Sunday, 19 June 2016

IS-3: The Tank with a Piked Nose

The order to produce a new tank under the index IS-3 was received by Chelyabinsk factory management on December 16th, 1944. By January 25th, 1945, eight of the ten planned tanks had to be built. It took a fairly long time to build and "tune" the tanks, and they arrived in the army only by the time that the Second World War was at an end.

Goals Set by War

Spun once, the flywheel of Soviet design bureaus built up an unseen inertia by the time the war was coming to an end. Designers in Siberia, the Urals, and on the Volga overtook their colleagues in allied and enemy countries. While the first IS-2 tanks were just driving out of the Kirov Factory in Chelyabinsk (ChKZ), the design bureaus of ChKZ and factory #100 already received order #5583 from the State Committee of Defense on April 8th, 1944: design a new heavy tank. An analysis of tanks from early 1944 showed that Tigers could penetrate the cast front plate of early IS-2s from 1000-1200 meters and the Panthers could do it from 900-1000 meters. It was necessary to increase the protection of the IS-2 so that the front of the hull and turret as well as the side of the turret and the turret platform were impenetrable to German shells.

The ChKZ design bureau, headed by N.K. Dukhov and M.F. Balzhi, began its work. Their competitors from factory #100, headed by G.N. Moskvin and V.I. Tarotko also did not sit still.

Competition of Chelyabinsk Tankograds

The situation that developed in Chelyabinsk in the later half of the 1940s deserves a special mention. The decision to spin up tank production at the Chelyabinsk Tank Factory (ChTZ) was made even before the war. On June 19th, 1940, the Central Committee of the Party and Government of the USSR instructed ChTZ to begin production of KV tanks designed by the Leningrad Kirov Factory (LKZ). A special tank department was created at the factory, which included both local engineers and specialists from Leningrad. In August, ChTZ received a KV tank and blueprints. In the second half of 1940, the factory produced all parts locally, and the first ChTZ KV was assembled on December 31st, 1940. A building for a tank assembly plant began construction.

In the summer of 1941, war broke out, and trains of evacuated factories flooded Chelyabinsk. On September 12th, the GKO decided to move Kharkov diesel engine factory #75 to the city, and on October 6th, train cars with LKZ equipment and staff followed them. On the same day, the "Stalin ChTZ" was renamed "NKTM Kirov Factory in Chelyabinsk". The director of the new organization was the former director of LKZ, I.M. Zaltsmann, and the chief engineer was the former chief engineer of LKZ, Zh.Ya. Kotin.

Aside from the aforementioned organizations, Chelyabinsk became the new home for equipment and specialists from the Molotov tool factory, Moscow Red Proletariat tool factory, and the Dynamo tool factory. Later, in 1942, a portion of the equipment from the Dzerzhinskiy Stalingrad Tractor Factory (STZ) was evacuated here. All equipment could not be recovered, as German tanks reached the factory while the evacuation was still underway.

These resources, brought here from the entire USSR, formed an enormous production base, nicknamed "Tankograd". Along with workers and tools, it had the minds that created the best tank engine of the war, the V-2, which went into all heavy and medium tanks and SPGs produced during the war in the USSR. In addition, Chelyabinsk inherited almost the entire engineering team that designed the KV-1 tank.

The new chief engineer of ChKZ, Zh.Ya. Kotin, liked working independently. Using all of his connections in the NKTP, he initiated the creation of an experimental factory within ChTZ, which he headed himself, and where most engineers from ChKZ were transferred, even though physically they continued working at ChKZ. This created two competing design groups which would not allow each other to rest on their laurels.

Difficult Road to Perfection

In the spring of 1944, both groups were given the same task. Factory #100 decided to not deviate too far from their previous design, the IS-2. Instead of one piece, the upper front plate was formed from two 110 mm thick pieces welded together in the middle, sloped in the vertical plane and turned at a large angle. Their top was covered by a roof that was sloped 7 degrees from the horizontal. This design was initially called "hooked nose", but later earned the title "pike nose". The angles to the horizontal and vertical planes forced enemy shells to ricochet.

Factory #100 designers rejected large cast components due to progress in electrical welding at the Paton institute, evacuated from Kiev, as well as the overloaded ChKZ casting plant, which produced IS-2 turrets. In addition, rolled armour has superior properties compared to cast armour.

The Kirov factory design differed in its original flattened hemispherical turret, designed by G.V. Kruchenykh. It housed the same 122 mm D-25T gun from the IS-2. The perimeter armour reached 110 mm in the top and 200 mm in the bottom. The steep angle (60 degrees) of its walls improved the chance of ricochet. The floor of the new tank was V-shaped, which allowed the reduction of vertical hull armour and further reduced the mass of the tank.

Experimental prototype of the Kirovets-1 (Exhibit A) developed at ChKZ.

Both prototypes rejected the hull machinegun and hull radio operator. The freed up space and mass were used to improve the armour of the tank and increase the space available to the driver.

Two independent projects were sent to the People's Commissar of Tank Production, V.A. Malyshev. One from ChKZ director Zaltsmann and chief engineer Dukhov, the other from the director and chief engineer of factory #100, Kotin.

The factory #100 prototype made it to factory trials first, on October 28th, 1944. Its journey along the Brodokalmakskiy track revealed several major defects in the design of the drivetrain, and the tank was returned to the factory for corrections. The second 1000 km march in November showed that the engine and transmission problems never went away. 

The second prototype received the index Kirovets-1, even though Zaltsmann had the more grandiose name "Pobeda" (victory) in mind. The military representatives were much more practically minded and named the tank simply: Exhibit A. Its trials lasted from December 18th to December 24th, 1944, and mostly satisfied the military, although the factory was recommended to fine tune their tank.

The fine tuning turned into a whole new tank. In parallel with these trials, the designs were analyzed at the Institute of Armour and Metallurgy (TsNII-48), which worked in Sverdlovsk after its evacuation. TsNII-48 specialists combined the best solutions from each of the projects into one tank. The factory #100 project contributed its piked nose and the ChKZ project contributed its pancake turret, which was stretched out into an ellipse. The V-shaped hull also migrated to this tank. The theoretical probability that this new hull would be penetrated by an 88 mm shell decreased to 34% from 39.5% of the factory #100 hull and 44.1% of the ChKZ hull. 

Order #729 on the creation of a new tank was received by directors of both factories on December 16th, 1944. ChKZ was to immediately produce a 10 vehicle pilot batch. The new tank was not named Victory, although Zaltsmann could claim a consolation prize: the index "703" that was given to the new project indicated a ChKZ victory, since factory #100 designs had 200-series indices. ChKZ had to build ten 703s by January 25th, 1945.

Soon, the new tank received its "fighting" index: IS-3. Even though the tanks were similar to the IS-2, production and tuning of the new tanks took a long time, and the tanks only reached the armed forces by the time that the fighting was done.

Technical Characteristics

The IS-3 had a classical layout. The suspension was not modified compared to the IS-2: there were six doubled road wheels per side with individual torsion bars and three return rollers. The track was driven by a pin-wheel gear. The rear engine and transmission drove the rear drive wheels, which were equipped with removable crowns with 14 teeth each. The idlers, completely identical to the road wheels, were in the front. The tracks were 650 mm wide, and each track consisted of 79-86 links that were 160 mm long.

The hull had a pike in the front and a V-shaped floor. The pentagonal driver's hatch was installed above the pike nose and opened sideways. The hatch contained a periscope which could be removed when the driver left the tank. Another emergency hatch was placed behind the driver.

The upper part of the hull, 90 mm thick, was given a reverse slope, which both made it harder to penetrate and allowed for a bigger turret ring. The rear part of the hull could flip open to simplify access to transmission and engine components.

The biggest difference compared to previous models was the hemispherical turret. Oddly enough, it lacked a commander's cupola, even though all other tanks produced in the USSR at the time had one. Observation devices were installed in openings cut into the hatches. The right half had the loader's MK-4 observation device, the left half had a TPK-1 for the commander. Another MK-4 for the gunner was installed in the turret roof. The turret turned with an electric mechanism with the maximum speed of 12 deg/sec.

Three members of the crew were positioned in the fighting compartment: the commander, gunner, and loader. The main armament of the tank was the same as on the IS-2: a 122 mm D-25T gun mod. 1943. The semiautomatic sliding breech allowed a rate of fire of 2-3 RPM. The ammunition rack consisted of 28 shots, 10 AP and 18 HE-Fragmentation. The TSh-17 gun sight allowed for a maximum direct fire range of 5,000 m and 15,000 m indirect fire range with the Hertz panoramic sight. A special mount on the roof housed a 12.7 mm DShK AA machinegun with 300 rounds of ammunition: 6 belts of 50 rounds each. The 7.62 mm coaxial machinegun had 945 rounds of ammunition: 15 magazines of 63 rounds each.

The engine compartment housed a 12-cylinder 4-stroke 520 hp V-11-IS-3 engine. The tank's transmission consisted of a multi-disk dry friction clutch and an 8-speed gearbox with a demultiplexor and two-stage planetary turning mechanisms. The tank had floating band (iron on steel) brakes and the final drives had reduction gears with a simple six-gear and planetary stages.

The tank had four internal fuel tanks with a total volume of 450 L, two per side. In addition, the tank could have four external cylindrical fuel tanks, 90 L each, which were placed on the rear part of the hull and connected to the internal tanks. In case of ignition, the tanks were equipped with a mechanical jettison system. The handles for dropping the tanks were positioned in the rear of the fighting compartment.

IS-3 tanks used 10-RK-26 radio stations and TPU-4bis-F intercoms.

On February 20th, 1945, the reference IS-3 tank #2 was sent to government trials at the Kubinka proving grounds. Trials lasted from March 23rd to April 12th, 1945, and concluded successfully. By May 1st, 1945, ChKZ produced 25 IS-3 tanks, some of which were still undergoing factory testing.

The tanks reached the military fairly late, and due to a lack of trained crews, did not fight against either Germany or Japan in WWII.

The first official showing of the IS-3 occurred on September 7th, 1945, during the Allied parade in Berlin to mark the end of WWII. 52 tanks from the 71st Guards Heavy Tank Regiment of the 2nd Guards Tank Army drove along the Charlottenburg avenue. Foreign military observers were shocked at the presence of such powerful vehicles in Soviet hands. In the future, hysteria in Western press about Soviet tanks on the shores of La Manche was caused by this show of force. In the USSR, the tanks were first shown on the May 1st Parade in 1946.

These new tanks had a series of disadvantages that had to be corrected. The biggest weaknesses were the engine and transmission, which weren't quite enough for a 46.5 ton tank. The small ammunition capacity and two-stage loading process also drew criticism. The tank's low speed was also unsatisfactory, and production ended in the summer of 1946. Only 2310 IS-3s were built, at a cost of 267,000 rubles each.

The IS-3 tanks went through several modernizations. In 1948, designers reinforced the engine mounts, changed the mounts for the gearbox and the main friction clutch design, replaced the 10-RK radio with a 10-RP radio, and the hand fuel pump with an electric one. The cost of modernizing one IS-3 was between 190,000 and 260,000 rubles, but the result was still unsatisfactory.

In the early 1950s, more work was done on the IS-3s: the robustness of the hull was improved with ribs in the rear and on the bottom. The biggest changes lay in the engine, which was replaced with the modernized 520 hp V-54K-IS with a VTI-2 air filter which had a two-stage filtering process and a dust ejector. To place the gearbox deeper in the hull, a slot was cut out and the opening was welded shut, leaving a bay for the gearbox. The DShK and DT machineguns were also replaced with modernized versions.

The four 90 L tanks were replaced with two 200 L ones, and the driver was given a new TVN-2 night vision device. The padding of the commander's rotating hatch was changed. A two-series light was added to the electrical system, and an external jump-start outlet was added to the rear. The controls and instruments were replaced with electric ones, and R-113 radios and R-120 intercoms were installed. The tanks received a new index: IS-3M.

In the Red Army (from 1946: the Soviet Army) IS-3 tanks were mainly used to outfit the German Occupational Force and forces in Eastern European countries.


  1. "The decision to spin up tank production at the Chelyabinsk Tank Factory (ChTZ) was made even before the war. On June 19th, 1940(...)"

    The Second World War started on September 1st, 1939. USSR took active role in it since September 17th, 1939. So no, it was not "before the war". Do not mix The Second World War ("the war") and The Great Patriotic War in one article, please.

    1. Very offended people for everything, but actually don't care about the article, the IS-3 or whatever. He obviously refers before German invasion on Soviet Union... but very offensive, never do it again ¬¬

    2. When a Russian says "the war", he is referring to the Great Patriotic War. I'm sure every culture has its own default war they refer to.

    3. It can be equally argued that WW2 started already with the onset of the Second-Sino-Japanese War in July '37 - recall that said quagmire kept going nonstop until the Japanese surrender, and tied up ludicrous amounts of resources for preciously little gain. By comparision the USSR was at peace from early '40 to late June '41 - in practical terms their earlier Central European opportunism (and something of a bloody nose in Finland) were as separate conflicts as their earlier skirmishes with the Japanese in Manchuria.

  2. Thanks a lot for the interesting article.

    May I ask why the weight in this article is referred to as 56.4 tons while in the older IS2 vs IS3 article the weight was tabulated as 46.0t. to 46.5t

    10tons of difference are making me curious.

    1. That's a typo, it should be 46-46.5 tons.

  3. I dont understand why IS-2 didnt get turret with reinforced frontal armour along with modified hull. While it could resist Kwk 36 and Pak 42 AP shells it was helpless against its subcalibers. Turret front coul be modernized with new mantled similar with its design to IS-3, IS-4 or IS-6 mantled.

    1. German subcalibers weren't exactly a major problem AFAIK. Those are made of tungsten which they were pretty seriously starved for and also needed for a bunch of other things (eg. machine tools).

      IIRC even the Americans, who had unhindered access to the global markets and damned near a surplus of both funds and industrial capacity, could only issue APCR in rather miserly quantities. The Brits weren't much better off with their APDS, but both could more or less reliably supply *some* to the front. Conversely AFAIK the Germans, for the most part, just had to get by without.

    2. There was a wide variety of german subcalibre ammunition and not all was used in AT-role.

      [1] full calibre Tungston-carbide cored AP-shot
      Lighter than full calibre APCBC, reulting in higher velocity, usually the penetrator was shielded by light material

      [2] sub-calibre arrow type tungston carbide shot
      Initially for tapered bore guns, later generally adopted for guns without muzzle break, similar to [1] but better downrange performance

      [3] Sub calibre discarding ring HE
      Used for artillery and FLAK to obtain longer ranges / higher ceiling, frequently used

      [4] Sub calibre discarding ring APCBC
      Full calibre AP projectile with discarding sabot. F.e. 15cm/10.5cm - 12.8cm/8.8cm -10.5cm/7.5cm
      Usually used for artillery as AT projectiles. Increased velocity, performance similar to APCBC of ATG but larger dispersion. Doesn´t require special ressources like tungsten-carbide. Commonly used late in ww2 at long range anti-tank by artillery due to HEAT more suitable in close range AT role.

      [5] Sub calibre discarding ring, fin stabilized HE
      "Röchling" derivates for very long range artillery.

    3. I concur with your assessment, Crabtree. The IS-4 was sort of an attempt to do what you suggest, but it (like the T-44 in comparison with the T-34/85) made a lot of other changes that complicated the design. In addition, the IS-4 went absolutely nuts on armor protection (I mean, *160 mm* on the hull sides and 200 mm on the turret sides?) which contributed mightily to its 60-ton weight, and it was said increase in weight that mandated a new engine and cooling system plus other changes. The tactical mobility of the IS-4 wasn't bad, but the operational mobility (the ability to cross bridges and obstacles) suffered as a result of that weight, plus its reliability. One of the merits of the IS-2 which kept it in service past the IS-3 and IS-4 was its good mechanical reliability and ease of maintenance.

      There was the IS-2u, which not only tried to upgrade the front turret armor but also slope the lower plate to an effective thickness, but even doing that required some redesign changes, so it's not as trivial as one first would think:

      But, still, if one could have upgraded the IS-2's turret to have something more like the frontal protection of the IS-3, slope the lower front plate more like at 55 degrees to eliminate that weak spot, and (maybe, if possible without overly increasing weight) modestly increase the side armor (to 100-120 mm) to make it more resistant to side shots from guns like the Pak40 75 mm and US 76 mm, all without increasing the weight much (say, to 50 tons) then you might have it. A slight loss in tactical speed for a breakthrough tank like the IS (after all, these are supporting infantry attacks) isn't as much of an issue as operational mobility, the ability to cross bridges and obstacles; losing a couple km/hr road speed could be acceptable if you can still cross bridges.

      Lastly--an observation on Russian heavy tank organization--an independent heavy tank brigade is cited to have 19 armored transporters, 3 BA-64 armored cars, and 3 SU-76s. Why were the SU-76s attached? And why was not a contingent of combat engineers? I'd think you'd want the engineers attached to reinforce bridges and things.

  4. I have lost the reference, but I understood a company of IS3 fought in the Manchurian offesive of 1945. Have you got any information about it?

  5. Do You happen to know how the pike nose was assembled? Was it cast or welded? And if the latter applies, how much work was done to interlock the individual plates. I have been at a loss to find much interlocking at all but am not too familar with this question.

    1. Welded, somewhat obvious in the WoT hangar if you happen to have one. (The trickiness of the shape and thickness of the plates resulted in considerable variations in exact angles between individual tanks IRL, AFAIK.) The Soviets seem to have long preferred that construction method for hulls from what I gather.

      And if by "interlocking" you mean the kind of jigsaw puzzle the Germans played in their heavier tanks, I'm under the impression that was highly uncommon because it was a lot of extra work and not usually needed - Ze Germanz did it out of necessity, due to shortages of alloying elements for the steel and not unrelatedly using plate thicknesses at the limits of what applicable period welding technology could manage.

      Related: AFAIK burst weld seams were a common complaint from the units kitted out with the heavier tanks (starting with the very first batches of Tigers into combat), and also routinely noted in Allied and Soviet ballistic tests done on captured examples.

  6. The germans made, I think, a reasonable decision. Interlocking plates added a significant amount of structural strength to the hull, the plates supported each other at the interlocked edges. It just wasn´t enough to break the welds to make a plate fall off. And considering the tendency of hydrogen embrittelment present in welds, that made a lot of sense.

    The method was pioneered by Krupp for KC plates in battleship armour in the period 1905 to 1910, in order to add structural strength and distribute stress more equally over larger areas. It appears that most nations followed that line of construction later as it removed areas of weakness (f.e. LION´s driven in belt plate at Doggerbank from a long range, high obliquity impact -resulting in the near loss of the ship- would be adressed effectively by interlocking plates).

    In tank armour, it was less common, until the early 40´s but I was under the impression that the complex structural geometry of the pike nose in particular would benefit a lot from an interlocking design. Weld seams can´t be relied upon not to give way under repeated or severe shock (particularely at low temperature as V-notched Charpy impact tests revealed), interlocking plates can. It didn´t add weight, but a significant amount of complexity, true.

    1. The weld seams of Tigers in Tunisia apparently started to give trouble in under a week of combat against nothing more formidable than, what, 6-pounders and the Grant/Lee's medium-velocity 75 mm tops. I don't know if the secondhand Egyptian IS-3s ever had seam trouble, but the IDF apparently did regard them as effectively invulnerable from the front - and they were shooting 105 mm's at them.

  7. Tigers weld seams starting doesn´t surprise me. It actually would surprise me if they don´t start to crack open after repeated or severe impact. However, interlocking plates offer structural rigidity in case the welds are broken. A condition which, considering all we know from battle damage reports, has to be realistically reckoned with.

    1. The point is weld seam failure primarily turns up in the context of the German heavies, and was noted by both themselves and their enemies. If the latter had comparable problems - the thick-skinned KVs and ISs would particularly appear potential candidates - then I've yet to see that mentioned in writing despite any amount of *other* critique of their AFVs...

  8. Weld seam failure is catastrophic for structural strength if there are no means to reinforce plate attachment by, f.e. butt straps, laps, -or interlocking plate joints.
    The more complex interlocking, keying elements in german tank construction gave them considerable strength, not only in ballistic impact even if the weld seam failed but also by blast, f.e. through mine explosion.

    Thick plate, weld seam issues were reported for by egyptian IS3 post war under ballistic impact.

  9. It appears that by all critique of the 128mm L/55 PAK 44 /KWK, the weapon was suited for knocking out IS3 frontally at long range well before the IS3 was even introduced. The Hillersleben prooving ground minutes (report from Nov. 9th, 1944) give the penetration as follows

    128mm Pzgr.43:
    weight: 28.3kg
    initial velocity: 920m/s
    (5 out of 5) complete penetration RHA at 30°/0°:
    1000m: 202mm / 250mm
    2000m: 178mm / 219mm
    3000m: 155mm / 190mm
    4000m: 133mm / 164mm

    128mm Pzgr. 39 TS:
    weight: 9.85kg (APCBCDS-HE, using a subcalibre 88mm Pzgr 39)
    initial velocity: 1230m/s
    (5 out of 5) complete penetration RHA at 30°/0°:
    1000m: 264mm* / 325mm*
    2000m: 230mm* / 283mm*
    3000m: 178mm / 219mm
    4000m: 140mm / 172mm

    *) Only if projectile stays intact. Test projectiles from the 88mm subcalibre cores broke up about half of the time against RHA plate thicknesses larger than 200mm but regularely stayed intact at smaller thicknesses. 88mm subcalibre AP cores from the manufacturer Bochumer Verein always stayed intact.