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.

A Barrel Too Long

Rapid growth in power of tank and SPG guns continued throughout WWII. Designers of some nations achieved the increase in firepower through a harmonious increase of gun caliber and barrel length. Other schools of design preferred to keep the caliber, but significantly lengthen the gun. The second approach was very common for German armoured vehicles. This decision had both positives and negatives. It turned out to be not so simple to install long guns on medium tanks. The Panzer IV/70 is a good example of this. An attempt to create a more powerful variant of the Jagdpanzer IV gave the tank destroyer both new abilities and serious problems.

Heavy Trophy from the Kursk Salient

The relatively rare German heavy Panzerjäger Tiger (P) SPG, more commonly known as the Ferdinand, left a noticeable mark in history and in Soviet tank building. The name "Ferdinand" itself became denominative: Ferdinands were spotted on all parts of the front until the end of the war. In practice, only 91 vehicles were built, and the Ferdinand was only used en masse in the summer of 1943, during Operation Citadel at the Battle of Kursk. The Germans lost more than a third of these vehicles there.

Despite the fact that the Ferdinands (as well as the Elefant) were used very sparingly, they showed themselves as effective anti-tank guns. The Red Army command treated the child of Porsche K.G. and Alkett seriously. The appearance of the Ferdinand on the front lines reflected itself in the development of Soviet tanks, tank guns, and SPGs.

Comparative Penetration

"Conclusions

1. As a result of trials of D-25 (122 mm) and D-10 (100 mm) tank guns, the following penetration ranges against the upper front plate of the Panther tank were established:

Gun	Shell	Distance of complete penetration
122 mm D-25	Armour piercing	2000
100 mm D-10	Armour piercing	1200
German 88 mm gun (Ferdinand SPG)	Armour piercing	600
German 75 mm gun (Panther tank)	Armour piercing	No penetration

More Ferdinand Penetration Tests

You may recall two previous article where the Ferdinand's armour was tested: against the 152 mm ML-20 and 122 mm D-25. Today, thanks to Yuri Bakhurin, I bring you the results of the rest of the test.

First, we have the 45 mm gun. Naturally, it can't do anything to the Ferdinand's thick side. AP shells shatter when hitting the armour, cores from APCR shells sink into the armour without penetrating.

Next, the 6-pounder from the Churchill. Penetration is achieved at ranges of 300 meters, but firing from 500 meters yields little results. Shells either get stuck in the armour or shatter.

Now, the Sherman's turn. M-72 shells from the 75 mm gun cannot penetrate the side or rear armour. The M-61 shell fares better, penetrating the side at 500 meters.

Next, the Soviet 85 mm gun. These shells are easily able to pierce the side of a Ferdinand, causing spalling on the inside.

The proving grounds also had a Panther, and decided to see if it could take on a Ferdinand. Turns out, it could. The vertical front armour can be penetrated by the Panther's gun.

The front of the casemate, however, proved too tough of a challenge. The shells made 170-180 mm dents and could not penetrate all the way,.

75 mm APCR can penetrate even this tough armour.

Penetration through the side. Note the jagged outline of the hole, caused by spalling.

Spalling damage from the inside. The large hole is from an AP penetration, the small hole is from APCR penetration.

The Ferdinand had a chance to take revenge on the Panther. The 88 mm shell ricocheted, but led to a breach and spalling in a 300 mm by 250 mm area.

The results of these trials were used to compose this guide on fighting the Ferdinand.

IS-2 Modernization

"Conclusions on blueprings of the modernized IS tank

1. Armour protection

The front plate of the IS tank is cast from high hardness armour. The upper front plate is 100 mm thick and 60 degrees from vertical. When shot at by 75 mm gun model 1942 with muzzle velocity of 1000 m/s, or 88 mm model 1943 gun with muzzle velocity of 1000 m/s, it cannot be penetrated.
The ramming section of the hull can be penetrated with the following guns at normal:

1. 75 mm gun model 1942 with muzzle velocity of 1000 m/s: at a range of about 900 meters.
2. 88 mm tank, anti-tank or AA gun model 1936 with muzzle velocity of 810 m/s: at a range of 100-300 meters.
3. From the 88 mm gun model 1943 with muzzle velocity of 1000 m/s: at about 2500 meters.

The front slope of the turret platform is 130 mm thick and cannot be penetrated with the aforementioned guns.

The front part of the turret is 130 mm thick and cast from high hardness steel and can be penetrated by the following guns:

1. 75 mm tank gun model 1942 with muzzle velocity of 1000 m/s: at a range of 1100 meters.
2. 88 mm tank gun model 1943 with muzzle velocity of 1000 m/s: at a range of 3000 meters.

It can be seen that the armour protection of the hull, turret platform, and turret significantly increased its shell resistance.

2. Armament installation

The gun in the modernized IS tank is mounted through the roof of the turret, for which a section of the roof is removed. The installation of a gun is simple and convenient. This method of mounting, as well as the placement of the sight in a special cast section of the turret, allowed the removal of immobile armour plates in the turret and, by removing mobile armour plates, shape the front of the turret to better resist shells.

3. Fighting compartment

The turret ring of the modernized IS tank is of the ball bearing type. A turret ring of this type provides for a freer spinning turret, and allows the removal of special turret grips, which increases the size of the fighting compartment.
The small commander's cupola with two MK-4 observation devices in the rotating hatch decrease the overall height of the tank and allow for 360 degree view for the commander.

In order to ease the opening of the hatch, a lightening device should be installed, like springs or torsion bars. The hatch should have a stopper to fix it in the open position.

An azimuth target indicator eases the commander's orientation and allows him to indicate targets.

4. Engine compartment

a) Fuel system

The fuel tanks in the modernized IS tank were moved to the engine compartment from the fighting compartment. This increased the size of the fighting compartment, and made the driver's job more comfortable. Additionally, the new fuel tanks have a reduced chance of catching fire if the tank is penetrated from the front. In place of the tanks, batteries were installed, increasing the amount of batteries from 2 to 4, which improves the electricity balance in the tank. The fuel tanks are interchangeable, which is rational in manufacture and convenient in use.

b) Cooling system

The cooling system for the diesel engine is the same as on the 701 object and Panther tank, and is located in the rear of the vehicle. Water radiators are placed near the air intake, which prevents them from being clogged with dust mixed with oil or diesel from the bottom of the engine compartment, which can occur in the production IS tank where they are near the exhaust.

The division of the air intakes between the engine system and cooling system is rational in the modernized tank, as the air taken in by the coolant system will be less polluted. It is desirable to transfer the filters from the engine compartment to the fighting compartment, which will make them easier to service and will partially aid in clearing the fighting compartment from gunpowder fumes.

In the production IS tank, the air sucked in by the fan is split into two streams, one of which cools the gearbox. On the modernized tank, the air does not cool the transmission, and overheating of the gearbox is possible, as evidenced by the trials of the partially modernized SPG at factory #100. It is necessary to modify a device (a vane wheel) to blow on the gearbox and keep the transmission temperature within acceptable bounds.

The fan case holder should be reinforced, as it could weaken, leading to a loosening of the primary drive to the fan and its breakage. 

The engine's temperature range is subject to mobility trials in the modernized tank.

5. Transmission

Main clutch

The main friction clutch of the modernized tank is reinforced. The levers have been placed inside the clutch, which made it more compact, and allowed the addition of one leading and one following disk, reinforcing it. The protection from dust is more reliable. The turning off mechanism has not been changed. As practice shows, the turning on mechanism is insufficiently protected from dust and must be improved. 

The base of the bronze cones should be increased to avoid rapid weakening of the main friction clutch on the end of the crankshaft. On the rear of the ring gear, mark a scale for the possible installation of gas distribution phases. Plan for the installation of a meter for counting divisions on the ring gear.

Chief of the 6th TU GBTU Department, Engineer-Colonel Solonin

Assistant of the Chief of the 6th TU GBTU Department, Engineer-Captain Bukatin"

CAMD RF 38-11355-2243

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! 

Combat Performance of 7.5 cm and 8.8 cm Guns

I've posted tons of very technical information on the performance of various 75 and 88 mm German guns. However, all that really doesn't say much about how well these guns performed on the battlefield. Thankfully, Colonel P.S Igumnov did all the hard work for me, and all I have to do is show figures from his doctoral thesis, "Investigation of Destruction of Domestic Tanks (using the experience of the Great Patriotic War).

Here's a nifty data set, distances of penetrations from the two aforementioned calibers:

And a nicer looking version of the data, compiled by fat-yankey. 

The data is not surprising at all. The majority of 88 mm hits are at 600-800 meters, exactly the range at which a Tiger would be engaging a T-34 according to the Tigerfibel. The mythical 2 km shots represent a negligible amount of the total. The 75 mm caliber favours closer engagements, at about 400-500 meters.

Axis Guns vs German Tanks

In order to determine if it is worth using a captured tank, it must be tested against other captured tanks. This article covers tests of German armour against guns used by the Wehrmacht and the armies of Axis minors.

In the 1942 report on trials of captured, domestic, and Lend-Lease vehicles (CAMD RF 38-11355-832), which you should all be familiar with by now, a number of such tests are described.

First, the LT vz 38, or PzKpfw 38(t), shoots at the StuG III.

At 100 meters, the 37 mm shell makes a 40 mm dent, but does not penetrate. At 50 mm, the formed is the same depth. Another shot from 50 meters, this time with an uncapped shell, makes a dent only 22 mm deep. Firing at the side from 850 meters, the Pz38(t) penetrates 3 times in a row. The diameter of the hole is 40 mm, which indicates ductile armour.

Subcaliber shells are loaded. From the same 850 meters, the shell hits a 10 mm screen, and breaks up. The main 30 mm armour plate has "an insignificant scratch" on it. Firing at the 30 mm armour with no screen, the shell fails to penetrate again. The core got stuck in the armour plate. Closing in to 400 meters, and firing at the screened armour, the shell only manages to make a 2 mm dent in the main armour plate.

The Pz38(t) starts firing at the front again. From 100, 200, and 400 meters, the subcaliber shell penetrates the front of the StuG. The diameters of the hole range from 15-18 mm.

Conclusions: "The 37 mm armour piercing shell does not penetrate the front 50 mm plate from any distance. The 37 mm armour piercing shell penetrates the side 30 mm plate from 850 meters. The subcaliber 37 mm shell penetrates the front from 400 meters. The subcaliber shell does not penetrate the 30 mm side armour."

Next is another captured and re-captured tank, the S35 Somua. Its 47 mm gun faces off against a StuG.

At 100 meters, it penetrates the front. Same at 250 meters. The diameter of the holes ranges from 45-55 mm. Another shot at 250 meters does not penetrate the front, but makes a 45 mm dent. Inside, an armour fragment equal to the shell caliber was knocked out. At 400 meters, the Somua penetrates once (next to the armour plate edge) and bounces off once, after making a 25 mm dent.

Conclusions: "The 47 mm AP shell penetrates the front from up to 300 meters."

Finally, we have two honest Germans facing off: a PzIII firing at a StuG.

At 100 meters, the shell penetrates. Hole diameter is 80 mm at the entrance, 60 mm at the exit. At 250 meters, the result is the same, with 50 mm on entrance, and 45 mm on exit. At 400 meters: 60 mm and 55 mm. Another shot from 400 meters penetrates the lower armour plate. At 700 meters, the shell penetrates the front of the StuG three times, with entrance diameters of 55 mm and exit diameters of 50-60 mm. At 800 meters, the shell penetrates the front plate, and gets stuck. An armour fragment 200 mm in diameter is knocked off on the inside

Conclusions: "The 50 mm armour piercing shell, fired from the 50 mm gun on the PzIII penetrates the 50 mm armour of a StuG at 800 meters."

In this test, you can also see that the StuG's ductile armour starts spalling once hit with a lot of kinetic energy, even if it doesn't crack like the Pz38(t) did previously.

That's it for the guns tested. The conclusions describe the shell condition after impact:
"The 37 mm German shell for the Czechoslovak 37 mm gun makes a 40 mm dent in a 50 mm armour plate at 50 meters. Without a ballistic cap, it makes a dent of 22 mm. Either way, the shell is fully destroyed.
...
The 47 mm German shell for the 47 mm French gun penetrates 50 mm of armour from 100 and 250 meters. The shell is not destroyed. The tip of the shell, in most cases, retains its shape.
...
The 50 mm German shell for the 50 mm German gun penetrates 50 mm of armour from 100 meters to 800 meters. The shell is not destroyed."

Next, let's take a look at the bigger German guns, fighting bigger German tanks. First up is the PaK 43, against a Tiger II.

"Shot #21. Target: upper front plate. Distance: 400 m. Dent 360 mm by 130 mm, 90 mm deep. A 510 mm by 160 mm fragment of armour was knocked out on the inside. A 1700 mm crack formed through the existing breaches.

Shot # 23. Target: front of the turret. Distance: 400 m. The shell hit the gun sight opening. Penetration, 130 mm by 110 mm entrance, 110 mm by 90 mm exit. 150 mm by 115 mm fragment is torn off the armour. The shell exploded behind the armour.

Shot #24. Target: front of the turret. Distance: 400 m. The shell struck the side of an existing breach. A hole was formed 100 mm in radius at the entrance. 270 mm by 220 mm, 130 mm thick, fragment of armour broke off on the inside. The welding seams on the gun mount ruptured, and the gun mount flew off.

Shot #25. Target: front of turret. Distance: 400 m. The shot made an entrance breach 140 mm by 170 mm, breaking off a 40 mm by 190 mm, 35 mm deep, fragment off the rear side. The rear of the turret has a hole 70 mm by 90 mm. The following welding seams burst: left turret side and turret rear, 600 mm in length, left turret side and turret roof, 950 mm in length, turret rear and turret roof, 450 mm in length, left side of the turret and turret roof (close to front), 500 mm in length, turret front and turret roof, 800 mm in length, turret front and left turret side, 200 mm in length."

Photo #26: The front of the turret penetrated by shots #23-25

Photo #27. The rear of the turret penetrated by shot #25.

"Shot #36. Target: lower front plate. Distance: 500 m. Shot hit an area damaged by shot #20. A breach 130 mm by 75 mm was found in a fragment of the hull that fell off."

The Tiger II's own gun (the KwK 43 was just a PaK 43 in a tank) seems to have trouble with the upper glacis, but spalling finishes the job, as always. The turret, however, is easily penetrated at 400 meters.

Next is the KwK 42, firing at the same Tiger II.

"Shots #26 and 27. Ricochet from the upper front plate into the turret.

Shot #28. Target: upper front plate. Distance: 100 m. The shot hit an area weakened by previous hits. A dent 280 mm by 110 mm was formed, 80 mm deep. As a result of cracks caused by previous shots, a 1500 by 1700 fragment of the hull fell off."

"Shot #29. Target: upper front plate. Distance: 100 m. Shell type: subcaliber. A 250 mm by 80 mm dent formed, 65 mm deep. Cracking from previous hits outlined a breach 730 mm by 600 mm."

Photo #29. Effect of a 75 mm subcaliber shell fired at 100 m.

Photo #30, indicating the section of the hull that fell off after shot #28. The ricochet from shot #29 is shown on the other side of the MG ball.

The Panther, despite its high velocity gun, cannot penetrate the front of a Tiger II, even after it has been weakened by numerous hits. Shots 26-29 do not even produce spalling, and half of them fail to do any damage at all, even to the perforated and cracked armour plate.

Penetration

If you read the World of Tanks forums, odds are you've seen this penetration table. Overlord even talked about it on his blog. For those unfamiliar with it, let me give you a quick translation. 

The column on the left is distance to target in meters. The first row lists the guns: "45 mm tank gun model 1938 on tank T-70", "57 mm gun ZiS-4 on tank T-34", "76 mm gun F-34 on tank T-34 and ZiS-3 on SU-76", "85 mm gun D-5 on SPG SU-85 and S-53 on tank T-34-85", "85 mm gun of increased power, experimental", "100 mm gun on SPG SU-100", "122 mm gun D-25 on tank IS and SPG ISU-122", "152 mm howitzer on SPG ISU-152" (ML-20), "122 mm gun of increased power OBM-50, experimental" (BL-9), "152 mm gun of increased power OBM-53, experimental" (BL-8, BL-10), "57 mm English gun" (6 pounder), "75 mm American gun on tank M3 Lee" (M2 tank gun), "50 mm gun Model 1938 on tank PzIII", "75 mm gun Model 1940 on tank PzIV", "75 mm gun Model 1942 on tank Panther", "88 mm gun on tank Tiger", "88 mm gun on SPG Ferdinand". 

The V0 value indicates the muzzle velocity of the shell. Under each gun name, there are two columns: one for an armour plate angled at 60 degrees from horizontal and one for an armour plate angled 90 degrees from horizontal. When two values are shown in one box, the numerator is the performance of a caliber AP shell, the denominator is the performance of a subcaliber AP shell. 

CAMD RF 81-12038-303

If you've seen it before, you also have heard criticism aimed its way. "Propaganda!" some people cry. "The 8.8L/71 penetrated 203 mm at 100 meters, not 168! This document is not to be trusted!"

They are wrong about the propaganda bit, as this was a classified internal document, used by engineers to analyze the required armour and firepower for future tanks. It would be pretty foolish to falsify these numbers. Besides, a dense table of data isn't exactly the best for propaganda material.

However, the 8.8L/71 did penetrate 203 mm of armour... when the Germans tested it. German penetration testing standards were different from the Soviets'. German penetration tests were performed with specially selected shells, against armour angled at 30 degrees. If a shell could penetrate the effective armour thickness 50% of the time (several times in a row, depending on the shell caliber), that penetration is recorded as how much that shell can penetrate.

Obviously, the Soviets didn't get courtesy shipments of special testing ammo, so they used whatever was captured along with German tanks. Therefore, these tests give a better indication of how a tank would perform on the battlefield. The Soviets had two penetration standards. When only one penetration value is shown, 75% of the shell fragments end up behind the armour plate. When two penetration values are shown, the two values are for 20% penetration (possible penetration) and 80% penetration (guaranteed penetration). So, as you can see, according to this data, while the 8.8L/71 could penetrate 203 mm of armour using special shells with 50% probability, it could only penetrate 168 mm using regular shells with 75% probability.

This document is very interesting, because it brings together most common guns of WWII (regrettably, some interesting ones are missing, like the 17 pounder or the Sherman's 76 mm gun) under the same testing conditions. This makes the comparison between the various guns much easier than having to pick through various sources, and then tring to figure out all the different test conditions.

Now, time to do some comparisons! You may have read a lot about the unprecedentedly devastating power of the Tiger's gun. However, it penetrates 120 mm at most. This is definitely high for WWII, but similar performance is reached by the Soviet 57mm ZiS-4, that was mounted on some T-34s since 1941, as well as the 85mm guns from the SU-85 and T-34-85. With APCR, even the ordinary T-34's 76 mm gun surpasses the Tiger in penetration (albeit at the expense of accuracy).

The Tiger's successor, the Tiger II, reaches better results with the 8.8L/71 gun, 168 mm. However, the D-25 gun on the IS-2 (which I compared to the 88 mm guns before) achieves nearly as much penetration, and the D-10T gun on the SU-100 (also tested on the T-34-85) surpasses it.

The Panther's long 75 mm gun also has very good penetration, and is comparable to the experimental 85 mm gun. Of course, the experimental OBM-50 and OBM-53 surpass all other guns on this table with huge penetrations of 230 mm and 244 mm, respectively. This would have been enough to take out a Maus tank, if Germany had ever sent any into battle.

In conclusion, the myth of superior German tank guns is, yet again, proven false.

See more penetration values in Penetration, part 2.