Sunday 3 November 2013

Improving the IS-2

The IS-2 model 1943 (at this point, still indexed IS-122) was a fearsome opponent for enemy tanks, infantry, and fortifications alike. However, there was still room for improvement. The following document outlines some proposed changes to the tank.

"Measures to increase the combat ability of the IS-122 tank

1. Turret and hull

1. A hull whose strength matches the armament may only be reached by replacing the clearly obsolete shape of the upper front plate. The front of the IS-122 must be shaped like the front of the T-34, with a 120 mm rolled armour plate (figure #11) within the limits of the tank's dimensions (figure #12).

Figure #11. Parallel cross-section of the front of the IS-122 tank hull. 

Figure #12. Front of the altered IS tank hull. 

The necessity of producing this type of front hull is confirmed by penetration tests of the front plates of the Panther tank with the German 88 mm gun from the Ferdinand SPG. The upper front plate of the Panther tank, 85 mm thick and sloped at 55 degrees, could be penetrated with armour piercing shells at 600 meters. The altered front of the IS-122 tank hull will be impenetrable by armour piecing shells from the 88 mm gun (Ferdinand SPG) at any distance.

The front of the turret should be 200 mm thick, turret sides 150 mm thick. 

2. Increase in fuel storage, ammunition capacity, and crew comfort may be reached by increasing the width of the hull within the dimensions of the tank (figure #13). 

Figure #13. Perpendicular cross-section of the IS-122 tank hull.

Due to obvious advantages of rolled armour over cast, the upper hull should be produced with rolled armour. By placing the sides at 45 degrees (instead of the current 15), the thickness of the plates could be reduced to 75 mm.

2. Armament

1. Due to the outlines disadvantages of the 122 mm gun (two-piece ammunition, screw breech), it is necessary to replace it with a smaller caliber gun of equivalent power (preferably 100 mm). "

- CAMD RF 38-11355-2369

A lot of these features were implemented in the model 1944 modernization, but not all. For example, the 100 mm gun projects never really got anywhere. Instead, the gun was equipped with a superior semi-automatic sliding breech, but kept the two-part ammunition.  

One-part ammunition was definitely attempted.

CAMD RF 81-12038-697

"To the Chief of the GAU KA, Marshall of Artillery, comrade Yakovlev

Regarding the letter from GAU KA from May 12th, 1945 on the topic of order 940670ss, I report that as a result of GOKO decision #6863ss on November 4th, 1944, NKV factory #9 developed an experimental 122 mm D-25 gun that uses one-piece munitions, and sent it to the Kirov factory on May 21st, 1945, in order to be mounted in the IS tank

D. Ustinov"

I don't envy whoever had to serve as the loader on that experimental tank. 122 mm ammunition is rather large.

T-44, first variant, with 122 mm gun, demonstrating the dimensions of the shell.

Here are models of the existing IS-122 (center) and proposed hulls, surrounding it. Neither was used, but the right one inspired the IS-6 hull shape.

As for the ammunition storage on the IS, here is an attempt to increase it.

CAMD RF 38-11355-2606

The diagram is a bit convoluted, but it makes a lot more sense with the labels:

"Diagram #2. Placement of 122 mm ammunition in the IS-122 tank.
  1. Thirteen armour piercing tracer shells in the turret bay.
  2. Fifteen high explosive fragmentation grenades in the turret bay.
  3. Three additional shells affixed with belts to the lids on the ammunition crates.
  4. Twenty six propellant casings in the fighting compartment, and two on the side of the turret.
  5. An additional placement of three casings with propellant placed as follows: one on the lid of the left ammunition crate, one in the front left corner of the hull, one in the right hull bay."


  1. So one piece 120 mm highly angled plate was never implemented?

    1. It was implemented, along with other front hull improvements, on the model 1944. The rest didn't make it through or was implemented later for post-war model.

  2. I was going to ask the same questions. There were several series of IS-2 obr 1944, with different front glacis protection:

    - Cast steel: 110-100mm, some early on with 120mm?
    - Rolled steel: 90mm.

    All Russian sources I have to state a 120mm protection, but V. Fofanov stated that this was an error repeated in most sources

  3. Any info on a pike-nosed IS-2?

  4. I'm asking because 120mm@60 is like 240 effective armor. That thing is more armored than IS-6

    1. I'm quite confused too with what was actual frontal hull thickness of the IS-2. Alejandro for example has been through a discussion about this and found one IS-2 to have a frontal armor of 100 mm instead of 120 mm. It might be because of different factory producing models with different armor thickness/type though.

      Still, you can shoot the weaker turret and lower hull armor, they are not particularly strong.

  5. So the lower front hull of the model 1944 is only 75mm thick?

    1. Keep in mind that not all improvements were implemented. I believe the only part that was implemented to be the upper front hull.

  6. I'd be curious in knowing if there was a difference in armor thickness between the IS-1's small mantlet (also used in the early versions of the IS, or IS-122) and the larger mantlet of the IS-2 model 1944. You see printed values of 100 mm, 110 mm, and 160 mm.

    I have various books, including Baryatinsky's, but nothing really makes sense. We read that a Panther tank needed to close within 600 m to take out an IS-2, yet the same books then claim that a Tiger I tank (whose 88/L56 gun was considerably inferior to the Panther's 75/L70) could do knock out an IS-2 at 1,000 m, even maybe upwards of 1500 m). It makes me wonder if we're talking about two different armoring schemes--that maybe the reference to the Tiger I involves the IS-1 and early version IS-122s, while the reference to the Panther involves the IS-2 model 1944. Just on the face of these references, a gun mantlet armor of 110 mm for the IS-1 and early IS-2/IS-122 versions would match almost precisely the cited armor resistance to the Tiger I's gun, while a mantlet thickness of 160 mm, combined with the changes made to the hull armor for the IS-2 model 1944, would match almost precisely the cited resistance to the Panther's gun.

    Steven Zaloga has published a picture of a knocked-out IS-2 model 1944, tank #441 of the 7th Guards tank brigade. The turret of this tank was secreted by to the US for inspection by the US army. I have written the National Archives about the report that was written but they didn't find it.

    But, the picture tank #441 in Zaloga's book shows that its mantlet has been blown off the turret front by an internal explosion and is resting midway down the gun barrel. I have blown up the photo and, using published data on the dimensions of the IS-2 to create a scale, attempted to measure the mantlet's thickness (the attachment which bolts the mantlet to the internal gun cradle has been blown even further down the gun barrel and does not interfere).

    What I see in the photos is that the mantlet's thickness is not uniform. It is thinner at the edges and thickens around the gun barrel. When I measure the edges, it's about 110 mm thick using my crude scale. But around the gun barrel, it nearly doubles in thickness.

    1. I have also tried to contact the National Archives about that IS-2. There was a guy in tank-net who claimed to have the report, but he never gave any details on the report title. You can find the original discussion here:

      Steve Zaloga has mentioned the IS-2 evacuated to the US in several articles (Military modelling February 2008). The best option would be to contact him to see if he could provide a reference.

  7. A guy climbed up and measured the mantlet of the model 1944 in Czech museum Lesany. The wide side was 120mm and the small side was 80mm thick.

  8. The IS-2 mantlet is not uniform in thickness, I measured it personally from outside and inside, was unable to reconastruct a whole picture but at least some parts are measurable. It's definitely not 160mm, maybe in part close to the gun... Additionaly an internal turret armor 40-60mm thick lays under the part of external mantlet armor which are 100...120mm. Maybe the sum of those two (120+40=160) was cited as 160mm. The layout of mantlet and turret armor is somewhat similar to the T-34/85 turret scheme, which was developed later and has improved shape. I'll try to dig out my notes and schemes I didn some years ago when visiting an IS-2 monument in Lebork. Poland.

  9. I found a photo of an IS-2 mod 1944 in Berlin penetrated on its mantlet, the entire gun housing/turret front came off from the turret. The turret roof is also seams missing and the gun breach is pointing out.
    link to the photo/site:

  10. There seem to be no difference in mantlet thickness from early narrow version to late wide version. Seems that it was widened only. But I'll check that if I have chance to visit some narrow mantlet IS-2.

  11. I measured the IS-2 wide mantlet and front turret again, from outside and inside, I also got some readings with an ultrasonic thickness gauge, but the surface was too rough (and covered with many layers of flaking paint) to measure the turret troughly. The front turret is up to 100mm thick. The mantlet is up to 120mm thick (left and right of the gun, but it is tapered when going up or down, so 120mm is only in very central part, 10cm higher is 110mm, a bit higher is 100mm and so on, same when going down from the center. The right part of the wide mantlet (where the gunsight is) 80mm thick, backed up by 80mm of front turret armor. The side turret armor of the IS-2m in Lebork / Poland is 100mm thick, rear turret the same. The turret armor is just 100mm all around. Mantlet is a bit thicker, as I described above. Upper front hull is 100mm thick casting (60deg), lower front hull is 100mm thick too (30deg).