Thursday, 1 November 2018

D-10 in the IS-2

"To the Commander of the Motorized and Mechanized Forces of the Red Army, Marshal of the Armoured Forces, comrade Ya.N. Fedorenko

Having examined the results of comparative trials of the 122 mm D-25 gun and 100 mm D-10 gun, the Red Army GAU concludes that:
  1. The rate of fire of the D-10 gun is up to three times higher than that of the D-25 gun, which is a significant advantage of the D-10 gun.
    The 100 mm D-10 gun presently has an insufficiently robust armour piercing shell, which does not guarantee reliable penetration of the Panther's armour at a range of over 1200 meters.
    The decision to install the 100 mm D-10 gun on the IS tank should be delayed until the armour piercing shell and semi-automatic mechanism of the D-10 gun are perfected.
    Since the 100 mm D-10 gun and its ammunition in its existing form are already significantly more powerful than the 85 mm D-5 gun, it is necessary to rearm the SU-85 SPG with the 100 mm D-10 gun, for which a pilot batch of SPGs with the D-10 gun should be produced with corrections of drawbacks of the gun and SPG that were revealed during trials.
  2. The 122 mm D-25 gun reliably penetrates the front armour of the Panther tank from a range of over 2000 meters.
    The armour piercing shell of this gun is sufficiently robust, and the HE grenade has a sufficient explosion and fragmentation effect.
    Until the ammunition and components of the D-10 gun are perfected, the 122 mm D-25 gun must remain as the main armament of the IS tank.
Conducting experiments with the creation of a 122 mm single piece round is reasonable, but you must consider that the use of a single piece round will require a change to the chamber, sunk part of the shell, and the casing.

The mass and dimensions of a unified 122 mm round will make the loader's job more difficult, which will definitely not increase the rate of fire of the D-25 to the level of the D-10.

Regardless of the result of comparative trials of the D-10 and D-25 guns, the installation of the S-34 gun in a tank and an SPG will continue. 

Commander of Artillery of the Red Army, Chief Marshal of Artillery, Voronov
Marshal of Artillery, Yakovlev
April 20th, 1944"

CAMD RF 38-11369-490 pp. 35-38


  1. Another interesting document for me! An occasion, I put interesting citation (I found this citation in earlier article about "D-10 vs D-25" comparision, originally citated by Stewart Millen):

    "The report explains this with the lower muzzle velocity of the D-25T: at such a large range, the heavy 25 kg shell has no problem penetrating the Panther's front, while its higher arc lets it impact the front of the Panther at a favourable angle. The D-10T's shells are faster, and therefore fly flatter."

    This is interesting, because some time ago, I'm interested about theory "bigger distans mean bigger angle of impact, and less sens of angled armour- if we discuss about armour angled like upper front plate of Panther/T-34/Sherman, not about armour angled like glacis of BMP-1/Abrams tank". And I found that even on pretty big distans, angle of impact it's small. I found that on 2000 meters projectile fired from D-25T 122mm gun (typical AP projectile) have 1.2 degree angle of impact. BTW, I found that for D-25T gun, point blank range (3 meter tall target, BR-471 projectile) was 1130 meters- im my opinion good enought for typical tank fight.

    1. I believe your assertion about the heavier shell coming in at a higher angle thus hitting the sloped armor flatly is correct. But in this case I suspect the Soviets thought of the JS tanks as breakthrough tanks and was even more concerned with the D-25T's increased blast effect against fortifications as opposed to tanks. And to be fair the D-10's higher velocity has a much shorter time of flight to target greatly enhances chances of getting a hit.
      As it was the T-54/55 100mm D-10 gun tanks accompanied the JS-3 through T-10 122mm D-25 tanks for many years.

    2. I think that you don't understand me- in my opinion that's NOT true that slower and heavier projectile mean significally smaller efectivness of sloped armour (glacis of Panther or similar angled armour). In my opinion 1.2 degree angle of impact at 2000 meters it's extremly small angle of impact.

    3. AKMS. AS I understand it a large slow projectile will come plunging down when fired at longer ranges, which ironically makes slopped armor less effective. Tank my word for it. 2000 yards is a long shot for WW-2 tanks. When engagement shots are made at that ranges the simple act of tank drivers to jink the tanks to the left and right can cause shots to miss after they are fired. Now I can not testify for WW-2 tanks what counts as point blank range, but I saw a deer shot at 1140 meters with a dummy training round in 1982. Strangely enough the deer at Ft Knox had gotten used to sounds of gunfire or something, and just walked across the firing range. But in real life tanks are moving and often the gunner is hurried.

  2. AKMS,

    The citation I gave was from report from the Chief of Experimental Machinery to the Chairman of the Technical Council. I think you are probably right about the report's reasoning about the relative angles upon impact of the two guns as the cause of this being wrong. However, I think the report was correct in its assessment that the D25-T did have in reality superior armor penetration against most targets than did the D-10. The reason, I believe, was not in the ever-so-slightly-less angle of impact, but because of possible drag effects and the differences in the degree of overmatching.

    To whit, at 0 degrees, using the US Army definition of penetration, the penetration values of both guns (uncapped APHE rounds in use most of 1944, mm of armor):


    D-25 196 mm
    D-10 208 mm

    500 m

    D-25 179 mm
    D-10 188 mm

    1000 m

    D-25 158 mm
    D-10 164 mm

    1500 m

    D-25 141 mm
    D-10 144 mm

    2000 m

    D-25 125 mm
    D-10 126 mm

    You can see, actually by 1500 meters, the two guns are essentially equivalent, certainly at 2000 meters. I don't know why, for two uncapped APHE rounds, but I suspect drag is a big reason.

    Now let's assume shooting at the front of a Panther, at zero degrees. Let's neglect the nearly flat small areas of the turret (100 mm) and the lower hull (60 mm @ 55 degrees) which are easier targets for both guns but are hard to hit. The bulk of the front of the target is either going to be the rounded 100 mm mantlet (let's assume an average slope factor of that to be 1.5) and the 80 mm thick upper hull (at 55 degrees, this has a slope factor of 2.1).

    However, the real resistance to the incoming round would have to take into effect the relative overmatching of the two guns. The Panther's armor resistance differs between the two. The equation is:

    Effective thickness = (1 + [(nominal slope enhancement-1) x (raw thickness/round diameter)])

    For the 100 mm D-10 gun, the Panther calculates to have the following effective thicknesses:

    Gun mantlet: 150 mm
    Upper Hull: 150 mm

    For the 122 mm D-25 gun, I get:

    Gun mantlet: 141 mm
    Upper Hull: 138 mm

    Now, this calculation doesn't predict what the Chief of Experimental Machinery contended in his report (it's less optimistic than what he contended, maybe because by October 1944 the effects of ever-degrading German armor was manifest?) but does predict that even though the D-25 has less nominal penetration, it will defeat the front of a Panther at longer ranges than the D-10 (at 1500 m the D-25 still penetrates, while the D-10 does not).

    1. I agree with you- I know than large caliber projectile can have a worse vertical armour peneration and better sloped armour penetration- sloped armour have a biggest efectivness if enemy projectile don't have bigger diameter than armour thickness (real thickness, not line of sight). But i wrote about a angle of impact- I think that on typical combat ranges, it don't be important.

    2. Isn't it basically simply that heavier projectiles retain their energy better by sheer inertia over long distances? Projectile mass, after all, remains quite unchanged while velocity goes down from drag and other Usual Suspects of aerodynamics ergo the performance of the lighter shell relying more on its velocity for kinetic energy degrades faster. AFAIK that's one of the major reasons why in small arms the larger calibers are used for long-range shooting, too.

    3. That's what I always thought, Kellomies, but just looking at penetration dropoffs it's had to make comparisons (maybe because of round differences). Here a postwar British report does show the Kwk43's performance dropping off considerably compared to say, the German 128:

      My point of posting this, however, was just to challenge the usual narrative about putting the 100 mm D-10 on the IS-2. Usually said narrative goes 'it was a good idea but the production of the 100 mm gun and ammo weren't adequate, and there was a loss of HE capability versus soft targets, etc."

      That all may be true, but the fact is, that for all potential German armored targets that the IS-2 might face save maybe the Tiger II and Jagdtiger (in short, for something like 99 % of what the IS-2 would likely face, period), the 122 mm D-25 actually had superior anti-armor performance as well, mostly because of overmatching. And even with the Tiger II (not sure IS-2s ever met any Jagdtigers) the D-25 was capable enough.

      So there was really not much of any rationale to go to the D-10; it offered few advantages. With an automatic loader, the rate of fire for the D-10 mm was faster (but with the problem of smoke buildup in the tank's interior); without it, it's marginal. The ergonomics with the IS-2 is better with the D-10 but the IS-2 already had pretty good ergonomics to begin with. The ammunition supply increase (anywhere from 28, to 29 rounds to 35 depending on the configuration) isn't a game-changer either. So all in all, I think the Russians did the reasonable thing--to keep the D-25 in the IS series, and focus on creating a superior anti-armor round for it.

      To me, if I were going to rate the biggest improvement opportunity for Soviet armored hardware in the 1944-45 period, it would not have involved the IS-2 at all, but focus on improving the T-34/85's increasingly weak hull armor, which was superb by 1941 standards but had not been thickened since inception and now was overmatched by most gun calibers it would face. Something like the T-44 (80 mm hull, 120 mm turret) would have made a big difference, making the T-34 almost invulnerable to Pak40 fire frontally and eliminating the Panther's range advantage (i.e., the Panther could only take out such an uparmored T-34 frontally at close ranges it would itself be vulnerable to, frontally). That would have likely saved a lot of tanks and a lot of lives.

    4. Stewart Miller I agree with keeping the JS-2 but not for the same reasons. It was really the best heavy tank of the war. The improved JS-3 must of been a claustrophobic nightmare. And I suspect they wanted to get something like the T-44 going before the end of the war. And from what I read everybody was surprised that the transverse engine caused very few problems. Though one would think that some time in the next 50 years someone would develop a improved transmission for T-44/54/55s.

  3. "at 0 degrees, using the US Army definition of penetration, the penetration values of both guns."

    "1000 m
    D-25 158 mm
    D-10 164 mm"

    Where do these numbers come from? Are these algorithm generated numbers? AFAIK the US didn't produce any foreign gun firing tables. The foreign gun tables they did possess were either made by the British (who used a 20/50 criteria which was different than the 50/50 US criteria) or, translated foreign tables using the original criteria.

    1. I snagged them off the War Thunder Wiki, which agrees with most published sources where it can be checked. It appears War Thunder got most of their data from Bird and Livingston, WW2 Armor and Gunnery ; the values for these guns match that source. I don't think you could nit-pick them much further; all such data are averaged data that contains a significant spread.

      I have seen tables supposedly concocted from Aberdeen data, but they may be extrapolations of British data. I do have the report of the British 1946 testing now.

    2. Somebody is messing with them over there and Wikipedia. It is not from Armor and Ballistics as I have both editions and it is different. Also, the ballistic capped and ogive shell penetrations are too closely matched. If you can find the DDR 122mm tables you'll see the difference.

      This is a translation of some Russian firing tables.

      They match the penetration values found on the Russian Battlefield site.

    3. I found downloaded Armor and Ballistics from Scribus

      I don't think anyone can monkey around with what appears to be a scanned copy. The Russian data is on page 59, and lists the same figures that War Thunder uses for the two guns above (both with the non-capped APHE rounds). Not to mention these aren't the only places similar data is found.

      I took look at your link, and it says on page 3 that "these tables are a translation of the original Soviet firing tables, however these tables have not been checked by the United States Army Ordinance Corps Firing Tests". Ergo, they're Russian data, using the Russian 80 % certified penetration data and not (as Bird and Livingston) recalculated to US/British standards for purposes of comparison. The data you linked to is essentially identical to the table that Peter posted here:

      Where the Kwk43 penetrates 168 mm of armor at 100 meters, zero degrees, instead of 232 nm.

  4. Like I said the numbers at the War Thunder wiki is not the same as Armor and Ballistics.
    A&B MV=3000f/s Wiki=895m/s /2936 f/s
    Wiki 100mm APHE 1000m 164mm 2000m 126
    A&B 100mm AP 1000m 157mm 2000m 119
    Wiki 100mm APBC 1000m 167mm 2000m 128
    A&B 100mm APBC 1000m 185mm 2000m 141

    This is the A-19 or D-25 gun not the D-25T tank gun.
    A&B MV=2600f/s Wiki=795m/s /2608 f/s
    Wiki 122mm APHE 1000m 158mm 2000m 125
    A&B 122mm AP 1000m 149mm 2000m 112
    Wiki 122mm APBC 1000m 162mm 2000m 129
    A&B 122mm APBC 1000m 162mm 2000m 129

    The only match is the A-19 122mm APBC BR-471B which is not even covered by this article.

    As to the KwK43 on that table. The foreign guns are calculated values. The penetration or the ballistics calculations could be incorrect.
    Look at the T-4 75mm tank gun. Only penetrates 74mm @ 1000m yet there is an article on this website. about a test of the effects of tracks having that reduces the penetration of the front hull of the T-34 from 1000m to 800m.

    1. Well, Mobius, we're at an impasse. Because my copy of A&B is identical to War Thunder's for not only the Soviet D-10 and D-25, but for everything else, including German and American weapons (are you saying that someone's tinkering with those too?). The only difference is that A&B has values every 250 m while War Thunder usually omits these.

      As to the KwK43 on that table. The foreign guns are calculated values. The penetration or the ballistics calculations could be incorrect.

      Are these calculated values? (I should ask 'solely calculated', because even physical testing results require calculations). Peter did not mention anything on the post about that, but instead rather strongly inferred that they were from actual tests (which the Soviets most certainly did of German weapons, Peter provides photographic evidence). The difference between "232 mm penetration", "203 mm of penetration", and "168 mm of penetration" derive solely from using different testing protocols.

      Only the second table Peter presented in a followup post contains presumably calculated data (because this was of foreign guns the Soviets did not have at-hand).

    2. Mr. Sampsonov was deliberately misleading in this article. All penetration numbers therein are calculated with a De Marre K=2400 as the front page of the document in question explicitely states:


      The values therefore are a red herring as far as german guns are concerned and would only be valid for a specific projectile quality, which matches exactly soviet domestic experiences. M. Krogfuss article about soviet ww2 projectile acceptance data and the use of De Marre K therein.

      Take the 50mm PAK38 (V0=835m/s). At 1000m the tabulation record a penetration of 47mm at 90° with K=2400.
      NII48 tests with captured life 50mm Pzgr39 instead (actual firing trials, not calculated tabulations) record the PSP definition of 45mm high hardness 8-S grade steel for 90° with 360m/s, which is >2000m. Quite a difference.

    3. Thanks for posting your conspiracy theory again. I'm going to show you the same thing I showed you the last time. This is Soviet 80% penetration data and British 50% penetration data. The British tests, naturally, show higher penetration due to the lower required success chance, otherwise the curve is the same.

      So are the British in on this conspiracy too, in your opinion?

  5. My apologies you have read the Scribed copy correctly. It however isn’t what my copies say it is. If that is a altered copy it is a good one. I have first edition and two 2nd editions. If there is a 2B edition it is news to me.
    I scanned the page as it appears in the books I have.

    I could email Robert Livingston and ask if there were changes made mid 2nd edition.

  6. These documents have caused quite a few debates in internet forums over the last years, especially the statement on the Panther's penetration from +2,000 meters. IMO the decision to stick with 122 mm was correct because:

    - Production was large enough to supply tanks.
    - Slower ROF was not that different when operating in a turret.
    - Better HE performance, which was main objective.
    - Penetration performance was similar in both guns, 122 being better in some cases