Saturday 29 December 2018

The KV's Last Bow

It is often the case in many nations that instead of new tanks, industry preferred improved versions of tanks that were already in production. The Soviet tank industry was no exception in this regard. That was the start of the history of the T-60, for example. Factory #37 proposed that an improved T-60 with a 45 mm cannon and improved armour be built instead of the T-70. That time the gamble didn't succeed, and the T-45 remained experimental. In 1942-44, a the story repeated itself with the heavy KV tank, which brought to life the KV-100 and KV-122 tanks, the tale of which this article will tell.

Simple to master

The main reason for putting improved tanks in front of brand new ones was ease of production. Recall the history of the KV-1S tank. In the spring of 1942, when the Red Army needed a tank that was as agile and small as the T-34 but with better protection, Chelyabinsk began designing the KV-13. However, the speed at which a tank could enter production was a decisive factor in wartime, and because of this the "small modernization", the KV-1S, went into production instead. While the KV-1S was being produced, two new variants of the KV-13 were created. The KV-1S remained on the conveyor belt while the Object 237 was born and later turned into the IS-85 (IS-1).

The KV-85 went into production in August of 1943. The tank was supposed to remain in production while the Chelyabinsk Kirov Factory (ChKZ) mastered the production of the IS-85. The desire to ease the life of the factory again led to mixed results. Last time production of the KV-1S turned into a real life drama. The story repeated itself, and the KV-85 managed to get on the factory workers' nerves. The simplicity of its production turned out to be questionable. It turned out that moving over to brand new IS-85 and then IS-122 tanks was not that much more difficult.

A comparison of the mass of the KV-1S, KV-85, IS-85, and KV-85 modernization project. A difference of 60 kg seems a little optimistic.

A switch to the IS-85 could have been avoided entirely. In August of 1943 ChKZ was working on an alternative heavy tank envisioned by the factory's director, I.M. Zaltsmann. Issac Moiseivich received this post after being removed as the People's Commissar of Tank Production. The project can also thank the factory's chief engineer, S.N. Makhonin, for its existence. The idea is told in a report composed on August 22nd, 1943.
"In parallel with preparation for IS tank production, which is a new design, the Kirov factory tasked itself with finding a solution and providing a tank that meets the same tactical-technical requirements as the IS tank, but has the following advantages:
  1. Uses the components and assemblies of the production KV tank, which allows it to be built without decreasing the output of tanks. 
  2. Production of the SU-152 SPG at the Kirov factory and factory #200 can be preserved. 
  3. Production of KV-1S and SU-152 spare parts can continue, which are still used by the army and can be used without retraining personnel who are used to fighting in KV tanks."
No drawings of this project remain. However, based on the report one can assume that the KV-85 was taken as the starting point by Dukhov's SKB-2. The turret would be the same as the one used on the KV-85 and IS-85. The protection was improved compared to the original tank. The thickness of the sides increased to 90 mm and the rear up to 75 mm.

The front of the hull is the most interesting part. According to the description, the thickness of the armour increased to 90 mm, and the shape of the plates changed. The top plate was angled at 30 degrees, and the bottom at 60 degrees to horizontal. The front of the improved KV-85 was theoretically more protected than the front of the IS-85.

A KV-85 with a 100 mm S-34 gun, Gorohovets ANIOP, January 1944.

Due to the small amount of changes necessary to the initial tank, first improved KV-85s could be expected by September 15th, 1943. However, no orders for the modernized KV-85 came from either the NKTP or the GBTU. Development was done entirely on the factory's initiative.

There were some questions about the modernized tank. It was supposed to weigh 45,342 kg, while the production KV-85 weighed 45,282 kg. It is doubtful that such a formidable upgrade in armour would increase its mass by only 60 kg.

In addition, the difficult work of building the first KV-85s was being carried out in late August. There were a number of issues with the production. Considering that the relationship between Malyshev and Zaltsmann was strained, the NKTP met his initiative without enthusiasm.

The peculiarities of the gun mantlet can be seen.

On August 26th, 1943, order #512 of the NKTP was composed. In it, the initiative of Zaltsmann and his men is harshly, but fairly, criticized. It was clear by that point that even the IS-85 was only a temporary solution. Experience at the Battle of Kursk showed that a heavy tank needs a more powerful weapon than a D-5T gun. Such a gun, indexed D-25, was being developed by factory #9's design bureau.

Calculations showed that the mass of the IS-85 with the D-25 gun grew to an acceptable 45-46 tons. The KV-85 and its potential modernization were a different story. The weight reached 47-48 tons, which was too much for the chassis. ChKZ's project was declined. It was time to work on building the KV-85 instead of fantasizing.

The last paragraph of the order was aimed specifically at the factory's leadership.
"The Director of the Kirov factory, comrade I.M. Zaltsmann, and the Chief Engineer of the factory, Comrade S.N. Makhonin, are warned that they are not to violate the existing order of developing new tanks and making proposals for altering the production of existing tanks."
Initiative work regarding the KV-85 ended here, at least for 1943. Production of the IS-1 began in November of 1943, and ChKZ delivered its first IS-2s in December. Putting these tanks into production turned out to be comparable to the difficulty of the KV-85. Malyshev and Kotin's point of view that the IS had to become the Red Army's main heavy tank won.

However, the KV-85 was still modernized further. This did not happen on the Kirov factory's initiative alone. The idea to improve the armament of the KV-85 was born at the Central Artillery Design Bureau (TsAKB), which was working on the S-34 family of guns. Like factory #9, the TsAKB was working on a triplex: three different barrels on one cradle. The number 34 was not used by accident, as the gun was based on the 100 mm B-34 naval gun.

The gun at maximum elevation.

The TsAKB was given one production KV-85 to install a B-34 in. Greater changes than with the D-25 were required to install this gun. The breech of the S-34 opened to the right, not the left, but the loader had to sit on the left. Because of this, the turret had to change significantly. The loader and commander swapped places, and the gunner's seat shifted as well. The sight and coaxial MG moved along with the gunner. The turret traverse mechanisms also had to be changed. The elevation flywheel was now to the left, and the traverse flywheel to the right.

The gun mount was seriously changed also. The gun mantlet changed, and the gun shield had to be made from scratch. It was much wider than the mantlet on the D-5T and D-25T. The ammunition racks on the experimental tank were not changed.

The rear machinegun bulge did not move along with the commander's station.

Installation of the S-34 into the KV-85 turret began in December of 1943 and trials at the Gorohovets ANIOP began on January 22nd, 1944. They continued until January 28th. 638 rounds were fired, 324 of which with supercharged propellant. Precision and accuracy of the system was deemed not entirely satisfactory. They were lower than on the BS-3 towed 100 mm gun. The difference was especially noticeable when firing armour piercing shells.

Firing on the move trials were also held. It turned out that this fire is ineffective, in part due to the effort required to operate the aiming mechanisms. The sight mount was deemed not well worked out, and a proposal was made to replace it with the superior TSh-16.

The rate of fire of the gun was its strong suit. With the gun at 2 degrees elevation, it reached 12 RPM. This rate of fire was achievable with a burst of 5 rounds taken from the turret bustle. With closed hatches and the fan turned on, two groups of 5 shells each could be fired off in 95-105 seconds. Therefore, the combat rate of fire was 5.7-6.3 RPM.

The rate of fire trials revealed the weakening of the aiming mechanisms and shell casing deflector. The function of the breech mechanism also slowly worsened. The muzzle velocity of the shell dropped by 14.4 m/s by the end of the trials, which was within norms.

The gun itself and the fighting compartment had to be improved as a result of the trials.

The S-34 passed trials, but the TsAKB was ordered to improve the gun. The placement of the crew inside the fighting compartment was deemed more or less acceptable, but the working conditions of the gunner had to be seriously improved, as well as those of the commander, who lost the extra space granted to him by the machinegun bulge. The commander's station was cramped and there was a risk of being hit by the gun breech when firing. One solution was to move the bulge to the right side of the turret. Also the TsAKB was ordered to develop an ammunition rack for the hull.

However, this was never done. The TsAKB was not planning on re-arming the KV-85, the experimental tank was just a test lab. The final goal was the creation of a 100 mm gun for the IS tank. Later, the TsAKB continued their work using an IS tank. This vehicle received the index Object 248. Work on the KV-85 with the S-34 gun (or KV-100 as it is sometimes called) stopped.

Local initiative

Even before work on installing the S-34 into the KV-85 turret began, OKB-172 in Molotov (modern day Perm) tried to arm the tank with an even larger gun. The artillery scientific prison began working on the OBM-53 122 mm gun in September of 1943, which would increase the firepower of the SU-152. The chief engineer of land artillery of OKB-172, M.Yu. Tsyryulnikov, directed this work.

All that is currently known about the OBM-51.

After the Battle of Kursk, an order was given to develop a 122 mm tank and SPG gun with 1000 m/s muzzle velocity. OKB-172 decided to combine the tank and SPG task. The OBM-51 project was complete by the end of October of 1943. Work was done within the scope of the task received from the NKV and the GBTU.

The project was reviewed during a technical meeting on October 26th. Only the description of the project remains, but even that makes it clear that only installing the gun was not enough. A new turret would be produced, larger in size. The gun would be installed in the tank using the SU-152's gun mount. The thickness of the front armour was 76 mm, the sides 60 mm, and the roof 30 mm. A 150 mm thick rear plate would compensate the length of the barrel. The KV tank with such a weapon would carry 45 rounds of ammunition in the turret and on the fighting compartment floor. The turret would keep the majority of it, more evidence that it would have to be much larger than that of the original tank.

KV-122, Chelyabinsk, spring of 1944.

The OBM-51 system was somewhat different than the SPG version of the gun. The length of the barrel was reduced to 58.5 calibers. The muzzle velocity was calculated to be 950 m/s. In addition to the main gun, the tank had its coaxial and rear machineguns.

The same tank with the turret forward.

A decision was made at the meeting to continue working on the project, with the development of the turret falling to OKB-172. Like the turret, the gun would also be changed. The plan to use the SU-152's gun mount had to be dropped, since it was too bulky. A more compact mount, like on the D-5T, was proposed. A horizontal sliding breech had to be designed, and the muzzle velocity brought back up to 1000 m/s. The turret ammunition racks were reduced to 30 rounds, and its size would decrease. The turret would also be made cast. The biggest change was that the IS tank chassis now became the priority. Both the chassis and the gun changed radically. The OBM-51 project turned into the better known BL-13.

Marks from ballistic trials that the Object 239 underwent in late 1943 can be seen.

The last attempt to boost the firepower of the KV-85 was undertaken in the spring of 1944. This work was also done on personal initiative, but the initiator remains unknown. Documents on this topic are few. The resulting vehicle is often called KV-122, but it is not known if this index was really used. Based on existing information, the lead engineer of this project was A.S. Schneidmann. The recipe for this project was simple: the experimental Object 239 chassis was equipped with a production IS-2 turret with a sliding breech D-25 gun. These turrets were not installed on IS-2 tanks before February of 1944.

There is some doubt about the mass of the rearmed KV-85, which allegedly was only half a ton greater than the Object 239. Based on the difference between the IS-1 and IS-2, the real mass of the KV-122 would have been around 47 tons.

The casting mark on the turret revealed that it survives to this day.

The initiative was doomed from the start. After the conversion, the tank's mass rose, which reduced its mobility and reliability. In addition, there was no sense in performing this conversion. By the spring of 1944 at least half of all KV-85s have already been lost in battle. A rearmament program for such a small number of tanks made no sense. The idea of the KV-122 never reached the Main Directorate of Tank Repairs of the Red Army, which would have been its chief customer.

Unlike the S-28 system that was planned for the KV-1S, there is not a word regarding this project in the report on ChKZ's experiments. No significant amount of information on the tank itself remains. According to the memoirs of N.F. Shashmurin, Kotin ordered for all information on the KV-122 to be collected and destroyed.

As a result, only a few photos and scraps of information survive to this day. The KV-122 managed to survive as well. Its lower half, the Object 239, is on display near Avtovo in St Petersburg. The top part, the turret with the armament, is installed on the grounds of the Kirov factory. It was installed on the chassis of an Object 237. No one knows if Kotin realized that every time he walked past the "IS-2" on the pedestal he laid his eyes on the very same vehicle that he wanted to erase all information on.


  1. The front of the hull is the most interesting part. According to the description, the thickness of the armour increased to 90 mm, and the shape of the plates changed. The top plate was angled at 30 degrees, and the bottom at 60 degrees to horizontal. The front of the improved KV-85 was theoretically more protected than the front of the IS-85.

    I'm either not visualizing this or not understanding what is referred to. The IS-85 had for its hull armor (ignoring the upper hull side skirt plates):

    a) 120 mm driver's plate, sloped 30 degrees to the veritical
    b) 65 mm upper hull plate, sloped 72 degrees from the vertical
    c) 100 mm lower hull plate, sloped 30 degrees from the vertical.

    The KV-85's armor slope is similar, but the thickness is less (75 mm, 45 mm, and 75 mm, respectively, for 'a', 'b', and 'c').

    Which is which? If the "90 mm top plate" is (b) it's indeed much thicker and only slightly less sloped, and that would be better, but the other points if they retained their armor thickness would be glaring weak points and thus the improvement would not make much sense--increasing the weight but only marginally impacting the survivalbility of the tank.

    The KV-85 made sense as a stopgap. As the article says, given the relatively small numbers of KV-85s produced, not sure that any of these upgunned variants would have made sense unless one was willing to expand the "KV-85" project to include refits of the existing surviving KV-1S and even KV-1 tanks.

    1. The "Improved KV-85" here is an entirely different vehicle altogether. As explained in the article. It was an attempt by LKZ to morph the KV-85 to fit the requirements of the IS-85, but keeping most of KV-85 production. It was never built and its drawings likely have not survived. It seems like the Improved KV-85 would not have a three piece hull front, but only a two parter much like the later improved IS-122.


      a) 90mm driver's plate, sloped 60 degrees to the vertical (note that it says 30 degrees to horizontal, not vertical).
      b) 90mm lower plate, sloped at 30 degrees from the vertical.