New information regarding IS-2 Armor (extensive research)

[MikeyD]

An interesting bit on that Russian Battlefield link I had posted above. There are sectional drawings of four different IS-2 bow types. Though the figures give both the cast and welded late bows 120mm, the drawings themselves 'eyeball' closer to 100mm and 90mm, respectively! It looks like the author was following his sources instead of the evidence of his own eyes!

[rexford]

Originally posted by MikeyD:

An interesting bit on that Russian Battlefield link I had posted above. There are sectional drawings of four different IS-2 bow types. Though the figures give both the cast and welded late bows 120mm, the drawings themselves 'eyeball' closer to 100mm and 90mm, respectively! It looks like the author was following his sources instead of the evidence of his own eyes!

It is interesting, and a good observation.

Here are the Russian Battlefield statements that form the basis for mantlet strengthening:

"As for the tank's turret, it turned out to be impossible to increase its armour protection. Designed for the 85 mm gun, it was completely balanced. After installing the 122 mm weapon, the turret became very unbalanced. The Design Requirements intended for an increase of its frontal armour thickness to 130 mm which would have unbalanced the turret even further and would have made a new traverse mechanism necessary. SInce all these changes required a complete redesign of the turret, they were all cancelled."

Increasing the turret front to 130mm is not feasible due to weight problems and turret unbalancing.

It looks like the turret weight was not increased, which means that the unbalance problem was not solved.

"Nevertheless, the appearance of the turret was considerably changed in the process of its production. The first batch of tanks manufactured in 1943 had a narrow porthole through which the sighting telescope fits. After the installation of the D-25T Main Gun, it became almost impossible to use the telescopic sight, even though its breech was the same as that of the D-5T."

Yes, the turret would appear different with a 122mm gun and the widened mantlet.

"Starting in May of 1944, a new turret with a widened porthole was manufactured, which resulted in the sight being moved to the left. The armour protection of the tank's mantlet was improved and the armour thickness of the sides of the lower hull was increased."

Have not been able to find any data that confirms the statement about the thicker lower hull side, it looks like 90mm on all IS-2 tanks.

Now here's the greater contradiction:

the turret front armor could not be increased because the added weight would be a problem, but the widened mantlet, which covers a fairly large area compared to the turret front, could have thicker armor and weigh more.

One can't have it both ways: if the turret front armor cannot be increased in weight the mantlet also can't increased.

However, and this may be the key, a wider mantlet would offer better penetration resistance since edge effects would be reduced. With the narrow mantlet many hits are going to be close to the edge where ballistic resistance is compromised and reduced.

With the wider mantlet, most mantlet hits will be far enough from the mantlet edge to have minimal or no reduction in armor resistance.

So widening the mantlet improves the resistance to hits even if the thickness remains the same. That may be the meaning of the mantlet armor improvement statement.

[ August 09, 2003, 03:44 AM: Message edited by: rexford ]

[rexford]

Originally posted by MikeyD:

An interesting bit on that Russian Battlefield link I had posted above. There are sectional drawings of four different IS-2 bow types. Though the figures give both the cast and welded late bows 120mm, the drawings themselves 'eyeball' closer to 100mm and 90mm, respectively! It looks like the author was following his sources instead of the evidence of his own eyes!

If one compares the IS-1 and late model IS-2 armor drawings on the Russian Battlefield site (see last figures on page at http://www.battlefield.ru/is2_1.html), the IS-1 and late model IS-2 have the same turret front and mantlet thicknesses.

The lower hull side thicknesses are also 90mm for both IS-1 and IS-2, which contradicts the statement that the lower hull side armor was increased for late model IS-2 tanks.

But the side superstructure thickness in the last drawings is 90mm on IS-1 and 100mm on IS-2, so the Russian Battlefield article on IS tank development is referring to the wrong armor area! Another case where the drawings conflict with the text.

[ August 09, 2003, 03:40 AM: Message edited by: rexford ]

[Denizen]

Now here's the greater contradiction:

the turret front armor could not be increased because the added weight would be a problem, but the widened mantlet, which covers a fairly large area compared to the turret front, could have thicker armor and weigh more.

One can't have it both ways: if the turret front armor cannot be increased in weight the mantlet also can't increased.

Yes and no; it all depends on where the weight of the gun is balanced. The weight of the mantlet is not carried by the front of the turret in the same manner as the turret armor itself, rather the mantlet's weight is genrally balaced as part of the gun with which it moves. *If* the fulcrum of the gun is futher back into the turret than the front face of the turret itself, an increase in mantlet weight will affect the whole turret balance less than than the same weight increase of armor on the turret front. Granted, it will affect the balance of the gun, but this can be counteracted by the weight and shape of the interior gun assmebly. Thus it is not necessarily true to say an increase in mantlet weight and turret weight are one in the same in terms of balance.

In other words, the gun acts as a lever inside the turret, and as the mantlet rests on the gun, it is part of that lever. The impact of more total weight on the level will only affect the turret balance at the fulcrum on the lever. So if the fulcrum moves back, the overweight balance on the front of the turret is relieved at least partially, and adding a bit more weight to the lever at the mantlet and a balanced amount on the inside might only bring the complete turret balance up it is former figure, even though the mantlet is now heavier.

There is, furthermore, evidence that a movement of the fulcrum to the furthest rear position perimissable may have taken place. The visible weld seam that connects the main turret assembly to the gun mounting moved backward when the change was made to the wide mantlet, even thougth the turret front extened out as far as in the early version.

[ August 09, 2003, 04:32 AM: Message edited by: Denizen ]

[Denizen]

As for the information presented in the drawings on battlefield.ru the following must be said:

The drawings are not works of the people behind that website, however the numbers on them, are. Several of those exact drawings appear in their original form in some of the Russian books I used as sources for this debate, however, the numbers represented on them in the books are different. IF you look closy at the armor profile of the IS-2, you will see two different fonts used on the numbers. The italisized numbers are those in the book, the others are not. Incidentally, the book which has the IS-2 profile uses it to represent *every* model of the IS-2, I have yet to see a version-specific diagram of the entire tank.

The writing on that site is genrally quite accurate, but the diagrams they present often aren't worth the bandwidth they use up.

[ August 09, 2003, 05:13 AM: Message edited by: Denizen ]

[rexford]

Now here's a bit that might explain references to more than 110mm for IS-2 Model 1944 mantlet thickness.

Page 34 in our book shows a detailed drawing of the Panther G mantlet, with a cross section. While the nominal thickness is 100mm, the trunnion pad area is 125mm to 135mm thick and the area at the left and right edges is 90mm.

So 160mm may be a relatively small and ballistically inconsequential trunnion pad area, while the vast majority of the area is 110mm.

[rexford]

Originally posted by Denizen:

As for the information presented in the drawings on battlefield.ru the following must be said:

The drawings are not works of the people behind that website, however the numbers on them, are. Several of those exact drawings appear in their original form in some of the Russian books I used as sources for this debate, however, the numbers represented on them in the books are different. IF you look closy at the armor profile of the IS-2, you will see two different fonts used on the numbers. The italisized numbers are those in the book, the others are not. Incidentally, the book which has the IS-2 profile uses it to represent *every* model of the IS-2, I have yet to see a version-specific diagram of the entire tank.

The writing on that site is genrally quite accurate, but the diagrams they present often aren't worth the bandwidth they use up.

You say the drawings are the same as those you found in other Russian references which you have used during your research. Well, the drawings show the thicknesses on the turret front and mantlet remaining the same from IS-1 to IS-2 model 1944.

Unless the mantlet numbers (thickness) presented in the books are different, I would say that the reference books disprove the mantlet thickening theory.

[rexford]

Originally posted by Denizen:

</font><blockquote>quote:</font><hr />Now here's the greater contradiction:

the turret front armor could not be increased because the added weight would be a problem, but the widened mantlet, which covers a fairly large area compared to the turret front, could have thicker armor and weigh more.

One can't have it both ways: if the turret front armor cannot be increased in weight the mantlet also can't increased.

Yes and no; it all depends on where the weight of the gun is balanced. The weight of the mantlet is not carried by the front of the turret in the same manner as the turret armor itself, rather the mantlet's weight is genrally balaced as part of the gun with which it moves. </font>

[rexford]

The following will show that the IS-2 turret was always unbalanced by the 122mm gun throughout the war, which placed limits on the thickness of the turret front and mantlet armor.

First off, the M10 provides some interesting insights into turret balance.

The 3" gun unbalanced the turret, so weights were added to the rear turret overhang. Unbalance in the front is remedied by adding weight to the rear, which makes sense and is consistent with the physics of the situation. Too much on one side requires that more be added to the other side.

The IS-1 turret was designed for the 85mm gun, and was balanced. The IS-1 turret armor is 100mm on the sides and rear.

The early IS-2 turret became unbalanced because the weight of the 122mm gun put too much weight up front compared to the rest of the turret. The early IS-2 turret had 100mm side and rear armor, same as the IS-1.

Now, all of the materials I have reviewed regarding the layout of the late model IS-2 turret show 100mm side and rear armor on the turret, same as the early IS-2.

So, if the early model IS-2 turret was unbalanced, so was the late model IS-2 turret.

And if the mantlet thickness on the late model IS-2 was increased above the early IS-2, it would add to the unbalance by throwing even more weight towards the turret front (the mantlet weight is shifted towards the front of the turret through the connections).

To all of the above I would add that the Russian Battlefield site states that a 130mm turret front armor was ruled out because it would require a new turret traverse to rotate the heavier turret.

Well, if 30mm more turret front armor could not be added because it would overstress the traverse mechanism, that would appear to rule out the following:

1. no way the mantlet weight could be increased by a significant amount (like a 60mm increase to 160mm)

2. no way that weights could be placed in the rear of the IS-2 turret to counter the weight of the gun and bring the turret back into balance (have never seen or heard of weight being added to the turret rear of that tank)

3. no way that the turret side and rear armor could be increased by enough to counter the unbalancing created by the 122mm gun

In summary, there are MANY facts and statements that totally rule out the theory that the IS-2 turret suddenly became balanced, allowing the mantlet to be thickened substantially.

It would be good if evidence could be presented that disputes the above analysis.

A brief summary of the facts that support balancing of the turret, and a thicker mantlet, would help here.

[ August 09, 2003, 10:47 AM: Message edited by: rexford ]

[rexford]

Following statement from http://www.battlefield.ru/is2_1.html

"After installing the 122 mm weapon, the turret became very unbalanced. The Design Requirements intended for an increase of its frontal armour thickness to 130 mm which would have unbalanced the turret even further and would have made a new traverse mechanism necessary. SInce all these changes required a complete redesign of the turret, they were all cancelled."

The above statement from the Russian Battlefield site appears to rule out design changes (other than the wider mantlet) to the IS-2 turret shape and thicknesses between the IS-2 early and late war models.

Which would have maintained the same turret unbalance throughout the WW II life of IS-2 tanks, unless giant weights were hung in the turret rear, which would have required a new turret traverse mechanism (which was not installed).

[ August 09, 2003, 11:04 AM: Message edited by: rexford ]