Tuesday 16 October 2018

D-10 and IS-2

"To comrade L.P. Beria

On installing the 100 mm D-10 gun produced by NKV factory #9 into the IS tank instead of the D-25 122 mm gun made by the same factory

In March of this year, I reported to you that NKTP factory #100 jointly with NKV factory #9 produced an experimental prototype of the IS heavy tank with a D-10 gun designed by factory #9.

Trials of the IS with a 100 mm gun showed that the 100 mm D-10 gun has undeniable advantages over the 122 mm D-25 gun as armament of the IS tank. These advantages are as follows:
  1. The aimed rate of fire of the 100 mm D-10 gun in the IS tank is up to 8 RPM (on average 6 RPM), 2-3 times higher than with the 122 mm D-25 gun.
    This high rate of fire decisively improves the combat capabilities of the IS tank.
  2. A lack of a muzzle brake on the 100 mm gun improves the firing conditions for the crew in comparison to the 122 mm D-25 gun, which has a muzzle brake.
  3. The 100 mm D-10 gun weighs 300-400 kg less than the 122 mm D-25 gun.
  4. The dimensions of the parts of the gun that are housed inside the turret are less for the 100 mm D-10 gun than the 122 mm D-25 gun, making servicing the gun easier.
  5. The one piece round of the 100 mm gun is safer from the point of view of explosions and fires than the separate propellant of the 122 mm gun.
  6. The armour penetration of the 100 mm D-10 gun is greater, however slightly, than that of the 122 mm D-25 gun at ranges of up to 1000 meters.
    The 100 mm D-10 gun can penetrate the armour of all known tanks at a range of 2 kilometers, except for the front armour of the Panther tank and Ferdinand SPG.
Considering that factory #9 managed to create a 100 mm gun based on a family of guns already in service (85 mm D-5, 122 mm D-25) and that does not require serious changes to the design of the IS tank, I consider that it will not be difficult or time consuming to begin production of the 100 mm D-10 gun at factory #9 (instead of the 122 mm D-25 gun) and installation of this gun in the IS tank at the Kirov factory.

Considering the above, I consider it imperative to begin producing IS tanks with the 100 mm D-10 gun in place of the 122 mm D-25 gun.

If you are in agreement, I ask you to task the People's Commissariat of Tank Production and the People's Commissariat of Armament to prepare a draft GKO decree on this issue.

V. Malyshev
April 25th, 1944"


  1. Which version of experimental IS was this? The "IS-4" or "IS-5"?

    Also of interest, I recall a similar archived period document from the battlefield.ru site years ago which claimed the D-10 offered no convincing advantages over the D-25, in either terms of storage, rate of fire, or penetration.

    1. It was not given a seperate number. IS-4 was a serial produced tank for one that essentially had a beefed up IS-2 mod.44 type hull with a somewhat flattened turret and the same 122mm D-25T gun, later upgraded to a 122mm M-62-T2 gun. IS-5 through 9 were various prototypes, most well known being the IS-7 for actually being really good.
      Other than that, the main reason they didnt end up using the 100mm gun was that the gun was relatively new so both guns and ammo were in shorter supply than the 122mm which used the same ammo as the A-19 gun, which had been in service and production quite long by then.

    2. The IS-4 was armed with a D-10T gun, the IS-5 was armed with a 100 mm S-34 gun. @The Builder: you are correct that the IS-4 (Object 701) was a different tank, but this IS-4 had the factory index 245. Reusing letter indexes was a common feature of Kirov factory. There were also multiple IS-1s, IS-2s, KV-3s.

      Also as far as I am aware no IS-4 (701) was ever retrofitted with the M-62 gun. This modernization was possible, as the gun fit into D-25 trunnions, but the IS-4 was no longer in use by the time it was developed.

  2. @The Builder, the reason I put the "IS-4" and "IS-5" in quotes is that they were wartime experimental IS-2 Mod 1943 versions, unrelated to the postwar IS-4, with different internal seating arrangements (reversing gunner and loader, and switching the commander's cupola to the right side of the turret). The "IS-5" at least they also turned the gun mantlet upside-down to flip that too.

    There are pictures of the IS-4 in Baryatinskiy's book. Here is a War Thunder thread with pictures of both:


  3. Also the web page contains the counter-arguments against any variant of the 100 mm being the main gun of the IS tank:

    However, in Malyshev's letter to Beria on October 18, 1944, he wrote: "...[122 mm guns] can now fight any German tank at a distance of 1700 meters and greater..."

    The following points supporting the IS-100 were outlined in the letters between Malyshev, Beria, and Fedorenko:

    Increased rate of fire (up to 8 rounds per minute)
    Increased ammunition capacity
    Lack of muzzle brake improves working conditions for the gunner
    The tank is 500-600 kg lighter, which allows for additional armour
    Smaller size, leading to a roomier turret
    Higher penetration
    Factory #9 was ready to produce D-10T guns along with D-10S

    Points against the IS-100 in the same series of letters:

    D-25T is already sufficient against German tanks at all combat ranges
    Reduced caliber will reduce HE effectiveness against enemy fortifications and soldiers
    The increased ammunition capacity is negligible (29 rounds instead of 28)
    A large caliber, high rate of fire semi-automatic gun will lead to high concentrations of gases inside the tank

    Additionally, in a report from the Chief of Experimental Machinery to the Chairman of the Technical Council, the superiority of the D-10T to the D-25T in armour piercing capacity is challenged:

    "[The D-25T] penetrates a Panther frontally at 2500 meters, and that is not the limit. The 100 mm D-10T tank gun ... penetrates the front of the Panther at only 1500 meters, which is the maximum distance. ... The results are preliminary, as the D-10T has already fired 400 shells while the D-25T is new, but the difference is so drastic, that it is unlikely to change. "

    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.

  4. By 1945 I bet the Russians just like the American's found their primary concern was engaging German fortified positions. The American's made do with up gunned Sherman's with 105mm's and Jumbo Sherman's with extra armor. As IS 2 with a 122mm is the best of both worlds.

    1. I'm not sure the 105mm howitzer variant could be called "upgunned"... certainly better at Blowing Stuff Up but better hope you didn't need too much penetration, given the relative primitiveness of the HEAT shell.

      Random aside: always puzzled me that there wasn't a howitzer variant of the "Jumbo", seems like it'd have been an excellent fit for its "assault tank" role.

    2. Agreed, since the M4A3E2 was explicitly designed as an assault tank, I too am surprised they didn't get a 105mm howitzer.

    3. Kellomies. I very much agree the Jumbo Sherman would of been a obvious choice for the 105mm Howitzer. After the Battle of the Bulge most of our engagements were against dug in infantry and guns.

  5. Engaging fortified positions has been a concern from the Winter War. The army wanted a high velocity 152 mm gun in an SPG chassis. The only options given to them were either a high velocity 122 mm gun or a 152 mm gun-howitzer, neither of which were entirely satisfactory.

  6. Hi!

    Thats my second comment on Tank Archives (I write one comment under "unknown" nickname). On Polish internet forums some poeple know me under AKMS ans SMKA nickname.

    On This blog one commentator (William Sager?) was wondered why Soviets use in WW2 magazine feed tank machine guns. In my opinion, thats not strange. Firstly, not only Soviets use magazine feed machine guns in tanks. Also French, Italian nad Japanase tanks use magazine feed machine guns. Secondly, on Polish internet forum about WWII I found information that during interwar period Polish tankers prefer magazine feed over belt feed in machine guns (belt reload was problematic in tank interior). From other hand, Polish 7TP tank use belt feed ckm wz. 30 machine gun.

    And In my opinion, DT machine gun it's pretty good weapon. Maybe it's better gun in tank machine gun role that DP in infrantry machine gun role. I think that, because one of DP/DT flaws, don't be important in a tank. I think about a bad ratio between magazine capacity and weight. As example (data from Polish "Współczesne karabiny maszynowe/ Modern machine guns" book)- one ammo box with 200 round belt for modern PK machine gun have a 8 kg weight. For comparision, 4 DP magazines, which hold 188 rounds (one magazine hold 47 rounds) have a 11,2 kg weight. This is importaint in infrantry, but not in 30 or 45 tons vehicle (in tank, machine gun ammo weight it's a very small part of vehicle combat weight).

    1. The problem with magazine-fed MGs is its much harder to sustain fire. With a belt-fed gun you can typically go at least 100 rounds (if not a lot more depending on how the belt is constructed) before reloading. I've never handled a DT or DP so I don't know how long a magazine change took, but changing out a belt is usually pretty quick. I hear what you're saying abut space restrictions though.

    2. I agree that typical MG belt hold far more rounds than typical magazine. But from other hand, DT magazine hold 63 rounds. Thats not small number of rounds. Of course, I agree that belt feeding it's better idea for tank machine gun, but in my opinion, some magazine feed machine guns, can be used as pretty good tank machine gun. BTW, in my opinion, in belt feed tank machine gun, exist a difference between a situation, when tank machine gun use pretty short belt, and situation when tank machine gun use a extremly large belt located in extremly big ammo countainer. As example, modern BMP-1 have a ammo container for 2000 rounds belt. I don't know any WWII tank which use similar ammo container. As example, IIRC German WWII tanks use 150 rounds belts in tank machine guns.

    3. As a infantry weapon the DP is pretty good. It's the poor guys forced to drag around Maxim machine guns I felt sorry for. Indeed what seems strange is that the Soviets developed lots of air craft machine guns, but waited until 1943 to introduce the SG-43. The cost of producing M-1910 Maxim machine guns must of been huge and used a lot of resources. The British Vickers was big and heavy at 40 lbs, but the Maxim was almost 60. Indeed it was so heavy they required a heavy mount to carry around.

    4. The Army backed itself into a corner by demanding that a) the 7.62x54r cartridge was used and b) the round was pushed straight through when chambered instead of pulled out backwards like in the Maxim. This made designing a belt fed machinegun pretty much impossible.

    5. Yeah, push-through seems a wee bit physically impossible with a fully rimmed cartridge (or at least would impose considerable amounts of pointless mechanical complexity for workarounds). Rather makes me wonder about how such a self-evidently impossible set of requirements came about in the first place; were the people composing it actually that thoughtless if not outright incompetent, or did someone with sufficient pull have some manner of unhealthy fetish for magazine feed and/or irrational hatred for belts?

    6. Peter Samsonov I fully share your anti rimmed cartridge bias. But they could of designed a smaller Maxim style weapon. Look at the Vickers Machine Gun. Though to the Soviet's credit they eventually built the PK Machine Gun which used the same 7.62 rimmed cartridge.

    7. William Sager, exist a Soviet infantry belt feed machine gun, introduced after Maxim, and before SG-43. DS-39. But most source show that this is not great gun.

      Kellomies- IIRC, exist a gun which use a belt feed, rimmed cartridges, and push-through system. Kulomet vz. 59. But this is postwar gun.

    8. I've no doubt that with sufficient ingenuity it is *possible* to devise a feed system capable of the trick, but it seems rather impossible to achieve without considerably adding to the complexity of the mechanism for dubious gain which somewhat calls into question the point of the entire exercise.
      Certainly the "mainstream" MG families chambering the venerable 7.62x54mmR just bite the bullet and stick to the proven old "pull-out push-through" solution, ie. the cartridge is first pulled rearwards out of the belt and then fed into the chamber. (Quick look at modernfirearms.net says both the DS-39 and SG-43 used this too, by the way; probably unavoidable as both used non-disintegrating belts.)

    9. I agree that push-through system can be problematic in MG which use rimmed ammo- I know only one MG which use push-through system with rimmed ammunition (Kulomet vz. 59). But from other hand, I don't have any information which suggest that Kulomet vz. 59 have extraordinary complexibility of feed system.

      In my opinion push-through system is impossible to use if MG use a belt with "closed links". I put 2 drawings- on left, "open link", on right, "closed link" (I don't know what is correctness of this terminology in English). In my opinion that can be reason for use "pull-out push-through" system in PK- IIRC PK can use SG-43 belt, and this belt have "closed links".



      BTW, If exist a MG non-desintegrating belt which use "open links", propably this belt can be used in MG with "push-through system".

    10. Yea, the Czechs got around it with creative belt design:

      Near as I can see the sole benefit of this trick is saving some mechanical complexity in the feed system as the cited standalone gun weight is only marginally less than the original PK's, it and may have come with belt robustness issues or somesuch given the idea hasn't exactly caught on widely.

    11. Kellomies, I think that you are right. Also in my opinion "push-through" system don't must mean smaller weight. Oryginal PK/PKM use old "pull-out push-through", and PKM don't have bigger weight than Polish UKM-2000 (this gun use "push-through" system). In my opinion this is VERY interesting comparision, because UKM-2000 based on PK/PKM machine guns.