun turrets had two machine guns each, just like the British ones. The main turret was also similar. The biggest novel feature was the commander's cupola. It was moved to the back of the turret and housed in a bulge. Development of the M.Tr. tank led to the Nb.Fz. This tank was a dead end but hosted a large number of technical solutions that later became foundational for German medium and heavy tanks. This was also true for the observation devices. The commander had a cupola in the back of the turret, behind the gun. The machine gun turrets also evolved into the turret of the La.S. light tank, better known as the Pz.Kpfw.I. This turret was the first in a long line of horseshoe shaped turrets that the German tank designers were so fond of.

Initial draft of the Nb.Fz. tank. This was a pivotal vehicle for German tank building, as many observation solutions migrated from this tank to other German tanks.

There were some nuances of the Pz.Kpfw.I turret when it came to optics. The tank had a 2.5x T.Zf.2 telescopic sight. The Germans did not follow the established practice of just using a tube with lenses on the end and developed a complex sight with a bend in it. This placed the sight opening above the gunner's head, making aiming safer and making it easier to place the sight. The Pz.Kpfw.I turret developed by Daimler-Benz was the first to receive observation ports in the gun mantlet. This was a controversial decision since it could result in a bullet to the commander's face, but the same solution migrated to the Pz.Kpfw.II and Pz.Kpfw.III. The Pz.Kpfw.IV turret developed by Krupp also had forward facing vision ports, but they were in the front of the turret and not the gun mantlet. There were also four more observation ports on this turret on the sides and rear.

The Germans settled on the horseshoe shape for their tank turrets starting with the Pz.Kpfw.I. This tank also heralded a new era for tank observation devices.

Observation improved as a result, but some of these decisions were not without drawbacks. Only the rear two observation ports had vision slits. To see something through the other ones, you had to open them and risked catching a bullet. The ports with vision slits had tempered glass vision blocks analogous to those developed by Sekurit. This was a good idea, if only in theory. Analogous observation ports were placed in the turret platform.

The Pz.Kpfw.II tank had a combat driving vision device, a typical feature of German tanks.

Evolution of observation devices continued on the Pz.Kpfw.II. The driver received a new observation device with a backup combat driving binocular vision device. It slid on rails along the roof of the driver's compartment. In battle, the vision port could be shut and the driver would observe through the device. This device was superior to the Pz.Kpfw.I driver's observation device and was also used on the experimental B.W. tank as well as the Pz.Kpfw.III Ausf.A. The new German medium tanks used a different sight. The T.ZF.5 was a so called refracting sight, meaning that it had a block of prisms that allowed the front part to be movable. This meant that the sight didn't have to sit right at the center of the turret and could be positioned anywhere that was comfortable for the gunner. This improved the gunner's comfort and therefore the precision of fire.

Improved observation devices that appeared as a result of studying experience from Spain.

Combat experience in Spain followed. The Germans offered the Condor Legion armed with Pz.Kpfw.I Ausf.A tanks to Franco's forces. It quickly turned out that there was little that German machine guns could do with Soviet T-26 tanks. One German tank was captured and studied at the NIBT Proving Grounds. The Soviets had no complaints about the optics, including the observation devices. Meanwhile the Germans had a different opinion. Lieutenant Colonel von Thoma, the head of the group of German instructors and mechanics, composed a very critical report, which included the observation devices. It turned out that the vision slits were a good target for small arms fire, and the tempered glass is easily penetrated by bullets and shell splinters. It's worth noting that Soviet tempered glass offered better protection, even though the German devices had a wider range of vision. As a result, the Pz.Kpfw.II Ausf.A had better observation devices. The glass blocks were now 50 mm thick. The shape of the observation ports changed. The driver's vision slit changed most of all. It now had a V shape with a vision slit at the tip. The same slits were used on the Pz.Kpfw.IV Ausf.A and Pz.Kpfw.III Ausf.B-D.

Driver and commander's vision ports on German medium tanks in 1939 looked like this. These were some of the best vision devices at the time, but it turned out that using glass blocks was not the best idea.

The issue with protection for observation devices also had to be corrected on the commander's cupola. The existing design with no protection for its vision slits was vulnerable to small arms fire. However, the Pz.Kpfw.IV Ausf.A and Pz.Kpfw.III Ausf.A and B still had the old vulnerable design. Starting with the Pz.Kpfw.III Ausf.C and Pz.Kpfw.IV Ausf.B the tanks had a new cupola with a special shutter to protect the vision slits. This cupola design lasted for a very long time. The Pz.Kpfw.IV Ausf.B also received a new driver's vision device, the Fahrersehklappe 30. It had two shutters that slid up and down, offering more reliable protection. This device was also used on the Pz.Kpfw.II Ausf.E and used until mid-1940. It later appeared on the Pz.Kpfw.II Ausf.F. This device was designed to protect the driver from high caliber machine guns. New Sehrklappe vision ports were also introduced. These were larger and had thicker glass blocks. 

By the start of the Second World War the Germans walked a long path developing their tank optics. By that point they were the clear leaders in observation device design. There were certain drawbacks, but those will be discussed later.

Falling behind

The Polish Campaign revealed some issues with German observation devices. The medium tanks were more or less okay, at the very least there were no obvious issues, but evidence still pointed to deeper problems. The Fahrersehrklappe 30 didn't fully protect the driver from shell splinters or bullets larger than rifle caliber. The system with lifting shutters took up too much space and could jam. A new variant of the Fahrersehrklappe 30 was introduced in the spring of 1940 as a result. There was only one shutter instead of two that reliably covered up the observation slit. A new commander's cupola was also developed. Its shutter was split into fragments that could be raised and lowered individually.

Medium tank observation devices were improved as a result of the Polish campaign. Further improvements were limited to thickening their armour.

The situation with the Pz.Kpfw.II, Germany's most numerous front line tank, was more difficult. The idea with lots of observation ports may have worked well in peacetime, but in wartime German tankers cursed the tank for its poor vision from the commander's seat. Meanwhile, the Germans got their hands on the most progressive invention of the Polish defense industry: the Gundlach periscope. Periscopic observation devices existed before, for instance Czechoslovakian tanks had periscopes in their commander's cupolas, but their designs were complex. Gundlach's periscope used a system of prisms, which was much simpler and more reliable than mirrors. In case the periscope head was shattered, it could be removed from the inside and put back into action with a spare prism. The periscope could also turn and tilt. This was an excellent periscope and variants of it are used in armoured vehicles to this day.

The Pz.Kpfw.II's commander's cupola was the first instance of prism periscopes being used on German tanks.

The Germans regarded Gundlach's invention highly, but copied it in their own special way. It seems that they missed the genius of making the periscope rotate. Work to begin installing commander's cupolas on Pz.Kpfw.II tanks began in October of 1940. It had eight periscopes similar to Gundlach's design. The result was quite successful, perhaps the best commander's cupola of its time. The all-round vision was very good and the periscopes were covered up from the top. The cupola was very low and the commander's head was still inside the turret, a good decision when it came to safety.

The Germans copied the Gundlach periscope, but only in part.

The British were also using Gundlach periscopes by this time, and the USSR was using its own mirror periscopes, primarily on the KV tank, although the devices were inferior in construction and placement. It had a lot of periscopes, but they were places poorly and so the vision they offered was not good. This is why trials of the Pz.Kpfw.III Ausf.G tank purchased in 1940 had such a great impression. Even though this tank still had old observation devices, they offered good vision. As a result, the KV-3 was going to have German-style vision ports in the side and a commander's cupola. Unlike the Germans, Soviet designers put periscopes instead of glass blocks in their cupola from the start. 

An example of German conservatism. The Tiger (P) had no periscopes at all.

Seeing prismatic observation devices usually meant that nations would switch to using them, but not always. Strangely enough, sometimes these devices were at least partially discarded. This happened with German heavy tanks. The VK 30.01 (H) was supposed to have a whole battery of periscopes: one for the gunner, two for the loader, and the commander had a Pz.Kpfw.II style cupola. However, the gunner and loader's periscopes were fixed, which severely limited their vision. The VK 36.01 turret was similar, but the gunner lost his periscope. Both turrets had observation ports in the side.

Compared to this, the turret of the VK 30.01 (P) that later evolved into the turret of the Tiger was a step backwards. It had no periscopes at all, just outdated vision slits with glass blocks. This was a strange decision for a heavy tank that was supposed to have thick armour. It was clear that infantry would prioritize these targets. The driver's vision devices were just as odd. The VK 30.01 (H) had the Fahrersehklappe 50 (essentially the Fahrersehklappe 30 but for a 50 mm thick plate), while the VK 30.01 (P) and VK 36.01 had less progressive designs. The vision block was bulkier and returned to the lifting shutter that was more vulnerable to enemy fire.

Observation devices in the Tiger Ausf.E.

The situation with the Tiger Ausf.E's observation devices was odd to say the least. It combined the progressive T.ZF.9b binocular sight and outdated vision devices. The turret had no periscopes at all to start. The gunner and loader only had vision slits in the side to look out of. There were periscopes in the hull, in the flaps of the driver and radio operator's hatches. Someone up high must have considered rotating periscopes against ordnung, and so they were fixed in place meaning that you could see precious little through them.

Observation ports were priority targets for infantry.

The commander's cupola was quite tall, which made it a tempting target for enemy gunners (for instance, it was indicated as such in Soviet instruction manuals). Otto Carius' memoirs show what German tankers thought about the Tiger's cupola.
"The entire commander's cupola had flown off my "Tiger". I had shrapnel in my temple and face. The wounds bled profusely, of course, but nothing had happened otherwise. The entire affair could have turned out considerably worse. Kramer had always chastised my smoking. But he had been taught a lesson; if I hadn't bent over to light up my cigarette, then my head would have been in the cupola at the critical moment. It hardly needs to be mentioned that I would have "lost my head" in the truest sense of the word.

I wouldn't have been the first one that had happened to. The reason could be found in a design failure. On the initial "Tigers" the cupola was still welded. It rose up high and had direct vision slits. The cupola hatch stood up vertically when it was opened. Thus, from a distance, anyone could recognize that the tank was vulnerable from the top. 

A high explosive round only had to hit the hatch and the entire charge then came down on the commander's head. If a commander wanted to close the opened hatch, he had to lean over on the outside of the vehicle and expose himself to the hip to unhitch a safety latch that released it."

Another thing mentioned in Carius' memoirs is often counted as a positive. German commanders often fought looking out of their turrets. Carius considered this an advantage over Soviet tanks. This fact brings up an interesting consequence: the vision of German tanks was still insufficient. A head sticking out of a turret was a priority target in battle. Carius admitted this himself and later acquired a binocular periscope to look through. 

The Panther was in a similar boat when it came to observation devices.

The next German tank, The Panther, had all the same drawbacks. It had a similar cupola with vision slits covered by glass blocks. The gunner and loader had no vision slits, let alone periscopes. This was a strange solution to pair with the high tech T.ZF.12 binocular telescope sight. The vision situation in the driver's compartment was slightly better. The driver and radio operator/hull gunner had periscopes. The driver also had a vision port in the upper front plate. This port was used during driving since it offered much better vision. However, not one of these periscopes could rotate, which reduced their usefulness. This also meant that little by little, German tank designers made their tanks blind on the flanks.

The Tiger and panther later received new commander's cupolas, but they were still very tall and vulnerable.

This can be seen through the evolution (or rather degradation) of observation devices in German medium tanks in 1942-1944. The changes began in 1942 due to a large number of anti-tank rifles coming into service with the Red Army. Anyone who thinks that the leaflets pointing out the location of vision slits on German tanks were only good as toilet paper is sorely mistaken. Blinding enemy tanks was a high priority task for Soviet infantry, and one it performed well. As a result, German tanks lost their vision ports on the side. They didn't have vision slits anyway and weakened the turret armour. The Pz.Kpfw.IV Ausf.G also lost the loader's vision port in the front. Observation ports in the turret platform sides were the next to go. Finally, the only vision devices remaining were the commander's cupola, gun sight, and his vision port (although it was removed on the Pz.Kpfw.IV Ausf.J), as well as the driver's observation device. The combat driving device was removed on the Pz.Kpfw.IV Ausf.H.

The situation with observation devices on the Pz.Kpfw.IV by 1944 was dire. There was no way to look sideways aside from the commander's cupola. The vision ports in the turret hatches were covered by spaced armour.

The Germans were not alone in this. Since all infantry loved to shoot at vision ports, they disappeared from American tanks as well. However, there was a big difference. Other nations replaced vision ports with periscopes that were either a direct copy of the Gundlach periscope or were built according to similar principles. For example, the USSR introduced the MK-IV periscope in 1943. The Germans on the other hand removed observation devices without replacing them with anything, even though there was a possibility of putting a periscope on the Pz.Kpfw.IV turret. Paradoxically, in 1944 German tanks suffered from the same issues that Soviet ones did in 1941-42.

German tanks were extra vulnerable from the flanks by the end of the war, the same thing that happened to Soviet tanks in 1941-42.

Of course, the Germans did work to correct their mistakes. The Tiger Ausf.E received a loader's periscope and a new cupola with prismatic observation devices. The Panther went through a similar evolution, also losing the vulnerable driver's vision port. These were all half-measures. The Tiger Ausf.B tank that made its debut in 1944 had the same problem with sideways vision. What kept German designers from putting rotating periscopes on their tanks remains a mystery. They could have used the same periscopes as on the Ferdinand (which had a whopping three periscopes, a record for the Germans), but didn't for some reason. It's very strange to observe a lack of these periscopes on tanks when they were also used on the Jagdpanzer IV and Jagdpanther

The Germans were capable of making rotating periscopes, but didn't put them on tanks.

The situation with tank production in 1944 had its effect on tanks. The German "beasts" had to transition to monocular periscopic sights. However, it's not hard to notice that the crisis began long before the situation became difficult. Other nations had their own issues, but the overall picture is clear: while everyone else's tanks got better vision, the Germans only got worse.

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