IS-2 - thickness of gun mantlet armor measured

[Amizaur]

Hello everyone!

I'm a long time fan of wargames focusing on armored warfare (Steel Panthers and CM series, mainly Eastern Front) and also tank sims like Steel Beasts and Steel Fury. I always appreciated high level of detail and accurate, realistic modeling of equipment (like optics) and physical events (like spotting, targeting, shooting, ballistics, armor penetration and post-penetration damage).

As time passes, games (some of them) become more and more realistic with help of much more armor & penetration data available today, than were not available 15 years ago. For example today we know that the mantlet of Tiger I tank is not uniform 100mm, which we believed 15 years ago. For years the 100mm was "official" because it was cited by reputable sources and authors.

Another example is the armor thickness of IS-2 front turret and mantlet armor. All information that is available is that it's 100mm thick and that idea of thickening front turret armor was considered, but was rejected because it would cause the turret to be unacceptably unbalanced.  But the turret is rounded and mantlet is not an uniform piece of steel. It's visibly thicker at center and thinner above and below, the new wide mantlet also had some area where mantlet armor and front turret armor were overlapped. Some sources claim 160mm thickness for IS-2 front turret armor. Some people wondered if the new wide mantlet was same thickness like old narrow one, or not ?

For years I observed people citing various sources (books) and debating which one is more reputable - I wondered why nobody just take a ruler, visit some museum or monument and just measure it to end the discussion ? For almost decade nobody did anything to satisfy my curiousity, so one day I decided to do it for myself. 

Fortunately, I live in Poland. There are some nice samples of war production IS-2 tanks in my country, some in museums, some others on monuments. The nearest one is in small town of Lebork some 80km from the place I live - model with new one-piece front hull armor and wide mantlet. So one sunny day I just took a ruler, a camera, and went to visit the beast to measure it personally and "just know". Measuring it was not so easy, some parts are hard to reach, some are unreachable from either outside or inside, it turned out that the data I gathered was not consistent/unambiguous so I visited it again few month later to do some additional measurements and check again some details of armor layout - it turned oout that you have to know the armor layout to measure some elements correctly. With additional data I finally knew the maximum thickness of mantlet armor and was able to reconstruct the armor layout of front turret and mantlet of IS-2. While visiting friends I had also an occasion to visit another IS-2 example,  model with an older two-piece front hull armor but same turret (wide mantlet) which is displayed as a monument in Nowa Huta (part of Krakow city). Measuremensts have shown that thickness of the mantlet is almost the same. The "almost" thing is probably effect of war production of crude cast armor elements.

Few years later I got my hands on simple but functional ultrasonic thickness gauge (OK, OK, I admit - bought it just for armor measuring :-)). So I visited both IS-2 tanks again to confirm my measurements with ultrasonic meter and to measure some armor elements I could not measure with a ruler. Using the meter on a rough surface of crude Russian castings - that were covered with many laters of old paint - turned out to be next to impossible. But after some effort I managed to find some small, smooth places stripped from paint where I got solid readings. There were no problems with measuring RHA plates - they were much more smooth, so finding good place was much easier. Using the ultrasonic thickness meter I could confirm thickness of front armor plates, side armor, side and rear turret armor, and of course front turret. I also confirmed my previous physical measurements of mantlet armor.

Now I could not only say how thick is armor in various places, but also reconstruct the armor layout of front turret and geometry of mantlet piece - it's theoretical geometry because the real one can differ up to +/-10mm from the "nominal" thickness. The casts are so raw and crude that such differences of  +/-10mm are quite normal when measuring for example thickness of cast front hull armor "plates" in various places. Talking about armor layout and geometry - there were some differences between tanks I measured and drawings I have found on the net. There were also some differences between those two tanks I measured. I guess it's the effect of war production realities - every factory did everything to simplify the production and did their own cast moulds, so tanks from different factories and different production batches varied in details, there were some improvements and some reductions and simplifications also. Details and dimensions that were not very important, were changed if that simplified production. So there are no absolute dimensions. There are only dimensions I measured on two pieces of IS-2 tanks, and using this data I tried to guess what were the dimensions of the original project designed by some intelligent and rational engineer at drawing board. Some big dimensions shown on my drawings are still not measured, for example the exact height of the mantlet piece. I didn't have such a big calliper to do that , the height is derived from other data but it may be not more than +/-10mm off.

Finally I satisfied my curiosity. And now while having such load of data, including ultrasonic measurements,  I thought that it may come in useful for others, so maybe I'll do some effort to put all this data together in nice graphical form and publish it on some wargamer's forums. I have also uploaded all photos I did while visiting those tanks, some of them documenting the measurements I did.

All results on my work are available for everyone in my public albums on flickr. 

https://www.flickr.com/photos/136792894@N05/albums

I hope this data will be used to improve armor modeling of IS-2 tanks in Combat Mission Red Thunder and also some other games I enjoy to play (for example War Thuner).

Here are links to flickr galleries with my work (drawings based on measuremensts). 

   Is-2 Tank - results of armor measurements    https://flic.kr/s/aHskrCY57j

and galleries with photos documenting my visits and measurements:

   IS-2 Tank, Poland, Lebork 1    https://flic.kr/s/aHskqLEAcw

   IS-2 Tank, Lebork 2, Poland        https://flic.kr/s/aHskrtkGkA

   IS-2 Tank, Poland, Lebork 3 (thickness gauge)    https://flic.kr/s/aHskq9HPoj

   IS-2 Tank, Poland, Lebork 4 (thickness gauge 2)    https://flic.kr/s/aHskqWLgQy

   IS-2 Tank, Poland, Krakow/Nowa Huta 1    https://flic.kr/s/aHskntK6iX

   IS-2 Tank, Poland, Krakow/Nowa Huta 2 (thickness gauge)    https://flic.kr/s/aHskqPsCB6

 

Ih shorts, the results are:

- the turret armor of IS-2 tank (model with wide mantlet) is 100mm all around. There are some differences due to crude castings, actual thickness vary from 90 to 100mm, with most of turret being 100mm. The armor of rounded parts (mainly front turret left and right of mantlet) becomes thinner up and down, where the angle increases. My drawing of front turret armor profile is approximate, I measured troughly only the front curved parts.

- the turret armor in area of the gunsight port is thinner, about 80mm thick, but it's covered by 75-80mm thick part of mantlet armor. So armoring of this area is really 75...78mm of mantlet armor + 10-20mm of air + ~80mm of turret armor.

- max nominal thickness of gun mantlet armor was 115mm in both tanks I measured. Mantlet in one tank was a bit "reinforced" in area around MG port and there up to 120mm thickness was measured, but the "original" shape would be 115mm. The mantlet is tapered up and down, becomes thinner where angle to vertical increases. I believe I reproduced the actual geometry of the cast moulds, being two cylinders 660mm in diameter, separated by 115mm (maybe they ment 110mm or 120mm in original plans, but on both tanks I measured it was 115mm). Such "model" when drawn, fits almost exactly to the measured mantlet profile.

- the left part of mantlet covering the gunsight port is only 75 to 80mm thick. It may be up to 80mm thick at center and 75-77mm thick at height of gunsight hole. The actual measurements were from 74mm to 77mm at the height of gunsight hole, depending on place of measurement and tank. The IS-2 from Nowa Huta/Krakow was 75mm, the Is-2m from Lebork was closer to 80mm.  So again, thickness of that part of armor is combination of 75mm of matlet + 80mm of turret armor.

- The most thick part of mantlet is about 130mm above the gun and gunsight axis. In other words, the gun is mounted slightly below the thickest part of the mantlet.

- the thickness of other parts of armor (the hull) is in accordance with known data.  For the older hull, the upper front is 120mm cast, the slanted part 60-70mm thick, lower front hull 100mm thick cast, sides 90mm.  The newer hull with single piece nose - upper front 100mm thick cast (NOT 120mm), lower front 100mm, the front-side parts of upper hull up to 135mm thick and gradually becoming thinner on their way back, to 90 or 100mm (I forgot to check) where they are welded to the rear 90mm RHA plates. Lower side hull 90mm. So I can confirm that IS-2m upper front hull plate is 100mm thick for cast front-hulls. So probably it's made from 90mm plates in RHA-made front hulls. Other thing I can confirm is that front-side belts of IS-2m upper hull are thicker than 90mm, they are up to 130mm thick. Unfortunately I didn't check them for older-hull IS-2 model from Krakow. Will do that on occasion.

I wonder if I can attach some pictures here... let's try...

 

 

Hi there...

Regards,

Amizaur

 

P.S. If someday I get my hands on IS-2 tank with narrow mantlet, I'll check it too. I wonder it it's the same.

 

Edited December 26, 2015 by Amizaur

[Bud Backer]

Wow, that's some lovely detailed work and diagrams! Nicely done.

 

[ChrisND]

After the eggnog wears off and the coffee kicks in, I will dig into this lovely post.

[Jotte]

This is an absolute treat to read.  Thank you for the time and effort you've put into this.

[Battlefront.com]

Indeed!  Thanks for the detailed post.  It's a rare post that I send to Charles to make sure he reads.  This is one of them

Steve

[kevinkin]

Thank you for the post. Very nice. I had a mentor early in my career who said "this has to be knowable, go find out". He would have loved your analysis.

Kevin

[Migo441]

This is awesome!  Get this man a Europass; there are plenty of monuments to measure.

[76mm]

hmmm, there wouldn't happen to be any King Tigers near your town, would there?

[akd]

good job sir!

[Amizaur]

Nope, no King Tigers in Poland at all... but... IIRC there is a front turret plate from KT (dug-out part of blowed up tank) somwhere in Poland. Stripped of the zimmerit, easy to measure. Seen pictures of it somwhere on the Web. 

Got it. 

 

http://www.strefacichego.pl/?module=museums&id=73

What do we need to know about KT front turret ?

 

P.S. I just checked that this museum with KT front turret is located at Skarzysko Kamienna town which... I'm just passing trough about twice a year when traveling from Gdansk in north Poland to Krakow on the south, visiting my family there. Lot's of good stuff laying there in grass, so I'm definitely going to do a short stop while traveling this route next time

Edited December 27, 2015 by Amizaur

[Vanir Ausf B]

Awesome work, Amizaur!

The front turret plate of a King Tiger would be a great follow-up. It was officially 180mm but measured thickness is reportedly in the 185-190mm range.

 

[slysniper]

I think you just earned your title as a official Armor Grog.

That was a real amount of effort you put in there.

I have used the ultrasonic thickness gauge for work to get readings on old building and pressure vessel steel.

But I would think you had a real challenge to get it to read for you at all. looking at the shape of that steel you were looking at.

Especially the interior with how the steel is rusting and scaling could make for poor output.

 

Anyway, impressive.

just buying a ultrasonic thickness gauge shows what kind of a grog nerd you are. Them things are not cheap. 

[MarkEzra]

Others seem shocked at the lengths you've gone,but not me. After all...you are a Steel Panthers and CM fan!  Thank you. Your efforts are greatly appreciated by wargamers everywhere.

[RockinHarry]

Now that is armor grog field works par excellence! Thumbs up, Amizaur! 

[Bulletpoint]

Impressive work. 

[c3k]

LOL! The best part was this: "Few years later I got my hands on simple but functional ultrasonic thickness gauge (OK, OK, I admit - bought it just for armor measuring :-)). "

The second best part was realizing someone else was taking the pictures while you were holding the device. THAT person (wife?) deserves a medal. Or a dinner out.

This deserves honorable mention somewhere, and a free game. Or two.

Ken

[Migo441]

The second best part was realizing someone else was taking the pictures while you were holding the device. THAT person (wife?) deserves a medal. Or a dinner out.

Definitely.  I mean look, those of us who obsess about CM and hang out on the forums are a little daft and we expect it in each other.  It makes a certain amount of "sense" that you'd take a sophisticated measuring instrument and visit WWII era tanks.

But the fact that another human being went with you...  Willingly!?  That's where it gets strange!  

[spawncaptain]

Are you the Amizaur who has also made the LWAMI mod for the sim "Dangerous Waters"?  

Edited December 27, 2015 by spawncaptain

[Amizaur]

Thank you very much for your kind words. Thank you  for kind words. I`m really glad that my works are pleasing for someone :-).

That second person on pictures is my future wife

Fortunately, there is only one Amizaur nick in the world :). The nick came into being somwhere in late 90's because I used an Amiga computer then (and still have it somehere) and was proud member of it's community (I'm still today). It turned out to be quite unique, so it stayed... :).Yes, I was working on improving improve Dangerous Waters sim, but it was long ago :). I also did a small mod aimed at increasing realism of tank part of Red Orchestra game. My interests and hobbies includephysics, science and history. I also like to test and work-out game mechanics of sim games (and find bugs) so they can be improved. ;P. Have to admit that working out game mechanics takes out the whole fun from the game itself (when you know how everything works under the hood, that there is no magic there), but I just can't resist not to test and check things... ;). Long ago I played CMBB a lot, but in CMRT I did probably 10x more testing than actual playing "for fun"... same was in Dangerous Waters back then. And that is sad, because that probably means that I'm either too old or too curious, inquisitive and questioning to actually enjoy games...

Cheers ! 

P.S. In those new albums I have uploaded everything related to IS-2 (pictures, schemes, photos) that I found on the net and used to better understand the subject. 

https://flic.kr/s/aHskrDhzc2

https://flic.kr/s/aHskohNasS

https://flic.kr/s/aHskohNRQf

https://flic.kr/s/aHskqMzuo8

https://flic.kr/s/aHskrDnJFT

https://flic.kr/s/aHskrLj7Bs

 

Edited December 27, 2015 by Amizaur

[spawncaptain]

Yes, I was working on improving improve Dangerous Waters sim, but it was long ago.

Guess there aren't too many simmers out there! The LWAMI team did nothing short of fixing the game, making it several times more enjoyable. No need to be so humble.

[Amizaur]

Original DW was unplayable for me :), fortunately there were many ways to improve things - modyfiing not only the parameters in database, but the scripts that decided how every platform in game (ship, sub, missile, torpedo) behaves, moves, "thinks". So we could design new more inteligent and more realistic scripts, that made weapons behave like real ones (their physics, logic, sensors) and make enemy ships smarter, also to correct many bugs in original scripts and even to find workarounds for some bugs in game engine (untill they were fixed) or do some things (like handling ship damage) in our scripts instead of being done by the main game engine. It was a good game, after all, because it allowed those modifications :). 

Edited December 28, 2015 by Amizaur

[c3k]

 

 

 

(Hmm...I "quoted" erroneously, somehow...)  Looking at the above image, I am curious about the profile view on the right. The thickness seems to be measured to the center of the mantlet (the black line). Yet, the same numbers are used in the center figure for the thicknesses on the right edge (as viewed).  I think the mantlet gets thinner towards the top and the edges, and perhaps the image is just a "generic" image. Is that correct?

 

 

 

 

 

Edited December 28, 2015 by c3k

[Amizaur]

The matlet is made from two parts. The central one is similar to the old "narrow" mantlet - up to 115mm thick, gets thinner toward top and bottom. The right (on the picture) "added" part that covers optics area is 40mm thinner (so up to 75mm), also gets thinner up and down. Check the horizontal mantlet cross-section on another picture. Also check those two albums on flickr

https://flic.kr/s/aHskohNRQf

https://flic.kr/s/aHskqMzuo8

There are pictures of IS-2 tank front turret without mantlet, the thinner "around optics" area is clearly visible there, it helps to understand the shape of the mantlet.

Edited December 28, 2015 by Amizaur

[c3k]

Thanks!

[Amizaur]

Some interesting photos and drawings (repost from another forum, because pictures are worth to be shown here):

Below is armor diagram of IS-1 tank with 85mm gun and basically the same narrow type mantlet as IS-2 mod 1943. You can see that opening in armor is almost same size as the mantlet width. There is only a small 20mm wide and 40mm thick ledge of front turret armor that overlaps with 115mm of mantlet armor.

(if narrow mantlet was also 115mm too, I can't know that untill I find one and check it). A shell hitting the joint of mantlet and turret would penetrate much more easily, going along this slit. BTW, on this picture the thickness of the narrow mantlet looks identical to front turret thickness so 100mm. But I'm not sure how detailed and precise this drawing is. It's from tank manual, showing how the gun is mounted, not a technical factory drawing.

Here is diagram of Is-2 turret armor with wide mantlet. It's almost identical, it differes by the left main part of mantlet (lower part on this picture) being a little wider and a 75mm thick extension  added to it that covers thinner (80mm) part of front turret armor with optics port (area marked as 26 on the picture). But the main thick part of mantlet overlaps with turret armor still only by 2cm wide and 4cm thick gig of turret armor. 

 

BTW, mantlet was mounted to the main gun on a rubber shock absorber (labeled 28). 

 

In another album (called "IS-2 tank photos - today", or something like that) there are some photos of IS-2 tank with it's gun mantlet removed - dimensions of the opening in front turret can be seen there - it's barely covered by this sheet metal cover.

 

Compare those two photos:

 

 

on above photo the part on the right (with oval/vertical opening for telescopic gunsight) is 80mm thick.

 

On picture below, it's covered by a 75mm thick mantlet  extension (of trapezoidal shape), added to the main, thick part of the mantlet 

 

 

 

Below is top view of upper turret. Look at those lines on armor above (below on the picture) the mantlet - they help to locate.

(Compare this with the model photo below.)

 

Those two vertical lines visible on armor that are closest to the center are NOT where the opening in the turret armor is.

Opeing is only about 2cm from the edge of the main mantlet part. 

 

 

This is how opening looks like, unfortunately only in model, but it is done accurately:

 

 

And here, looking closely under the mantlet, you can see the edge of the opening in front turret. As you see it's  just like in the model photo above, opening is almost as wide ans the main part of the mantlet:

 

 

Interesting thing to notice on above photo - the armor under the mantlet is only about 40-50mm thick, because it's almost horizontal and normally also shielded by lower mantlet. But if an armor piercing projectile hit top of upper front plate or even skidded from the turret ring protector and was deflected slightly upwards, it would hit exactly there with almost full energy, probably penetrating the thin cast armor there and entering turret under the gun. Especially in late tanks with 60deg upper plate I see this as a shot trap.

Detonation of 88mm HE shell in this space (between top hull and turret, under the mantlet) would probably remove the turret from it's mounting and possibly kill the driver by splinters from the top armor above his head... 

Vertical cross sections:

IS-1:

IS-2:

(unfortunately the turret armor is not shown here - and it's worth to note that the front part of turret armor (the bolted-in, rounded part) is different for  Is-2 than for IS-1. In IS-2 it's longer because the gun pivoting axis is moved further forward. So the drawing of IS-1 front turret armor can not be used to understand how Is-2 front turret armor looks. Only the main turret part (central and rear one) is identical. The front "bolted" part is different.

 

Edited December 30, 2015 by Amizaur