African Pz.Kpfw.III

The heavy Panthers and Tigers are the best known of Germany's tanks. The lion's share of discussions of armoured vehicles in the Second World War is dedicated to them, even though lighter tanks carried the Panzerwaffe through the majority of the war. The Pz.Kpfw.III tank proved itself to be a worthy opponent in the first half of the war. At the same time, it remained a mystery for the British for a number of years until the first trophies began arriving from North Africa in 1941-42. This is what the British learned from these studies.

Third time's the charm

The Pz.Kpfw.III medium tank was posed as Germany's main tank from the early days of the Nazis' reign, but development was slow. Only 120 tanks were in the field by the start of the Second World War and 381 by the beginning of the Battle of France. Serious losses among them prove that they were actively used and the British Expeditionary Force couldn't have avoided meeting them on the battlefield. However, even if a tank of this type was captured there was no opportunity to study it or send it back to Britain. The speed of the German offensive forced the British to abandon even their own tanks on the continent.

A column of Pz.Kpfw.III tanks in France prepares to move out. The British did not gather any detailed information on these vehicles in 1940.

Second Fiddle

Even though the German Pz.Kpfw.IV tank was originally created as a support vehicle (Begleitwagen) and fell short of its counterpart the Pz.Kpfw.III in many ways, it was still the heaviest tank in the German arsenal and mounted the largest caliber gun. Issues with Pz.Kpfw.III production also made it the most numerous German medium tank at the start of WWII. Despite its “secondary” designation, the Pz.Kpfw.IV did not evade the attention of the British. Intelligence agents and tankers alike strived to uncover its secrets.

A meeting in Africa

As with the Pz.Kpfw.III, the British only knew about the Pz.Kpfw.IV from rumours. There was little verified information, but one of the few things known for sure was that the tank was heavier than the Pz.Kpfw.III. Intelligence summaries referred to it as a medium tank, whereas the Pz.Kpfw.III was called a “medium-light tank”. Naturally, the British encountered the Pz.Kpfw.IV in France in 1940, but a sample could not be obtained for study due to the rapid defeat of the British Expeditionary Force. Even though there was no precise data about the armour or armament of the tank, an identification poster was still composed and distributed on December 16th, 1940.

A drawing of the Pz.Kpfw.IV Ausf.C composed according to intelligence data showing distinguishing features of the vehicle. The antenna deflector, fixed gun mantlet, pistol port in the single piece front plate, and driver’s observation slit were among the features unique to this variant of the tank.

Widespread Welding

"Order of the People's Commissar of Tank Production of the USSR #200s
Moscow
March 28th, 1943

The meeting gathered in response to my order given on December 18th, 1942 in Nizniy Tagil at factory #183 on the issue of widespread introduction of automatic welding explored the issues raised and came to the following conclusions regarding automatic welding.

Automatic Welding

"Order of the People's Commissar of Tank Production of the USSR #837s

Moscow

December 19th, 1942

Production using automatic welding under a layer of flux when producing armoured hulls at factory #183, UZTM, etc. proved itself as having several advantages over manual arc welding.

In addition to increased productivity, reduced electricity consumption, and the ability to use untrained workers, the high quality of the seams was proven. During proving grounds trials, they showed better resistance than welds made by hand.

Small Modernization of a Large Tank

Many tanks received significant upgrades after they first saw battle. Practice often trumps theory, especially during WWII where military vehicles quickly became obsolete. The IS-2 heavy tank was no exception. It was built with enough armour to protect it from the German Tiger tank, but it turned out that there were more dangerous opponents on the battlefield. As a result, a modernized IS-2 tank entered production in Chelyabinsk in late summer of 1944. It is sometimes called IS-2M or IS-2 model 1944, but neither designation was used in reality.

T-44 Under Fire

The T-44 proved a tough nut to crack. Neither the Soviet 85 mm gun nor the German 8.8 cm Pak 43 could penetrate the upper front plate even from 100 meters. The lower front plate could not be penetrated by the 85 mm gun either, but the 88 mm gun managed to break it off after several hits. Despite the welding giving out, the protection was much better than that of the T-34-85, comparable to the Panther.

"Firing trials against the armoured hull resulted the complete destruction of the following welding seams: 

• Upper front plate and left side
• Lower front plate and left side
• Idler carrier and sides
• Hull roof and left side

The welding seam between the hull roof and right side was destroyed by 80%.

The overall view of the hull from the front after trials is show in figure 21.

Photo 21. Overall view of the hull from the front after trials.

CAMD RF 38-11355-2909 p.31

Financial Gratitude

One of the biggest issues with T-34 production was the use of new austenitic electrodes, which welders were not skilled at working with. A group of instructors from the NII-48 research institute had to be dispatched to teach them how to work this this new type of welding, which radically reduced the amount of defective armour components.

"March 19th, 1941

#145189s

To the Chief of the 3rd Department of the NKSP, comrade Yushin

Director of NII-48, comrade A.S. Zayalov

Workers from the 3rd department of the NII-48 resolved a series of issues, which radically increased the quality of armour (austenitic electrodes, repair of armour, welding of thick armour, assistance to factories) by travelling to Podolsk factory and factory #183 to assist in mastering welding of armoured pats.

NII-48 Experiments, 1946

"Include the following topics in the research work for 1946:

1. Production tanks and SPGs:
1. Develop armour types for:
1. Light and medium tanks and SPGs, capable of resisting 75 and 88 mm guns with the muzzle velocity of 1000 m/s.
2. For heavy tanks and SPGs, capable of resisting 88 mm guns with the muzzle velocity of 1000 m/s and 122 mm guns with the muzzle velocity of 800 m/s.
2. Improve the hull and turret of the IS-3 tank:
1. Hull:
1. Improve the connection between mudflaps and tank side.
2. Increase the robustness of the rear of the hull.
3. Increase the perpendicular robustness of the hull.
4. Increase hull floor strength.
5. Increase the hull roof strength.
2. Turret:
1. Develop reliable protection against 88 mm shells with the muzzle velocity of 1000 m/s.
2. Improve the robustness of the gun mount.
3. Strengthen the top of the turret.
4. Develop a method of protecting the turret ring from shells.
3. Put KDLVT brand steel into production for IS-3 tanks.
2. Prototypes:
1. T-54 tank
1. Determine the armour that will protect the hull and turret from 75 mm and 88 mm shells with the muzzle velocity of 1000 m/s.
2. Improve the shape of the hull from the point of view of robustness and shell resistance.
3. Improve the armour of the turret to the point that it resists shells as well as the front of the hull.
4. Develop armour screens for the T-54 to protect it from HEAT shells up to 105 mm in caliber inclusive and Faust type anti-tank rockets.
5. Develop a robust track and track pin (increase track life to 3000 km).
6. Investigate the optimal location for ammunition in the tank.
2. 701 tank
1. Determine the type of turret and hull armour that would will protect the hull and turret from 88 mm shells with the muzzle velocity of 1000 m/s and 122 mm shells with the muzzle velocity of 800 m/s.
2. Remove all weak spots revealed during gunnery trials of the 701 hull.
3. Improve the armour of the turret to the point that it resists shells as well as the front of the hull.
4. Develop armour screens for the 701 tank to protect it from HEAT shells up to 105 mm in caliber inclusive and Faust type anti-tank rockets.
5. Develop a robust track and track pin (increase track life to 3000 km).
3. Experimental work:
1. Complete research on tank armour up to [illegible] thick. Compare the resistance of heterogeneous and homogeneous armour to 75, 88, 122, 105 and 128 mm shells at angles of 0 degrees, 30 degrees, 45 degrees, and 60 degrees.
2. Develop rolled and cast armour that can protect from the following shells
   88 mm at 1000 m/s
   105 mm at 900 m/s
   122 mm at 800 m/s
   122 mm at 1000 m/s
   128 mm at 900 m/s
   128 mm at 1100 m/s
1. Homogeneous
2. Cemented
3. Surface hardened with high frequency current
4. New design
3. Develop methods of connecting tank armour up to 300 mm thick.
4. Develop methods of protecting tanks from Panzerfausts, HEAT shells, and grenades. Test these methods on medium and heavy tanks.
5. Develop methods of protecting the floor of tanks and SPGs from anti-tank mines.
6. Develop automatic welding with austenitic electrodes. 
7. Develop new types of austenitic electrodes that do not cause cracks in metal when welding.
8. Develop a quenching technology that will prevent cracks on highly hardened armour.
9. Develop steel for tank and SPG suspensions and design components to be resistant to HE and HEAT shells.
10. Develop identical technical requirements for non-armoured tank and SPG components.
11. Develop a unified method for controlling suspension raw materials.
12. Develop instructions for welding tank and SPG hulls.
13. Revisit the technical requirements for development and testing of armour during peace time.
14. Process the materials on armour and tank metallurgy retrieved from Germany and present a report with conclusions and recommendations."

CAMD RF 38-11355-3077

A few notes on this document. "Tank 701" is more commonly known as "Object 701", and eventually became the IS-4. Also, fans of comparing gun penetrations may skim over this document, but they should not. While this document doesn't mention any numbers, it mentions the protection from the 88 mm gun with the muzzle velocity of 1000 m/s (88L/71 KwK 43 in the Tiger II) as a requirement for light (what a lofty goal!) and medium vehicles, but protection from the 122 mm D-25 is already in the domain of the heavies. What a future-proofed gun the D-25 was! 

Izhor Steel

"Homogeneous tank armour from new silicon-manganese-molybdenum Izhor factory steel (IZ type)"

RGASPI 558-11-150

"To the People's Commissar of Heavy Manufacturing, comrade S. Ordzhonikidze.

Explanation note on homogeneous tank armour made from new Izhor factory steel (manganese-silicon-molybdenum "IZ" type steel).

Until the middle of 1932, tank armour produced at the Izhor factory was made from chrome-nickel-molybdenum steel, containing 0.8-1.2% chrome, 4-5% nickel, and 0.4-0.6% molybdenum. This steel was very expensive, as it required a large amount of expensive imported components. The need for high quality, and, at the same time, cheaper and independently produced armour forced the factory to perform research into types of steel based on domestically produced compounds. 

A step in the right direction was achieved with silicon-chrome "PI" type steel, containing no imported components other than chrome. "PI" steel was proposed to two factories, ours and Krasniy Putilovets. It was successfully adopted by our factory. However, the "PI" steel could not fully satisfy our needs, as the high chrome byproducts could not be used directly in production of armour, and, when used in other manufacturing processes, resulted in low quality products. 

This forced the factory to explore new types of steel, which combined high toughness and maximum independence from imports with reasonable byproducts. Research work at the factory discovered such a steel at the end of 1932. It was a manganese-silicon-molybdenum steel with the following composition:

• Carbon: 0.29-0.4%
• Manganese: 1.1-1.8%
• Silicon: 1.3-1.8%
• Molybdenum: 0.3-0.5%
• Phosphorous and sulphur: 0.035%

IZ steel (IZ: Izhorskiy Zavod) was extensively researched in our factory. Research was performed in 1932-1933, first on steel cast in the electric furnace, later in a Martin furnace. This research revealed the high armour and mechanical qualities of the IZ steel, and it became necessary to test its combat and manufacturing properties on a wide scale.

In the end of 1933, IZ steel was used for T-35 tanks, in 11 hulls. The amount of defective plates was deemed acceptable for a new type of steel. The number of defective plates was less than with "PI" type steel of equal thickness. However, armour made into hulls showed cracking defects.

These defects are caused by additional stress that the plate experiences during welding. This is especially noticeable in complicated welding processes, or when high hardness plates are being welded. The requirement for high hardness plates (2.7-2.9 mm Brinell diameter) was from an old RKKA request, since, at the time, it was the only way to achieve required toughness.

The factory processed and used high hardness steel according to those requirements, which was one of the main reasons for cracks on IZ steel T-35 hulls. Further research showed that it was possible to use softer steel (up to 3.1 mm Brinell diameter) without loss of toughness. The reduced hardness increases the ductility of the metal, which reduces cracks on the hulls after welding.

All of this was confirmed when 5 hulls for the T-37 amphibious tank were assembled at the "KES" factory in Podolsk. Unlike the hulls produced at the factory with KO type steel, the IZ type steel hulls had no cracks at all. 

In April-May of 1934, an experimental batch of 150 welded and riveted T-26 hulls and 42 welded T-37 hulls was produced. The factory has already mastered the new steel and production of armour from it. Despite the difficulty of using new steel, defective product at all stages of the process, as well as product found defective during shooting and crack inspections, was no higher than for PI steel in 1933, and much lower than for PI steel during its trial period. The production data from the most difficult period in the steel's use gives no doubt that tank armour should be produced from IZ steel. This was once more confirmed when the factory held a general trial of armour and armoured hulls produced from IZ steel in order to finally determine the service quality of armour made from it. The trials were held as follows:

A: Armour trials

1. Bullet-proofness of 6, 7, 8, 9, 10, 13, and 15 mm armour from 29 batches, mostly forged in Martin furnaces.
2. Shell-proofness of 15 mm thick armour, which is the armour mostly used in T-26 hulls.
3. Bullet-proofness of armour in very low temperatures (-20, -30, -50 degrees,) and very high temperatures (+100 degrees).

B: Armoured hull trials

1. Bullet-proofness of the T-37 hull.
2. Shell-proofness of the riveted and welded T-26 hulls.
3. Effects of low temperatures (-50 and -70 degrees) and sharp temperature changes (from -50 to -70 degrees, and from +90 to +130 degrees) on cracking and deforming of riveted and welded T-26 hulls.
4. Bullet-proofness of a riveted T-26 hull subjected to alternating heating and cooling.

All of these trials were successfully passed by IZ steel armour. This finally confirmed the necessity of producing tank armour using this type of steel. Precise details on testing are recorded in documents with participation from representatives from the RKKA UMM, Armour Council of the NKTP, and the Central Institute of Metals (see the attachment "Materials on the general trials of IZ steel armour"). The main results are given below, along with illustrations.

The data from the research work (composed into a special report), and results from wide use of IZ steel in production, as well as these armour trials allow the following characteristics of main IZ steel qualities to be determined, compared to PI steel.

1. Mechanical qualities: the toughness qualities (resistance to tearing and proportionality limit) for IZ and PI steels is approximately the same. Ductility properties (resistance to blows, compression, and bending) shows that IZ steel is more ductile.
2. Bullet and shell resistance: IZ armour of lower hardness resists bullets just as well as PI steel, and resists shells better than PI steel, giving a more favourable penetration type in the latter case.
3. Armoured hull properties: trials consisting of alternating freezing both types of T-26 hulls to low temperatures (-52 to -70 degrees) and heating them to high temperatures (+90 to +130 degrees), followed by heavy gunfire did not result in cracking defects or a reduction in toughness. This indicates that IZ steel is suitable for use in various climates, and that it is unaffected by sudden temperature changes.
4. Technological and economical advantages of IZ steel: due to the impact of high chrome byproducts on the quality of steel, PI byproducts cannot be used for production of high quality products such as tank armour. The factory was either forced to sell these byproducts at a very low price or use them for lower quality products (pipes, frames for locomotives, etc). No doubt, these chromed byproducts also reduced quality of the latter.
   With IZ steel instead of PI steel, the factory can solve its byproduct issue, since IZ byproducts may be used to produce high quality components. The factory will reduce its consumption of metals, and increase the quality of products produced at the factory. Additionally, the byproducts contain molybdenum, an element that does not burn out during casting, and the re-use of these byproducts will increase the factory's demand for ferromolybdenum. All this allows reduction of costs and increase in quality.

In conclusion, the manganese-silicon-molybdenum IZ steel is no worse than PI steel in its toughness, climate resistance, and mechanical qualities, and has a series of advantages over it. These advantages include the possibility of reusing all byproducts of the casting process and returning molybdenum into new casts.

Aside from this, the new steel guarantees mobilizational readiness of all factories to a much higher degree due to the production process and the materials used, as well as guarantees equal toughness at lower hardnesses.

Taking all of the above into account, the Izhor factory insists that the issue of IZ steel in the production of tank armour be explored as soon as possible.

Attachments: photo album with 40 photographs.

Signatures

June 10th, 1934"

RGASPI 558-11-150

The following pages contain technical details. The first is acceptable amounts of carbon and manganese in the steel. The graph is pretty hard to read, but someone was nice enough to write out the composition on the top in large letters:

• C: 0.29-0.4%
• Mo: 0.3-0.5%
• Mn: 11-18%
• P and S: 0.035%
• Si: 1.3-1.8%
• Cr: 0.3%

The next page is the numeric results of all those test above, which wouldn't really be interesting to anyone that's not a metallurgist, or anyone at all with nothing to compare them to. After that, photographs of trials: tearing resistance, compression resistance, impact resistance, bending resistance, microstructures under various conditions. These are probably also not interesting, but, as always, ask if you need them. The following section is more interesting to us: armour properties!

Bullet-proofness testing was done with 7.62x54r armour piercing AU model 1930 rounds and with regular lead rounds at various distances. Here are some photos.

26 AU armour piercing bullets at 26 meters against a 15 mm plate, no penetrations. Plate front is shown on the top, plate rear on the bottom.

20 AU bullets against a 13 mm plate from 200 meters, no penetrations. 

36 AU bullets from 450 meters against one side of a 10 mm plate and 17 regular bullets from the other side at 50 meters. No penetrations.

9.3 mm plate, 20 AU bullets from 570 meters and 14 regular from 14 meters. No penetrations. 

I think you get the idea, so I'll stop posting pictures and only post more results. An 8 mm plate cannot be penetrated from 600 meters by an AU bullet or from 50 meters by a regular bullet. One bullet causes an indeterminate penetration (penetration due to the same point in armour being struck multiple times). A 7.5 mm plate also resists regular bullets from 50 meters. A 6.4 mm plate can resist the bullet from 150 meters. 

Now we get to the temperature controlled trials. The next photograph is of the armour plate in a freezer (it still looks the same). 

The frozen armour plate after being shot at and thawing. No penetrations from either bullet type at 50 meters, two inconclusive penetrations. Another plate with a different type of weld goes through the same process, with no penetrations (not even inconclusive ones). Another type gets one inconclusive penetration. 

Next, we get to the cooling and trials of entire hulls, with slightly more interesting pictures.

Here is a T-26  hull in a freezer. The label helpfully points out that it is covered in snow. The record at the bottom shows the temperatures that the hull withstood: -10 when inserted into the freezer, frozen to -70 over 4 hours, and then warmed up to -60 degrees over 8 hours. The details for heating are on the next page. The hull was heated up to 90 degrees over 4 hours, and then cooled to 35 over 8 hours. 

Same thing for the riveted hull. The pictures shows frost on the side. The hull was at a balmy -8 when placed into the freezer, cooled to -57 over 4 hours, and warmed to -52 over 8 hours. It was then heated to 120 degrees over 3 hours, and cooled to 65 over 9 hours.

Both hulls were then sprayed with armour piercing bullets from a DT machinegun at 50 meters. The welded hull developed one 35 mm long shallow crack. The riveted hull developed no cracks. 

Next is the T-37 hull. The hull was shot at with a Maxim machinegun, using 230 regular bullets at 50 meters and 114 armour piercing bullets at 570 meters. No penetrations were found. 

Photographs of the T-37 hull before trials and various angles after trials.

Seems that this new miracle steel of theirs was pretty good. IZ steel in thicknesses between 4 and 20 mm was used until at least the start of the Great Patriotic War.

German Armour Quality

During WWII, the relations between Britain and the USSR have been quite close. Aside from material aid (the British sent Lend-Lease tanks and equipment, the Soviets sent captured German tanks and their own samples), the two countries exchanged intelligence. Here is one of many such exchanges, from CAMD RF 38-11355-2704:

"Tendencies in the manufacturing of German armour plates (excerpts from the report prepared by the Head of the Main British Tank Development Directorate)

The testing of a Tiger tank recently brought to England showed a deviation from typical German armour protection techniques. None of the armour was surface hardened. The hardness on the Brinell scale is as follows:

• Thin horizontal plates (26 mm thick): 298-343
• Thick nearly vertical plates: 257-310

The fact that the armour is no longer surface hardened, and has a relatively low Brinell hardness, is very important. It must be noted that this change coincides with the appearance of new German heavily armoured tanks: Tiger, Panther, Ferdinand. Until now, no German tank had armour thicker than 50 mm.

The deviation from existing practices is explained by the following reasons, or their combination.

1. Economic reasons. It is very possible that the very amount of armour overloaded the German capacity to manufacture it, and Germany was forced to utilize heavier manufacturing, usually tasked with manufacturing simple armoured plates. There might be a shortage of equipment capable of processing thick armoured plates.
2. Mechanical finish problems. The three aforementioned vehicles have interlocking armoured plates to increase the strength of the welds. Regular step connections were preserved. The combination of these two connections reduced the ability to produce a large number of armoured hulls. Perhaps the softer plates were introduced to remedy these problems.
3. Ballistic factors. The three aforementioned vehicles were built for the purpose of long ranged combat. It is possible that the enemy introduced softer armoured vehicles knowing that the Allies use armour piercing capped shells. Use of these shells against soft armour is suboptimal. If soft armour continues to be used, we must explore the question of ballistic caps. However, it is necessary to collect more information, as this armour could still be surface hardened. 

It is necessary to examine a Panther tank and perform experiments on armour of Tiger tanks built later than the one mentioned in this report."

The report came out in January of 1944, so not many Tigers were built after that. The Americans, meanwhile, tested the armour of the Panther. Their findings spoke rather poorly of German manufacturing. Their findings were the same as what any of my readers have already seen: German armour is of poor toughness, and their welding seams have a tendency to burst under pressure.

Soviet 57 mm Guns

The Red Army, in its anticipation of hilariously over-armoured enemy tanks realized that the penetration of the F-34 gun was lacking. That is why, in 1941, Grabin's 57 mm ZiS-2 gun was adapted to the T-34 (and, in theory, T-34M). A shorter version of the ZiS-2 gun was named ZiS-4, and put into the T-34. The resulting tank, currently known to many as "T-34-57", appeared in documents as "T-34 with 57 mm gun", "T-34 with ZiS-4", "T-34 tank destroyer", or any combination of the above. Since the F-34 was already capable of defeating any enemy armour at 2000 meters, not very many of these tanks were made. CAMD RF 38-11355-323 lists 10 such tanks being sent from factory #183 to Vladimir to form the 21st Tank Brigade.

ZiS-4 57 mm gun model 1941

T-34 model 1941 with a 57 mm gun

In 1942, the Tiger hit the battlefield, and GABTU suddenly remembered this thing they had going pre-war. The 57 mm gun program was revived. A new and improved ZiS-4 was designed to fit the new and improved T-34 model 1942 turret.

ZiS-4 57 mm gun model 1943

T-34 model 1942 with a 57 mm gun

Four experimental T-34 tanks were built in June-July of 1943. However, at that point, work on 85 mm tank guns began, so no one was quite sure what to do with these odd ducks. CAMD RF 38-11344-1755 tells of their uninteresting fate:

"According to the ciphertext from Major-General comrade Vershinin, four T-34 tanks with the ZiS-4 artillery system were sent to the Gorohovets proving grounds, where, after trials, one tank was sent to factory #92, and the rest sent back to factory #183.

Please advise what to do with these tanks."

Notice how the new gun is still "ZiS-4", and not "ZiS-4M". 

The tests at Gorohovets were concluded on September 15th. The above document is dated October 11th. The T-34 armed with the longer S-54 76 mm gun was tested at Gorohovets around the same time. At this point, the first T-34-85 was already being built by factory #183, so new 57 and 76 mm artillery systems for the T-34 were discontinued. A project to stick the ZiS-4s already produced into SU-76es was also launched, but didn't really go anywhere. 

However, despite the 57 mm gun never quite making it on a tank, it was quite handy in its ZiS-2 form as towed artillery. Here's how it performed against the Tiger, from CAMD RF 38-11377-12:

"Target: side. Distance: 800 meters. Result: penetration, 110 mm in diameter. A fragment, 190 mm by 210 mm broke off on the inside. The welding seam connecting the side and rear plates burst in an area 500 mm in length.

Target: side. Distance: 1000 meters. Result: penetration, 110 mm entrance, 140 mm exit. Fragment broke off on the inside, 140 mm by 110 mm."

The gun is more than capable of taking out the Tiger from the side. Let's try the turret.

"Target: commander's cupola. Distance: 1000 meters. Result: penetration, breach 85 mm by 75 mm. The cupola was torn off.

Target: turret. Distance: 1450 meters. Result: dent, 110 mm in diameter, 70 mm deep. A 20 mm cracked bump formed on the inside.

Target: turret. Distance: 1450 meters. Result: dent 49 mm deep, 125 mm in diameter, with a jagged surface. On the inside, a 15 mm bump.

Target: turret. Distance: 1450 meters. Result: dent, 110 mm in diameter, 15 mm deep."

The gun is less capable against the turret (although they probably should have closed in a bit after the first few bounces). Shooting at the cupola is an effective tactic.

"Target: upper front plate. Distance: 500 meters. Result: insignificant indent, the shell ricocheted into the driver's vision port.

Target: upper front plate. Distance: 500 meters. Result: dent, 90 mm in diameter, 20 mm deep. The welding seam is destroyed throughout its entire length. 

Target: lower front plate. Distance: 500 meters. Result: dent, 120 mm in diameter, 35 mm deep. Two 70 mm cracks in the dent. The welding seam is destroyed on a length of 500 mm."

Seems like the front is a tough nut to crack. The welding seams are failing one by one, as usual. With enough hits, the front plate is bound to fall off!

Conclusions: "As a result of shooting at the Tiger tank with the domestic 57 mm gun, it has been established:

a) The AP shell penetrates the 82 mm thick side at 1000 meters.

b) The AP shell does not penetrate the 100 mm thick front at 500 meters."

Not fantastic results, but not surprising. The results are better than the British 6-pounder gun of the same caliber, at least.

The Tiger II test document does not mention the 57 mm gun, but that doesn't mean it couldn't take one out. A Tiger II with numerous breaches from a 57 mm AT gun was displayed during an exhibition of captured vehicles.

The text reads: "Armour: 100 mm" on the turret and "armour: 85 mm" on the hull. Two arrows on the turret point at breaches, and are labeled "the armour was penetrated by a subcaliber 57 mm shell from an anti-tank gun".

F-34 vs German Tanks

Many sources point to the gun of the T-34 as a weakness, as it was incapable of harming a Tiger at over 500 meters. While this is true, it is misleading. While the T-34's 76.2 mm F-34 AP shell was, indeed, not very good against a Tiger, it was much more than enough against the overwhelming majority of German tanks. This article contains the results of testing its AP and HE shells. The "Report on the shooting of German tanks with AP and HE shells from tank guns" (CAMD RF 38-11355-832) contains the data we need.

First up, as always, is the Pz 38(t). The first shot is fired from 800 meters, with a devastating effect. The 76 mm shell penetrates the turret platform from the front, tears off the front plate, and shatters it into pieces. The fragments then enter the crew compartment.

The testers switch to an HE shell. They fire at the front of the tank hull from 800 meters. The front plate is bent by 40 mm. The welding seam holding it front plate burst (300 mm in length). The two front wheel carriers are torn off (each is held on by 4 bolts). 12 bolts popped off the front armour plate.

The next shell is aimed at the front of the turret from the same distance. The front armour plate is torn off in an area right of the gun. Fragments of the front plate enter the turret. The next shot is aimed at what's left of the turret platform from 900 meters. The remainder of the front plate is shattered by the HE shell, and the pieces fall inside the tank.

Another shot from 800 meters, this time at the side. A 200 mm breach is formed in the outer armour plate, 300 mm breach in the inner one. A shot from 950 meters makes a breach 100 mm in diameter, and results in 90 mm long cracks running through the side armour.

The next target is the side of the turret, from 950 meters. The turret is torn off, and displaced 150 mm. The turret ring is destroyed. The right side of the turret is destroyed.

The next target for the F-34 is the PzIII. The loader switches back to AP. The gunner fires from 900 meters. The front armour is penetrated (entrance diameter 120 mm, exit diameter 165 mm). The tank's gearbox is destroyed. Notice the large diameter of the breach compared to the shell's caliber. This is a sign of over-hardened or poor quality armour.

The next target, again from 900 meters, is the sloped portion of the front armour. The armour plate is fragmented in an area up to one meter away from the breach. The welding seam holding the plate bursts over a length of 1.5 meters. The armour fragments enter the crew compartment.

Another shot from 900 meters, this time from the side. A torsion bar limiter is torn off. A hatch is torn off. The tire of one of the wheels is torn off.

The testers switch back to HE. The first shot from 900 meters shatters the left side of the turret platform over a span of one meter. Another shot makes a breach in the lower hull 240 mm in diameter, as well as a breach 300 mm in diameter in the bottom of the PzIII. An idler is knocked off. The gas tank is punctured.

Another shot makes a 400 mm breach in the side of the tank, knocks out the rear wheel shock absorber, and damages the engine and radiator with the fragments. Another shot at the right side of the turret tears off the turret hatch, destroys the turret ring, and bends the side armour by 60 mm. Fragments of the armour "damage everything inside the turret". The last shot bends the side armour by 50 mm, tears off the right side of the turret platform, and shatters it into three pieces.

Conclusions: "The 76 mm AP shell penetrates the 60 mm of front armour at 900 meters. We did not test larger distances. The 76 mm HE shell destroys the side armour and turret from 900 meters."

The PzIV is tested next. Its front armour is penetrated at 500 meters (entrance diameter 90 mm, exit diameter 100 mm). From 800 meters, another penetration. The front armour plate is shattered into two pieces. Another shot from 800 meters penetrates the front. The testers switch to firing at the side at 800 meters.

The side is penetrated. The 20 mm armour screen is torn off the bolts that hold it. The shell keeps going, and penetrates the other side of the hull, and its armour screen. Total penetration is 80 mm. Another shell penetrates the side, but only one side this time. It knocks off the wheel carrier.

The gunner aims at the turret. The hatch of the turret is torn off with a direct hit. The side of the turret bends inwards 50 mm. Another shot impacts the commander's cupola, tearing it off, and throwing it 5 meters. The hatches on top of the cupola are also torn off, and thrown 30 meters. Another shot to the side of the hull forms a 130 by 350 mm breach.

Conclusions: "The 76 mm AP shell can penetrate the front of a PzIV at 900 meters. We did not test larger distances. The 76 mm HE shell destroys the side of the turret and hull at any range."

From conclusions of the document:
"The 76 mm long-range HE-fragmentation steel grenade fired from a 76 mm gun (F-34) model 1940 installed in a T-34 tank, on impact with the Czechoslovakian 38t tank, side or rear 30-20 mm German tanks PzIII, StuG, and PzIV, destroys armour plates from 1000 meters, damaging the tank and crew with the fragments.
The 76 mm AP shell, when fired from a 76 mm gun (F-34) model 1940, penetrates the front armour of German tanks PzIII, PzIV, and Pz 38(t) from 800-1000 meters. The penetration ability from over 1000 meters was not checked.
...
The 76 mm model 1940 (F-34) gun is an effective weapon against all German tanks, based on its AP penetration and HE shell destructive properties."

According to calculations of NII-48 in topic 2VV-2 "Investigation of the armour of tanks of the German army" (CAMD RF 38-11355-778), the following are the distances at which an F-34 can defeat the armour of a Pz 38(t):

• 90 degrees
• Turret and hull front: 1970 meters
• Turret platform front: 1970 meters
• 80 degrees
• Turret and hull front: 1970 meters
• Turret platform front: 1940 meters
• 70 degrees
• Turret and hull front: 1900 meters
• Turret platform front: 1860 meters
• 60 degrees
• Turret and hull front: 1690 meters
• Turret platform front: 1600 meters
• 50 degrees
• Turret and hull front: 1320 meters
• Turret platform front: 1250 meters
• 40 degrees
• Turret and hull front: 880 meters
• Turret platform front: 840 meters
• 30 degrees
• Turret and hull front: 490 meters
• Turret platform front: 420 meters

Tactical diagram for a Pz38(t). The F-34 is shown as the double dotted line (front only)

For the PzIII, a much larger number of armour groups was tested, to the point where it would be massively inconvenient to transcribe the full chart (if you absolutely must have it, let me know), but here it is for a slightly angled tank, at 80 degrees:

• Upper front plate: 800 meters
• Lower front plate: 1800 meters
• Turret platform front: 1970 meters
• Turret front: 1970 meters
• Upper rear: 1940 meters
• Middle rear: 1900 meters
• "All other parts of the tank can be penetrated with a 76 mm AP shell at any distance, at any angle". 

The conclusions made are as follows: "The protection from 76 mm AP shells is unacceptable. Even its front is penetrable at 900-1200 meters when standing at 45 degrees, and exposing many more vulnerable parts."

Tactical diagram for a PzIII tank. The F-34 is shown as a dotted line for the front and back.

For a PzIV, similar conclusions (again, at 80 degrees):

• Side with armour screen: 2000 meters
• Turret and hull front: 1970 meters
• Turret platform front: 1970 meters
• "All other parts of the tank can be penetrated with a 76 mm AP shell at any distance, at any angle".

The conclusions made are as follows: "The protection from 76 mm AP shells is unacceptable. Even its front is penetrable at 1100 meters when standing at 45 degrees, and exposing many more vulnerable parts."

Tactical diagram for the PzIV tank. The F-34 is shown as a dotted line for the front and sides.

The same table is made for a StuG III, but only the front armour plate. The result is the same as a PzIII: vulnerable at 1970 meters, 1100 meters at a 45 degree angle.

CAMD RF 38-11355-776, a NII-48 article on domestic armour quality, also discusses experimental HEAT shells. These shells were capable of penetrating 30 mm of medium hardened armour and 45 mm of highly hardened armour at a distance of 1600 meters, at every tested angle (maximum tested was 45 degrees).

45 mm APCR

By 1942, the penetrative power of the Soviet 45 mm anti-tank gun model 1932/37 has ceased to be very impressive. After studying captured German 37 mm PzGr 40 shells, and French 47 mm Komissan shells, NII-24 developed two types of APCR shells for it: one with a 20 mm tungsten carbide core, and one with a 28 mm tungsten carbide core. The shells were also manufactured with highly hardened steel cores. The requirements for the project were "penetration of a 60 mm armoured plate angled at 30 degrees, at a distance of 300-500 meters". Let's see how well they managed.

45 mm APCR type 1 (28 mm core, left) and type 2 (20 mm core, right). CAMD RF 81-12042-69

I will skip the metallurgical data, and get straight to the good stuff: penetration and accuracy.

The theoretical penetration calculations, against armour at 30 degrees, were as follows:

• 0 meters: 80 mm
• 100 meters: 74 mm
• 200 meters: 69 mm
• 300 meters: 65 mm
• 400 meters: 60 mm
• 500 meters: 56 mm
• 600 meters: 52 mm
• 700 meters: 48 mm
• 800 meters: 44 mm
• 900 meters: 40 mm
• 1000 meters: 37 mm

In theory, the engineers met the requirement. At 400 meters, the shell penetrated 60 mm of armour. Let's see how that translates into practical penetrations.

"Armour plate: 50 mm, cemented. Shell type: 1. Core type: steel. Distance: 120 meters.

Result #1: dent. On the rear side, spalling 5-6 mm deep. The core is stuck in the armour plate.

Result #2: penetration. Diameter 60-80 mm entrance, 30-45 mm exit. Core is destroyed. The plywood behind the target has a breach 150 by 100 mm. 

Distance: 100 meters.

Result #1: Armour is not destroyed. A dent is formed on impact. The core is destroyed.

Result #2: Penetration. Entrance diameter 90-70, exit diameter 40-35 mm."

Well, the steel core APCR is inconsistent, to say the least. Let's see what tungsten can do.

"Armour plate: 50 mm, cemented. Shell type: 1. Core type: tungsten carbide. Distance: 700 meters. Result #1: penetration. Diameter of breach: 75-40 mm entrance, 35-45 mm exit. The plywood behind the target has a breach 160 mm by 110 mm. Similar results are achieved by shot #2.

Shell type: 2. Core type: tungsten carbide. Distance: 450 meters. Result #1: penetration. Diameter of breach 25-40 mm entrance, 20-35 exit. Plywood behind the target has a breach 80 by 100 mm. Similar results are achieved by shot #2."

Much better! Let's see how steel does against a thicker target.

"Armour: 60 mm, non cemented. Shell type: 1. Core type: steel. Distance: 100 meters.

Result #1: No penetration. A dent 40 mm deep is formed. The core shattered.

Result #2: No penetration. A dent 35 mm deep is formed. The core shattered."

And back to tungsten, with the same armour plate:

"Shell type: 1. Core type: tungsten carbide. Distance: 400 meters. Results #1 and #2: penetration. Breach size 40-75 mm entrance, [missing] exit. Plywood behind the target has a breach 400 mm by 150 mm. 

Shell type: 2. Core type: tungsten carbide. Distance  380 meters. Results #1 and #2: penetration. Breach size 25-35 mm entrance, 20-25 mm exit. The core shattered. First shot makes a breach in the plywood behind the target 50 by 80 mm, the second 80 by 80 mm."

At this point, the testers ditch steel, and only test tungsten for larger thicknesses.

"Armour: 80 mm, non cemented. Shell type: 1. Core type: tungsten carbide. Distance: 300 meters. Results #1 and #2: penetration. Breach size 50-90 mm entrance, 30-45 mm exit. The core shattered. 

Shell type: 2. Core type: tungsten carbide. Distance: 250 meters. Results #1 and #2: penetration. Breach size: 20-50 mm entrance, 20-18 mm exit. The core shattered."

These results are very promising, much better than the calculations. Let's see what happens against thicker armour.

"Armour: 100 mm, non cemented, at 0 degrees. Shell type: 1. Core type: tungsten carbide. Distance: 65 meters. Result: penetration. Breach diameter 65 mm entrance, 30-20 mm exit. The breach has fragments of the core stuck in it. The plywood behind the target is also penetrated.

Shell type: 2. Core type: tungsten carbide. Result: penetration. Breach diameter is a caliber."

This is very promising! Note the impressive thickness of the armour. The calculations have been very pessimistic, as the shell can penetrate 25% more armour than predicted. Such a shell can defeat a Tiger, provided the gun is close enough. 

Accuracy figures are also provided in the report. At 500 meters, the maximum deviation of type 2 shells is only 20 cm in either direction. Type 1 shells have poorer accuracy, with deviation of 42 cm vertically and 33 cm horizontally. The inaccuracy of type 1 shells is explained by their inconsistent mass. 

Something interesting to compare: along with captured German 37 mm shells, a document was captured describing them as only useful up to 300 meters. The realistic range for these 45 mm APCR shells is listed as 500 meters. Comparing penetration, the 37 mm PzGr 40 shells only penetrate a 30 mm armour plate at 30 degrees at 300 meters, and cannot penetrate a 40 mm plate. The 45 mm APCR shells could penetrate an 80 mm plate at 30 degrees at this distance. 

However, you may still be reeling from the suggestion that a 45 mm tank gun can take out a Tiger. A small caliber gun, on T-70 or even T-26 light tanks! Preposterous! Or is it?

CAMD RF 38-11377-12

"As a result of shooting the Tiger with a 45 mm tank gun, it is determined that:

• a subcaliber shell penetrates the lower side hull, 62 mm thick, at 350 meters.
• a subcaliber shell penetrates the upper side hull, 82 mm thick, at 200 meters."

CAMD RF 38-11377-12

"Photo #7. Penetrations from a 45 mm AT gun.
XX: penetration 20 mm in diameter, crack along welding seam 200 mm in length. Distance: 200 meters.
XXI: penetration 20 mm in diameter. Distance: 350 meters.

Photo #8. Penetrations from a 45 mm AT gun.
1: penetration, 30 mm in diameter. A crack formed from 50 mm from the breach to the edge of the armour plate.
5: penetration, 20 mm in diameter. Distance: 350 meters.

As a result of shooting at a Tiger with a 45 mm AT gun, it is determined that: 

• a subcaliber shell penetrates the lower side hull, 62 mm thick, from 500 meters.
• a subcaliber shell penetrates the upper side hull and turret side, 82 mm thick, from 350 meters."

Pretty impressive for such a small caliber!

American Guns vs German Tanks

The 1942 "Report on the shooting of German tanks with AP and HE shells from tank guns" contains testing of American guns against captured German tanks: the 37 mm M5 tank guns on the Lee and Stuart, and the 75 mm M3 gun on the Lee.

The first test subject is the Czech LT vz 38, also known as Pz 38(t). The first tank to shoot at it is the M3 Stuart, firing M-51 shells out of its 37 mm gun.

The first target is the front armour plate. At 50 and 100 meters, only one shell out of 5 fails to penetrate. Holes made in the armour are noticeably larger than the shell caliber (70-80 mm in one dimension). Next target is the turret platform. One shot at 400 meters, and one shot at 600, both penetrate. Next is the side of the turret, at 800 meters. Again, all penetrations. The second shot to the right side of the turret caused a crack 140 mm long. The final shot is at the front of the tank, at 100 meters. It strikes the MG, and knocks it out. 

Conclusions: "Front armour, 50 mm thick can be penetrated starting at 100 meters. Sides of the tank, 30 mm  thick, can be penetrated at 800-1000 meters."

Regrettably, the photo quality isn't fantastic, but you can see that, in the top photo, the MG ball was knocked out. The second photo shows the shells extracted from the tank. Like all American shells, they mostly retain their shape, even after penetrating armour. 

That's it for the vz 38. The armour plates are overly hardened, as we've seen on the mid-late war German vehicles. This causes the plates to crack, spall, and fall off.

Next up for testing is the StuG. The 37 mm American gun, once again, gets first dibs.

Shots at 100 meters at the front plate. All 3 go through, one shot damaging the braking mechanism. The Germans' early war armour is ductile, giving breaches not much larger than 37 mm in diameter. The next three shots are fired from 150 meters. All fail to penetrate the armour, making dents. Another shot is fired at the side, from 800 meters, penetrating the gas tank. 

The top photo shows the StuG after taking a penetrating hit from the side. The bottom photo shows the shells. Shells marked 1 were the ones that penetrated the hull. The shell marked 2 was one of the shells fired from 150 meters that did not penetrate.

It's the Lee's turn next, firing HE shells from its 75 mm gun. 

The first shot, from a distance of 800 meters, hits the front armour. The 50 mm thick plate shows no signs of damage. The 30 mm thick cover of the transmission is dented 8 mm down, and the welding seam suffers a rupture 80 cm in length. The right half of the transmission hatch is torn off. Subsequent shots are fired at the side of the StuG.

The second shot, also at 800 meters, hits a wheel, damaging it. A second shot tears off the rubber tire. Even after two direct hits, the wheel is still functional. A shot to the side leaves a negligible mark on the armour and damages the gas mask holder on the inside. A torsion bar carrier is torn off. 

Closing in to 600 meters, the Lee shoots at the radio bay. The armour plate is bent inwards 8 mm. A crack forms along the welding seam, 1.5 meters in length.   

Further shots from 600, 500, and 400 meters keep slightly bending the armour, damage 3 track links, and a roller. 

Conclusion: "The 75 mm HE shell from the M-3 Medium tank does not penetrate or destroy a StuG from 800, 600, or 400 meters."

This is it for American guns in this report. Here are the applicable conclusions:

"The 37 mm American shell, after penetrating 50 mm or armour at 100 meters, shatters into 3-5 fragments. The tip of the shell is usually intact. At 150 meters, the shell usually makes a dent 40-50 mm in a 50 mm armour plate and breaks into 3-5 fragments.

...

Scattering of shells from the 37 mm and 40 mm guns does not exceed the size of a StuG at 800 meters.

...

Of all the gun sights tested, the American gun sight on the M3 Light and M3 Medium led to the worst accuracy.  

...

Of all low caliber shells, the American 37 mm shell is of the highest quality, and provides the most penetration. "

Another report also tests the Sherman's gun against the Tiger, which I covered earlier.

The American M1A1 76 mm gun, mounted on an M18 Hellcat (serving in the Red Army under the name T-70 Ved'ma, or Witch) was tested against a Tiger II. Firing M-62 APC shells, it achieves the following results: 

"The armour piercing shell of the American 76 mm gun penetrates:

• The side of the hull at 2000 meters.
• The overtrack hull at 1500 meters.
• The turret side from 1500 meters."

Bovington: T-34 and KV-1 impressions

Just like the Americans, the British received a T-34 and a KV-1 tank for testing. Their response to the tests was radically different.

CAMD RF 38-11355-2222

"Please advise representatives of the purchasing commission in England what to do regarding building T-34 and KV tanks. If the English really want to mass produce these tanks, I would like to know what changes they make to their construction and keep track of their efforts."

Instead of merely taking the parts of the T-34 and KV like the Americans did, the British decided to produce clones of the tanks. Not surprising, given that the state of British tank production in mid-WWII was a bit delayed. The results of the tests were discussed at the "Scientific-Investigative Tank Proving Grounds" (perhaps Bovington?) on January 6th, 1944.

"Upon arriving at the proving grounds, we were invited to a meeting room where the administration of the grounds gathered, military and civilian, about 15 people. The chief of the proving grounds introduced them as the heads of various groups and departments. All of the military men were majors and lieutenant-colonels. These people had prepared questions from various areas for us.

We were asked questions regarding the construction of the vehicles, their materials, armament, usage, etc.

This report contains several questions about the armament and construction of the tanks. The following issues were also of interest to the English, asked of me outsides the office of the chief.
1. After shooting a gun of a caliber larger than 75 mm, gases exiting the barrel obscure the line of sight, and make it impossible to view your target for two seconds. To observe the path of the shell, we had to open the hatches.
Our response: this is an issue that can only be evaluated by the tank gunners themselves. In any case, a shell with a tracer is seen better than one without.

2. The gas tanks of the tank are located on both sides of the turret, which is a hazard in the fighting compartment.
Our response: we put additional gas tanks wherever possible. Perhaps you will find a better place for them.

3. The loader's seat does not fold down.
Our response: this is an issue that can be easily fixed if you so wish it.

4. Tanks do not have equipment for indirect fire.
Our response: these tanks were not built for the purpose of indirect fire.

5. Can a KV tank with a 6 inch howitzer provide indirect fire?
The question is asked knowing about the existence of such a tank in the Red Army [Note: the KV-2 matches the description of a "KV tank with a 6 inch howitzer"]. The English have known of its existence for a while. In early 1942, Major Donnington of the Artillery Depot asked about a KV armed with a 6 inch howitzer. Based on this knowledge, we answered that the tank in question is also not designed for indirect fire.

The questions asked by the English are few. As for their content, we consider 1, 4, and 5 relevant.

The first question regarding the tracer being obscured by gases is relevant, but is resolved by experience gained while using the tank. If this event occurs, then it appears that the training of our gunners is high enough that they are capable of performing effectively despite this drawback, which we think would be difficult to remove.

Questions 4 and 5 are also relevant. The question of indirect fire is asked by the English for a reason. Their officers insist that the manner of operations that their tanks carry out requires the ability to use tanks as artillery [illegible] terrain on the Italian front led them to use tanks as artillery batteries. They suppose that our T-34 and KV tanks, if mass produced, will be supplied with the necessary equipment.

Additionally, in our conversations, we have learned that:
a) the T-34 and KV vehicles will be produced for the British army. The former will be equipped with a 17-pounder, the latter with a 6 inch howitzer.
b) the tanks will be built with an improved gearbox and differential clutches.
c) the KV air pumps will be improved. [Note: the KV the British got had a defective air pump]
d) the tanks will be equipped with centrifugal air filters that will draw air from the transmission compartment. This is explained as follows: if you take air from behind the tank, it will contain dust kicked up by the tank. If you draw air from the transmission, the air purity reached is 100% ideal.
e) the welding will be performed with electrodes made from high hardness steel, which will result in welding seams being as robust as the armour plates.

English critique of the armament of our tanks:

Their opinion of our armament is good. This could not be otherwise, as their newest Centaur tanks were just recently equipped with 75 mm guns with ballistics equivalent to the American 75 mm gun on the Sherman tank. Currently, the largest caliber tank gun the English posses is the 6-pounder (57 mm). If you further recall the Churchill tank with a 2-pounder gun, you could not expect any other evaluation of our guns. The English themselves admit that arming the Churchill with a 2-pound gun was a poor idea.

The English, however, suggest that 76 mm is not enough for a KV tank, and propose to install a 6 inch howitzer, the ballistics of which were sent to NKVT earlier.

The T-34, on which they adore both the gun and the sloped front armour, is deemed to have satisfactory armament for a tank of that type. However, the English wish to outdo us and replace it with a 17 pounder gun.

Re-armament requires some modifications, and will take time, but, taking into account the manufacturing power of England and her dominions, we could very well see a T-34 with a 17-pounder gun and a KV with a 6 inch howitzer in our time. The fact that the English expect to produce our tanks is almost not hidden from us. This was established in conversations with workers of the Scientific-Investigative Tank Proving Grounds, and is backed up by other evidence. For example, when visiting an English gun factory near Liverpool, journalist [illegible] was informed that the factory is getting ready to produce 17-pound guns for T-34 tanks, that the English will soon produce."

Yuri Pasholok mocked up the following images:

Well, this is quite unexpected. As we all know, the British decided to go with American tanks, but put a 17-pounder into the Sherman and M10 anyway. This isn't exactly unprecedented in international tank building.  The T-34 itself is a distant relative of the work of American engineer Christie. The Soviets produced a large amount of T-26 tanks based on Vickers 6-ton tanks. The German PzI was also heavily influenced by the British Carden Loyd tankette design.

Let's take a look at the tanks themselves. The T-34 is no stranger to having large guns fitted into its turret, but what about the KV? The KV-2's 152 mm gun required a much larger turret. The British were going to have a hard time with a small KV turret, if not due to the turret ring (the KV-1 and KV-2 have the same turret ring), then to the gases and crampedness that such a contraption would introduce. The British are no strangers to cramped designs (I still wonder how they fit three people into some modifications of the Valentine turret), and the gas problem would be solved by an open-top turret. Perhaps this is why they were asking about indirect fire.

The Soviets, in a similar move, fitted the KV-1 with a 122 mm U-11 howitzer, designating this prototype KV-9 in 1942. It was not mass produced. By 1943, they arrived at the same decision as the British: 76 mm is not enough for a heavy tank, considering that the T-34 carried the same caliber gun. While the replacement heavy IS tank had a 122 mm gun, some proposed versions had a 152 mm howitzer.

Soviet 85 mm Guns vs Tigers

When the Germans encountered the thick armour of Matildas at Arras, they lowered their 88 mm FlaK guns and used them to engage the British tanks. When faced with the Tiger's thick armour, the Soviets did the same. The AA gun chosen for this task was the 85 mm anti-aircraft gun model 1939. Let's see how well it worked against a Tiger.

"Target: side. Distance: 800 m. Result: penetration, breach size 350 mm by 230 mm.
Target: side. Distance: 1450 m. Result: penetration, breach entrance diameter 110 mm, exit diameter 380 mm. A fragment 700 mm by 92 mm by 82 mm was knocked off. Cracks 220 mm, 200 mm, and 180 mm in length developed."

Some pretty catastrophic spalling going on here. Recall that the T-34-76 had to close in to 500 meters to even have a chance of damaging a Tiger tank, even from the side. 

"Target: side. Distance: 1450 meters. Result: penetration, breach diameter 115 mm.

Target: lower front. Distance: 1000 meters. Result: penetration. Entrance diameter 150 mm, exit diameter 160 mm. An armour fragment 230 mm in diameter broke off on the inside. Three cracks, 300 mm long, developed. The welding seam is destroyed." 

More catastrophic spalling, this time in the front. More welding seams giving in under pressure. The testers then got optimistic, and moved out to 1500 meters.

"Target: upper front. Distance: 1500 meters. Result: dent 30 mm deep, 120 mm in diameter. Bump on the inside.

Target: lower front. Distance: 1500 meters. Result: the plate cracked from previous impacts by the 85 mm gun. Two pieces broke off: 500 mm by 240 mm and 800 mm by 200 mm."

The Tiger's overhardened armour cracks and falls apart after two hits to the lower front plate. A bit disappointing for a tank that has been made out to be invincible. 

"Conclusion: the armour piercing shell can penetrate the side of the Tiger tank, 82 mm thick, from 1500 meters, and the front, 100 mm thick, from 1000 meters."

These are certainly some excellent results. They appear to be confirmed in practice, since a Red Army document on tactics of Tiger combat notes that it can be penetrated from the front at 1000 meters, and from the side at 1450 meters. It is not surprising that an 85 mm gun with similar ballistics was placed first in the SU-85, then in a T-34, to make a dangerous enemy for any German tank.

Now, let's take a look at tests against the Tiger II. The D-5 gun is used in these, mounted on the SU-85 tank destroyer.

"Shot # 22. Target: upper front plate. Distance: 300 m. Result: dent, 200 mm by 125 mm, 50 mm deep (including remains of the shell that welded itself to the armour). A fragment broke off the other side of the armour, 300 mm by 250 mm, 85 mm thick."

As with a lot of shots at the Tiger II, even when the shell does not penetrate, the spalling takes care of the crew and internal components anyway.

For shots from the side, the data is presented in a different report (from which there is only a table in the summary report). From that table, the following conclusions are made:

"The AP shell from the domestic gun D-5-S penetrates: 

• the side of the hull from 1350 meters
• the over-track hull from 800 meters
• turret side from 800-1000 meters"

A T-34-85 fought several Tiger IIs from the s.Pz.Abt 501 at Ogledow. There were supposed to be 45 of these new tanks, but only 8 made the 45 km march. Oskin's T-34-85 destroyed 3 of the Tiger IIs in that battle. One of the tanks that was captured at Ogledow intact was the one that served as a test subject in the Tiger II penetration report.