Is IS-2 early's front turret that vulnerable?

[melm]

Hi, I have a real question on IS-2 early model's front turret armor. While I was playing Soviet Campaign, I found that IS-2 early model's front turret is very easy to be penetrate by Stug III(I lost three due to front turret penertration). However, Stug III almost unable to penetrate IS-2's side turret. According to my humble and limited knowledge, I think there is something wrong here. As long as I know, IS-2's front turret shall have 100mm armor and side turret is 90mm. From the decal I see, the hit is exactly on the front turret  and nowhere near mantlet.  If I am wrong anywhere, please correct me. Thanks.

[Vanir Ausf B]

The Stug's 75mm cannon will penetrate 100mm of armor out to about 1300 meters.

[melm]

The Stug's 75mm cannon will penetrate 100mm of armor out to about 1300 meters.

But why it can't penetrate 90mm side turret armor?

[Vanir Ausf B]

I think it's because the IS-2 benefits from the center of mass aiming when side-on to a shooter. When viewed in profile the turret is positioned so far forward on the hull that the center of the hull is directly below the portion of the turret where the side curves around towards the rear. The vast majority of hits are on this rear/side turret transition area rather than square-on. This means the impacts are hitting at a highly oblique angle.

I will make a mental note to bring up the issue with BFC to double check the side turret thickness and see if anything can be done about the shot placement.

[JasonC]

Sorry, melm is right here and the depiction of JS turret vulnerability is kind of ridiculous in CM.  It already was in CMBB, still is in CMRT for the early model ISs.  The late ones are fine.  The issue is the way the game handles "round" armor - it gives it a high probability of a flat hit with no slope effect to speak of.

In real life, the Russians used IS tanks as breakthrough fighters because they could approach dug in antitank guns like PAK 40s frontally, and shell them from medium range, with impunity.  Stronger armor on the turret was only needed to handle threats like Panthers and up.  Vanilla long 75 German AFVs were greatly outranged, and with the towed version the tank could pick the range (normally, some keyhole and terrain exceptions of course).

In CM, only the "late" IS-2s have those characteristics.  I've run even number duels between Panzer IVs and IS-2s earlier model and the Panzer IVs are favored.  Which is completely ridiculous.  Of course the IS-2 gun is sufficient against the Panzer IVs armor, but it has a very low ROF.  The IVs get ranging shots then follow ons faster, and easily find not only the turret, but flat hits on the turret that kill IS-2s.  In reality, the place where the slope is least is almost all covered by extra mantlet thickness, and the majority of the surface with "only" 100mm of armor has significant slope.

A Panther should be favored in that sort of duel, until the late model IS-2s appear.  But that even paper thin Panzer IVs with 75L48 guns are better tanks than early IS-2s in tank vs tank fighting is something only CM has ever suggested, and historically is just not remotely credible.

Edited January 12, 2016 by JasonC

[Vanir Ausf B]

In reality, the place where the slope is least is almost all covered by extra mantlet thickness, and the majority of the surface with "only" 100mm of armor has significant slope.

Images courtesy of Amizaur.

[Amizaur]

For early Is-2 with narrow mantlet there is almost no overlapping mantlet + turret armor. There is either 100mm (max) of front turret armor OR 100...115mm (max) of mantlet armor.

 

Here is IS-1 turret armo - the IS-2 with narrow mantlet would have  almost identical layout, only the separate frontal would be little longer, because the  big 122mm gun had to be mounted little more forward (pivoting point moved ahead of the joint):

 

The wide mantlet is max 115mm thick (120mm in some reinforced areas), the narrow mantlet was either the same (115mm) or only 100mm thick. I had no occasion to measure narrow one yet.

P.S. I wonder why Russians after testing Is-2 mod 1943 against KwK36 reported that the front turret cannot be penetrated, when upper hull could be penetrated up to 600m, lower hull up to 1400m, sides of turret (100mm cast) up to 2500m o even more. Sides and rear of turret is 100mm thick all around, the bolted-in front turret casting is same thickenss. Maybe they were made of different hardness or material ? Or maybe the spherical shape made them some percent more resistant than a flat plate (in the same way as architectonic arcs works?) Or it's just a bogus info, because at the same time they called for front turret armor reinforcement to 130mm (which could not be done because of turret unbalance as we know). 

In theory the central flat areas of front turrret should not be more resistant than flat areas of side turret (or even slightly less because side turret is always little sloped in vertical).

Are there any reports (German?) about Is-2 front turret penetration distances by various guns ? I mean combat reports or ballistic tests, not calculated ones...?

Edited January 14, 2016 by Amizaur

[JasonC]

Amizauer - I've looked for actual battle loss reports and there are quite a few from the Russian side, on causes of battlefield losses of IS-1s and early IS-2s.  

A full company of Panthers from ambush at 700 meters - 5 dead IS-1s.

Tiger I hits to the lower front hull.  Tiger I hits from the side at medium range (1000-1100 meters).

Tiger front hits multiple times at 1500-1800 yards, no damage.  Then from the flank at 500 meters, KOed and brewed up.

StuG ambush from the flank, engine compartment hit from the side, brews up.

Multiple cases of Tiger I hits and kills.

3 IS-1s lost to an 88 Flak battery at medium range.  Plates hit not specified.

2 IS-2 earlys hit by a "battery" (who knows what that really means?) of PAK40 at 150-200 meters.  8 hits on 1, 4 hits on the other, both knocked out.

More StuG engagements with all frontal hits ineffective, followed by side hits up to 800 meters that KO, including another engine compartment hit with fire.  Another hits the turret ring but does not penetrate, after which another side hit at 500 meters KOed the IS-2.

A Tiger I that bounces shots off the nose at 800 meters, then get a front-side hit that penetrates and kills.

Frontal kills by 75L48 in the reports I've found, only the 200 meter PAK battery *maybe* (angle not actually specified, number of hits is).  

75L48 kills from the side are confirmed.

Some frontal kills by 88L56 are confirmed but appear alongside bounces at 1500 meters or more, and specifically nose armor bounces closer than that.

Plenty of 88L56 side hit kills confirmed.

Panther hits and kills from the front confirmed, routine.

Kills at 1 km plus by 75L48 from the frontal aspect - nowhere to be found.

Absence of evidence is not by itself evidence of absence, but when it appears with that many reports of tanks killed by common weapons, it would at least be strange to see none by the most common German weapon type from the most common battle orientation.  And there *are* 75L48 reports in the set, they just always kill from the side, or at 200 meters in one case.  Nobody is reporting the turret front as an especially vulnerable spot.

Make of it what you will.

Edited January 15, 2016 by JasonC

[JasonC]

To be a bit more systematic than my last, and not go from memory...

Verified Russian side confirmed battlefield losses of JS-1s and early JS-2s with reported causes -

JS-1s

Losses to Panthers, 5 tanks at medium range.
Losses to 88 Flak, 2 tanks at medium range.
Single loss to a Tiger I at 1500-1800 meters, plate hit not specified.
Two lost to Tiger Is under 1000 meters, from ambush.
Two lost to a PAK-40 battery at 150-200 meters, 4 and 8 hits respectively.

JS-2s 

5 StuG hits to front armor at 1500-2000 meters - no damage.
1 StuG hit to flank from 600-700 meters - knocked out.
Tiger I hit at 1000-1100 meters to lower front hull - KO.
3 Tiger I hits to nose armor at 1000-1500 - no damage.
1 Tiger I hit to front-side armor from 400-500 meters - KO.
Tiger I hit at 400 meters to front hull armor.  Penetrated, but recovered and repaired.
88 Flak to side from 500 meters into engine compartment, KOed.
Tiger I hit flank at 800-1000 meters, KOed.
Two side hits, caliber and range unspecified, KOed.
Turret hit plus engine side hit, caliber and range unspec, KOed.
StuG ambush at 800-1000 meters.  First, turret ring hit no penetration.
Second, engine compartment hit, knocked out.

 

[ASL Veteran]

So Jason, would you be able to provide links to the original reports that you obtained that information from?  If they are not located online perhaps you could at least cite the source so others can look at the information themselves?  After all, I don't think that you were personally inspecting knocked out JS tanks on the battlefields of WW2 so I have to assume that your memory is referring to a memory of some document or book of some kind and not memories of personal experience.   Amizaur is demonstrating where his information and data comes from and he explains his methods such that others can repeat or confirm what he has done.  You aren't participating in a way that is similar since you are just providing uncorroborated information from sources that are unknown.  This discounts your contributions to this thread because there is no basis from which someone can judge how relevant or accurate your information is.

[Amizaur]

ASL Veteran - Jason reputation as person with good knowledge about WW2 tanks is just good as cited source :). This data can be found without problem on the net (russian battefield site I guess) if you need it.

I admit that I have also noticed strange lack of evidence for front turret penetrations of IS tanks. There are very few photos of such penetrations (I have counted 2 or 3) and not much combat reports. Either IS front turret was - in practice - stronger that it theoretically should be...

Or just IS tanks, after the initial suprise and some partially-succesfull front-attack attempts, were rarely (if at all) enagged from the front, German tanks maneuvered to engage from the side (untill long 88mm guns appeared). 

Front vunerable areas were small (some flat front turret areas and big front lower plate - the upper plate was not that vunerable and was quite small anyway) so in frontal enagements at over 500m many shots or much luck was needed to even hit there. Target possible to kill, but really hard, so decision to avoid frontal engagements was optimal.

And  - as the above Jason data shows - IS-2 from side aspect is easy (big and not especially hard to penetrate at any point) target, can be knocked out even by Stugs from +1000m.

So maybe just the vunerable front turret areas were small, not many shots fired in initial engagements actually hit there, and later frontal engagements were in general avoided, side-shots were preffered. 

Personally I can consider the front turret armor being 10...20% more resistant than it "should" - because of it's spherical shape or high hardness steel or something like that. But not more. The spherical sides left and right of mantlet are just 100mm thick, I inspected them from outside and inside.

The mantlet is not more than 115- 120mm thick at thickest part (few centimeters above the gun axis). The area directly around the gun is about 200mm but it's very small "ring" of armor wrapped around the gun tube.

Mantlet was mounted to the gun tube sleeve with 4 big screws, on a rubber shock-absorbing pads (I guess that "floating" mouting on amortising pad could increase mantlet resistance by one or few percents).

The front turret should not be more resistant than 90...120mm of RHA (depending on T/D ratio and accounting for hard casting) and mantlet not more than 100..140mm (as above). And even those higher numbers are definitely within reach of KwK36 under 1000m. 

Areas close to mantlet edge (both edge of mantlet and edge of turret opening for gun) should suffer from free edge effects and provide protection less than 100mm.

 

P.S. I just found some info suggesting that mantlets of early IS-1 (IS-2?) was made from bent 100mm RHA slab. But I didn't see any photo of any IS with RHA mantlet. Maybe is was info about some prototype or project. All IS-2 mantlets are definitely cast pieces. It's much easier to produce. 

I'm still wondering why the mantlet is 115mm thick, when front turret only 100mm thick. Why 115 ? 100mm of RHA when  "corrected" to be made with cast armor of the same resistance would give about 115mm. But it's probably wrong theory. The mantlet design thickness may be not 115mm but  110mm or 120mm as well, and the measured number is just inaccuracy of poor casting process. On all large cast parts there are differences in thickness (measured in various points) up to +/- 10mm.

On the other hand, do not believe that the design thickness of the mantlet could be 100mm and the measured 115mm caused by such large casting/mould inaccuracy. That would be too big error even for Russian war production realies. +/-5mm for mantlet are plausible (just as +/-10mm for large, more expensive parts like front hull). +15mm for small part like mantlet is too much, such mantlet would be scrapped I think.

 

 

Edited January 15, 2016 by Amizaur

[ASL Veteran]

ASL Veteran - Jason reputation as person with good knowledge about WW2 tanks is just good as cited source :). This data can be found without problem on the net (russian battefield site I guess) if you need it.

 

 

I don't really care about the topic one way or another.  However, knowing a person's sources when making statements or claims is helpful and is generally accepted as a good principle to follow when having an honest discussion.  I don't know how many books Jason has published or how many technical papers he has authored, but if you are comfortable with Jason's 'expertise' as an accepted 'original source' on a subject then that's your choice of course.  I should note that even published authors do list their bibliography and source material.  Published works are typically footnoted so it is not like asking for a simple citation is an overbearing or unusual request.  Nobody credible relies upon reputation alone.  Individuals who do research of original documents and publish aren't hesitant to cite the sources of their information since citing sources serves to bolster their credibility not detract from it.

[Amizaur]

I've seen this data somwhere on the net, and I trust Jason citied it correctly. That is all I need personally now. I don't write any historical thesis at the moment :). Some of it is probably from here: http://english.battlefield.ru/tanks/10-heavy-tanks/19-js-2.html and if not, better sources are listed at bottom of the page, like "Studying the JS tanks being destroyed in summer-autumn 1944", NII-48, Sverdlovsk, 1945;

Edited January 16, 2016 by Amizaur

[JasonC]

Amizauer is right (big surprise ?) - it is on the net, at the English translation version of Russian Battlefield, citing original Russian unit loss reports that where evaluated when deciding to uparmor the later models of the IS-2.

Meanwhile, back on planet earth, there is scant real world evidence of 75L48 routinely KOing IS-2s from the front at over 1000 meters.  But I have long since - lietrally years ago - reported test fights in which Panzer IVs beat even numbers of early IS-2s in CM.  My standing advice in the matter - also literally years old but I'll reiterate it here, since this thread's IP noted the same issue and asked - is to use the late IS-2s exclusively, if you want historical levels of performance for the beasties.  Works fine, those are modeled well, no issues remain using this solution.

Edited January 16, 2016 by JasonC

[Amizaur]

Is it modeling of hull or turret that makes such big difference between early and late IS-2 in CM? 

[Amizaur]

Interesting photo, never seen it before:

 

Both photos definitely show the same tank - the captured "Kummersdorf" example. The right one with markings of armor thickness&angles is well known.

The left seems to show the same tank just after it was knocked out. There are visible penetrating and non penetrating hits on the armor which are labelled with range and weapon. Another possibility is some kind of test range against German guns, but the first (after battle report) seems more likely. 

The lower front hull seems to have one or two non penetrating hits labeled "1200m Tiger"  (or at least this is what I can read). Non penetrating probably because they were almost "glancing" hits, the shells deflected to the left and the front armor was supported by the side plate.

On the upper front plate is a mark labeled probably "1200m Tiger" or "1000m Tiger". Maybe it's a trace done by glancing hit to the highly-sloped glacis plate (visible on the right photo froom above) which deflected and had to end on the upper front plate. Or maybe it's some small calibre weapon ? Well, it's definitly labeled "Tiger". Or maybe the label is to some other mark in shadowed place (like turret ring below mantlet) where a shell hit ?

Finally, the front turret has a clear penetration labeled... anyone can read it ? I can even see if the range label has "1" + 3 digits + "m" like "1200m" or only 3 round digits like "800m". Would be interesting to know the range and weapon for sure. Anyone seen a better copy of this photo ?

 

 

Edited March 10, 2016 by Amizaur

[Vanir Ausf B]

I can't say for sure, but all 3 hits look like "1200m Tiger" to me. 

[Amizaur]

Quite possible, I thought about this too. It could be just single engagement from 1200m, with Tiger commander adjusting the range up after seeing first two shots hitting  low and not penetrating. Third shot hit higher, the sloped front plate, ineffective. Range adjusted again (or aimpoint shifted) up, fourth hit front turret, the end.  At range of 1200m each adjustment of gunsight by +100m would move hit point up by about 1.1-1.2m. 

Shots came slightly from the left which is visible by the bounce mark on the glacis. Gunner aiming center of mass - or aiming the ground level below center of mass and adjusting range to hit higher (as in Tigefiblel). All hits are pretty lined into a vertical line. KwK36 is pretty accurate at 1200m. Look at those two at the bottom. Almost to the same place.

Edited March 10, 2016 by Amizaur

[Amizaur]

I got some new info about "Kummersdorf" IS-2 and it's penetrations. Seems it was not a single, 1200m enagement:

"This IS-2 Mod 43 was captured in May 1944 during fighting, it was arguably the first inspection of the new tank. Before, German intel noted rumors from prisoniers "Gefangenenausagen", that it would have 250mm armor.

However, the Report (Gen.Insp.d.Pz.Tr., NB #12, June 1944) claims it was taken out of action by a "Nashorn" at the turret front, from 2600m.

 

a) LFP: penetrated by Tiger I, from 1200 m

b. UFP: dent and several cracks, no penetration. Tiger I fired from 1500m

c) Front hull spike, left, was penetrated by Tiger I, 800 m.

d) Report suggest a penetration of the DFP at under 500 m,  LFP from 1000 meters, turret front and side from 3000m.

"

Turret from 3000m would be possible for Nashorn, not KwK36 . 

[MikeyD]

One additional thing, I don't know if BFC is taking into consideration is the quality of the armor castings. If Charles is rating early IS-2 armor as 'low quality' (or however he scores it) then 100mm turret front would less impressive than it appears by the number. It would be interesting to learn if early production IS-2s and IS-85s were allotted crap cast armor compared to the later war vehicles. I recall one email from Charles he was pegging Hetzer bow armor quality as 'mediocre' and the side armor as 'low'. I believe he said that he was even typing in the Brinell hardness numbers! So there's more going on under the hood than we can guess at.

[Vergeltungswaffe]

Item eleventy million and five on the wish list would be the ability to set the armor quality in the editor.  From what I've read, Soviet armor quality for most of 44 was probably worse than we think and German was better, being then quite reversed by 45.

[Amizaur]

Even bad quality hard armor can resist well if struck by projectile which has calibre smaller than thickness of armor. On the other hand, it would fail badly when attacked by projectile larger than it's thickness.  So IS-2 hard, cast armor of 90...120mm thickness could protect well from 75mm, not bad from 88mm shells, but would be much more vunerable to anything larger (like 128mm guns that are popular in some other games  ).  Panther gun have better penetration pefrormance from Tiger I gun, but Russians after testing found that ranges at which IS-2 is vunerable are lower ranges for Panther than for Tiger. 75mm vs almost 90mm of calibre. 

One thing that would be always bad, against any calibre are defects, cracks, voids in cast armor and non-uniform thickness. IS-2 castings could be full of such defects. An any tank would be really a bit different. One vehicle could be made from good, other made from bad castings.

I was always for some kind of "randomising" armor quality for tanks in games (one would be little different than other, you could never be sure at what range you can penetrate it - like in real life), or even for every plate of every tank (rather easy with today's computers - randomise parameters of each tank armor by certain amount during initialisation of the game scenario).

Edited March 12, 2016 by Amizaur

[Michael Emrys]

I was always for some kind of "randomising" armor quality for tanks in games (one would be little different than other, you could never be sure at what range you can penetrate it - like in real life), or even for every plate of every tank (rather easy with today's computers - randomise parameters of each tank armor by certain amount during initialisation of the game scenario).

Sounds good to me. Thumbs up.

Michael

[Amizaur]

Someone in another forum posted two interesting photos of IS-2 after being captured by Germans and loaded onto a train. There are much more holes in this tank, from different ranges. Maybe they did some kind of test-shooting the wreck, before they decided to transport it to Germany.

and two good quality drawings of IS-2 mod 1944 armor:

I did some measurements on the last blueprint. They may not be worth too much, the scale and proportions of the picture may not be preserved well, but anyway I was interested in results.

It's clearly visible that both front lower and upper plate of model 1944 had the same thickness (90 or 100mm). The mantlet seems a bit more thick than front hull plates. 

The visible dimension of the barrel (4475mm from the end to gun pivoting point) is 751 pixels long on my picture. So one pixel = about 5,96mm (+/- 0,01mm). The mantlet thickness seems to be little less than 19 pixels, but more than 18 pixels. 18 pixels = 107mm, 19 pixels =113mm. I would estimate mantlet thickness for 18.5 pixels and this would be about 110mm. That would be designed thickness.

The LOS thickness of upper front plate seem to be close to 30 pixels, that's 179mm. The plate is angled at 60deg, so we have to divide by two  to get armor plate thickness, we get 89,5mm. So this is drawing of UTZM version of front hull made from 90mm RHA plates.

If on the upper drawing we assume the shells mounted in the rear of the turret are 122mm in diameter (31 pixels), then the thicnkess of the mantlet (28 pixels) would be 110,19mm. Again 110mm. And the mantlet profile seems to be designed in such a way, that it's LOS thickness in any point of it's curvature is equal to 28 pixels (so 110mm). The angle increases, the LOS thickness remains the same.

 I would assume for now, that the design thickness of the mantlet was 110mm, and the measured 115mm was due to inaccuracy in casting process.

 

 

Edited March 13, 2016 by Amizaur

[Amizaur]

The drawings that I linked in the post above are NOT drawings of actual production model of IS-2 mod 1944. Those are drawings of an "IS-2 mod 45" prototype. 

I just cleared this up (the description of the drawings I got was an auto-translation from Russian to English and at first it was not clear for me what model of IS-2 is on drawings).

The description was:

Drawing relates to the further improvement of the tank JS-2 mod44. Its main feature was to reduce the frontal area of the projection due to the fact that an instrument is removed through the roof. They were transferred to the fuel tanks in the engine compartment, the new cooling system, the engine capacity of 600 hp, the new cooling system (the type of tank Object 701 and Panther) and many other changes.

This project was completed in August, the tank was built by the fall of 1944 and tested, because of the many changes in the technical part of proevilis some flaws. over which did not work, simply turning the project.no photographs on the tank did not survive (there Kirov Plant Museum, which was why it was liquidated in the Soviet era, and then apparently had lost all photographs, but there is a test report. Work on the implementation of the next innovations in IP-2 most likely due to the fact that in parallel there was a work on the tanks JS-4, JS-6, JS-3/

At first I didn't notice much difference in this drawings from ordinary IS-2 mod 1944 so was not sure what is on the first and second blueprints.

But after superimposing them one on another and comparing with drawings of IS-2 mod 43 and 44 I noticed that those two pictures are parts of the same blueprint, and noticed the differences from production IS-2 models. 

Different is the front part of the mantlet (the housing of the gun tube), whole front part of the turret was redesigned, the TSh-17 gunsight was moved to the rear (probably the horizontal turret profile is more narrow and curved, much different from IS-2), the turret roof plate is redesigned, ventilation opening moved to the rear ect.). But the vertical profile of the front turret and mantlet (at least in the center part, close to the gun axis) is identical as in Is-2, mantlet thickness on this drawing is also same as for IS-2 (about 110mm).

So, it's an interesting drawing of IS-2 mod 1945 prototype :). And it's hull is like IS-2 mod 1944 (there are internal mods but armor is the same).

Second comment from the author:

No, lined drawing does not apply to JS-2-44, This drawing of the tank which I wrote, significantly improved version JS-2, As I mentioned to him applied the new tower, the figure can be seen just above the embedded drawing of the tower separately. Forehead body on this tank is identical to the tank JS-2-44. 

on the reservation tank guns masks JS-2 towers and gun accordingly masks were made in four different factories, in my opinion this is the main reason that the same tank cannon defense of 110 mm and the other 115 on the factory drawing gun to protect the maximum thickness does not reflect, although if measured with a ruler on the drawing, taking the measure of the length of any of the segments is known, the maximum thickness of just the same varies in the range 112-115 mm, but these all toschiny the drawing should not be taken seriously.in reality head-on parts JS-2 especially far from the figures, what you yourself have seen, for example obstrelenny at the site in July 1944 spryamlёnny molded body had a thickness of 130 mm front part.

I would like to add at distances of defeat is given in the document above, the distance obtained by calculation or so: shelled object was placed on the guns at a distance of 100 meters, and further various distances simulated lifting powder, so that the actual lesion distance could be less or more.

Edited March 15, 2016 by Amizaur