Monday 3 April 2023

Heavy Without Alternatives

One can often encounter brainstorms about how individual vehicles or even entire tank building schools ought to have evolved. Most of these brainstorms are done by people that are far removed from the field of history, but sometimes even notorious historians take part in this exercise. Among Soviet tanks, the T-28 is a popular character in alternative history. Modern improvements to this tank know no bounds, but the fact that the T-28 was replaced by the KV-1 and not the T-34 is often ignored, as is the fact that a replacement for the T-28 by the name of T-29 already existed. 

Object 237 accepted into service with the Red Army as the IS-85 (IS-1).

The IS-85 heavy tank was accepted into service with the Red Army on September 4th, 1943. This was the finale of the program aimed at developing a successor to the KV. One can often hear claims that if the KV remained in production and was modernized then it could be made into a heavy tank that was no worse than the IS-85. You may laugh, but these claims were not just made by alternative historians. Attempts to preserve the KV-85 were made at the highest levels, even in 1944. Nevertheless, the KV had to make room on the assembly line for its successor. Read on to find out why this happened and why there was no alternative to the IS tank.

A platform with limited potential

Before talking about the IS, let us briefly cover its predecessor's history. The KV-1 was a true revolution in its time and one of the greatest successes of Soviet tank building. Without disparaging the T-34's creators, one must admit that it was nevertheless a further development of the BT series. As for the KV, this was an entirely original vehicle. While the concept didn't come from nothing, the difference between it and its predecessors (the T-28 and T-29) is much greater than between the T-34 and BT-7, and that's without considering the other intermediate designs. The KV also had fully fledged anti-shell armour. The SMK-1 had only 60 mm thick armour, but the KV's armour grew to 75 mm.

KV U-0. On paper it weighed 40 tons, in reality it was 42.

The powerful armour was combined with relatively low weight. The tactical-technical requirements limited its mass to 40 tons. The real KV U-0 weighed 42 tons, but this was tolerable. The Kirov factory initially concealed the increasing weight, continuing to report that it weighed 40 tons. Some elements of the KV never made it onto the tank. Even at the model stage, the review commission commented that the optimal variant would include a planetary gearbox (inspired by the LT vz.35) with a reducer. Permission to use a mechanical gearbox as a backup was given, which the Kirov factory took advantage of. Only a 5-speed mechanical gearbox was built in metal, the planetary one was abandoned. This gearbox gave issues during the first trials.

The KV continued to grow in weight. Note the mass of the KV-2 U-4. The KV-2 with a lowered turret appeared for a good reason.

The gearbox was improved, but all of its issues were never ironed out. This did not stop the acceptance of the tank into service. The "KV with a large turret" appeared after. This tank was later named KV-2 and its predecessor was renamed KV-1. The vehicles developed in parallel, but the KV-1 is the one we're interested in today. KV-1 U-7 went into trials in May of 1940. This tank weighed 44 tons. It only drove for 113 km between May 11th and May 15th. Such a small range is explained by numerous defects. The U-7's gearbox worked well, but there were other issues. This is not a surprising turn of events. New tanks, especially heavy ones, suffer from teething troubles. There is a reason why N.F. Shashmurin, the designer of the KV-1's planetary gearbox, referred to heavy tanks as "tanks with maximum parameters". It's hard to argue with that assessment.

The KV-1's weight characteristics as of January 1941 caused a scandal in the GABTU. The tank grew by another two tons as a result of changes made in the second half of 1940.

The mass of the tank continued to grow due to various changes. A scandal took place in early 1941 as a result. On January 24th, Kirov factory director I.M. Zaltsman sent a report to the GABTU on the characteristics of the KV-1 and KV-2. The KV-1 weighed 46 tons by then. The GABTU issued a furious reply, but the scandal was suppressed. The manual did not mention the weight at all. This weight came as a result of a few changes. For instance, the shape of the turret was simplified. Installation of the F-32 gun began in December of 1940, which had a thicker and heavier gun mantlet. A bow machine gun was also introduced, and the DT with its magazines also weighed something. All this added up to two tons.

T-150, the first time the KV-1 reached the 50 ton mark. This did the tank no good.

The first alarm bell rang with the T-150 experimental heavy tank. It is often considered a branch on the KV-1's development tree, but wrongly so. Essentially, this was just a KV-1 with a commander's cupola, 90 mm thick armour, and a 76 mm F-27 gun (the prototype had an F-32). The military was no longer satisfied with the KV-1's firepower, armour, and vision. Since the tank's mass inevitably rose, the tank received a supercharged variant of the V-2. However, under the influence of the same forces as the KV-1, the T-150 weighed 50 tons instead of 48. Trials of the T-150 turned into a headache. The engine continuously overheated and broke. There were also other issues.

An alternative to the T-222 from Fedorenko. Keep this data in mind.

The trials resulted in an improved tank called T-222. It had a new turret with a commander's cupola in the rear and a new design as well as a new 8-speed gearbox. This tank was supposed to go into production as the KV-3 and preparations for its production already started, but there was another KV-3 waiting in the wings. This was a tank that grew out of the T-220. The new KV-3 weighed 68 tons and had a 107 mm ZIS-6 gun. There wasn't enough time to put it into production. This was a blessing in disguise. Fans of alternative history like to draw all sorts of improvements on the KV-1, but this was much more difficult in real life. 120 mm thick armour was required for complete protection from the 88 mm Flak 18 gun. The GABTU calculated that such a tank would weigh 54-55 tons when armed with a ZIS-5 gun (this is what the F-27 was called in the spring of 1941). To take an 85 mm gun, the KV-1 needed a T-220 style turret that would tack on another few tons. The mass of the tank would have surpassed the Tiger. This tank would move, but slowly and painfully. 

KV-1 tanks with applique armour arrived in the summer of 1941. These tanks weighed up to 49 tons. In the meantime, even tanks without extra armour were not getting the best reviews.

The mass of the KV-1 grew without any alternatives. Work on applique armour for the KV-1 and KV-2 tanks began in the spring of 1941. The KV-2 never received this armour since it mass would grow to 55 tons, but the KV-1 did. The full set of armour for the hull and turret weighed another 2940 tons, which increased the weight of the tank to nearly 49 tons. Applique armour didn't last for long. Turrets with 90 mm thick sides were put into production instead and the hulls only kept it on the front. The total thickness of the front armour even surpassed that of the T-150 in places. The new KV-1 weighed 47.5 tons, which was a lot but still tolerable.

Introduction of cast turrets had its downsides.

New problems began in the fall-winter of 1941 when the Kirov factory was being evacuated and the ChTZ became the main producer of KV-1 tanks. When the Kirov factory merged with the ChTZ to create the ChKZ, the tank's mass began to grow again. The simplified running gear and cast components instead of stamped and welded ones added to the tank's weight. The 76 mm ZIS-5 gun also added weight. It had a 90 mm thick gun mantlet. The tank's weight increased by half a ton. The biggest problem was the cast turret. The thickness of its walls reached 100 or even 110 mm. As a result, the tank's mass reached and then surpassed 50 tons.

Attempts to supercharge the KV-1's engine led to nothing good.

The alarm sounded in early 1942. Front line troops were reporting that KV-1 tanks were insufficiently mobile. Attempts to supercharge the engine led to the same results as with the T-150. The real trouble began in the spring of 1942 when gearbox problems became widespread. In part, attention to the issue was drawn by L.Z. Mekhlis. The man was a controversial figure to say the least, but assigning him as Stavka's representative on the Crimean Front had an effect. He didn't just raise awareness of the KV-1 problems, but demanded that NKTP and ChKZ representatives visit the front to see it for themselves.

Above: T-222 gearbox. Below: KV-1S gearbox. One design grew into the other.

The "commissar method" worked. ChKZ woke up from its slumber. Some of its solutions were over a year old, for instance the new 8-speed gearbox was a direct successor to the T-222's gearbox. The idea with a commander's cupola also came from the T-150/T-222. At first, demands from the top to make the tank lighter by thinning out its armour were ignored. The changes were only made on paper, not in production. An event followed that was described by V.A. Malyshev in his journal.

"Lately, comrade Stalin summons me every day. He is deeply involved with improving tanks. Today we had a meeting with comrade Stalin along with comrades Zaltsman, Kotin, and Morozov. Comrade Stalin said that our tanks surpass foreign tanks, including German ones, in technical aspects, but not when it comes to running gear. This is especially true for the KV tank. It's slow and not very mobile. These days, tanks must first of all drive. They drive 150-200 km per day without roads. We made the KV tank too heavy. It's my fault as well, but your fault for not stopping me."

That day, Stalin signed GKO decree #1878 "On improvement of KV tanks". Instead of just a faster KV-1, the Red Army would receive a new tank with a smaller turret, lighter running gear, thinner armour, and 8-speed gearbox. This was already the second tank designated KV-1S. Mass production began in August of 1942. The KV-1S was put into production in a hurry, which led to issues, but the introduction of a lighter KV was the right decision. Reliability and mobility increased. Even though the commander's cupola was far from ideal, its introduction was a big plus, as was moving the commander to the left behind the gunner. The commander started to see a lot better. The KV-1's blindness was solved.

The KV-1S drove well thanks to changes to the transmission and a large decrease in mass. However, ChKZ and the NKTP understood that these are temporary measures.

Two things should be noted about the KV-1S. One was that the mass of 42.5 tons (that slowly creeped to 43.4 tons by January of 1943) was close to that of the KV U-0. This was not a coincidence. The tank returned to the weight category where it was created. The NKTP and GABTU (later GBTU) reacted negatively to attempts to increase the tank's weight. Something similar took place in the 1950s when work to modernize the T-10 was carried out. This situation can be interpreted as an admission of a simple truth. Further development of the KV-1 tank was pointless, especially since the work on its successor was expedited in the fall of 1942.

Stalin vs Voroshilov

The history of the KV-13 tank that later evolved into the IS-1 is long and turbulent. However, there are some elements that deserve to be highlighted. The index KV-13 refers to two tanks that were similar in design but actually quite different. The first KV-13 was the product of a difficult time where everything was being simplified. This was the reason why it had a two man turret, just like the T-34M (1942). Models of these two tanks were presented and rejected at the same time. The T-43 tank that evolved out of the T-34M got a three man turret, but the KV-13 was built as is. One can confidently say that even if the trials of this tank were successful, it would have gone into production only after serious changes. The military was adamant that they wanted a three man turret and such a turret was even drawn. Nevertheless, the tank was build just as the late Tseits envisioned it.

The KV-13 tank looked like this in early June of 1942. The first variant of the tank never got this three man turret.

N.F. Shashmurin took over Tseits' work on the KV-13 after he died. He was not fond of it, and for a good reason. A heavy tank with the size and weight of a medium one was not the best idea. The second variant developed by December of 1942 was noticeably heavier than its predecessor. It also incorporated some ideas from the KV-1S. The two tanks were developed hand in hand from the start, although some changes such as an improved cupola from the KV-1S didn't make it onto the first KV-13. It can be seen on the second KV-13/IS-1. The running gear of the second KV-13 was developed with experience from the KV-1S in mind. The track links came from here as well.

"Sturmovschina" that nearly led to disaster. Fortunately, the GABTU and NKTP included reasonable people who understood that the KV-13/IS-1 could not be produced as is.

The NKTP constantly urged to start production of the KV-13/IS-1. ChKZ and factory #200 began working on a pilot batch of 10 tanks while the prototype was undergoing trials. The unlucky index played its part. No matter how much effort Shashmurin and the rest of ChKZ SKB-2 put into the tank, the limitations of a heavy tank with the weight of a medium remained. The five wheel layout was limiting and the layout of the engine compartment, particularly the cooling system, was poor. The air intakes were splattered with mud as the tank drove, which caused overheating. The order to install an 85 mm gun was received with enthusiasm in Chelyabinsk. There was an excuse to redo the tank and present the Object 237.

Initial Object 237. The protection was the same as on Fedorenko's T-222 presented two years earlier, but the tank weighs only 44 tons and has a more powerful gun.

A fully fledged new generation heavy tank came about as a result of this project. The Object 237 weighed less than a ton more than the KV-1S, but the difference in armour was considerable. The tank's armour was comparable with the T-222 proposed by Fedorenko in the spring of 1941, but it was at least 10 tons lighter. Even without taking the turret into consideration, it's not hard to see how the Object 237 was lighter and easier to produce. Instead of complicated curved rolled plates, only simple plates or cast variable thickness parts were used. To understand the full complexity of the KV-1 and KV-1S tanks, the front curved plate was 75 mm thick at the top and 60 mm thick at the bottom. This was even harder to produce than the T-34's curved front. Now imagine doing the same thing, but with the top part being 120 mm thick instead of 75. The Object 237 was also built at the weight that it was originally designed for.

Object 239. The KV-1S with the turret of the Object 237 weighed 2 tons more than the Object 237.

The KV-85 shows the difference between the two generations of tanks. The KV-1S needed inserts around the turret ring to receive the larger turret. Its mass reached 46 tons, considerably greater than the new tank with the same turret. Interestingly enough, the attempt to accelerate production by putting the turret into service first did not actually speed up anything. The tank was difficult to produce and the process turned into a whole drama. The tank's combat career was also hit and miss. The 85 mm gun was an advantage, but its armour left much to be desired.

The NKTP's reaction to the proposal to "buff" the KV-85. This was a very conservative estimate, as even the variant with the D-5T would have weighed 50 tons.

There are those in the alternative history community that like to "buff" the KV-1S and KV-85. ChKZ director I.M. Zaltsman and chief engineer S.N. Makhonin were the first to make these suggestions. On their initiative, ChKZ SKB-2 developed a modernization of the KV-85. The front and side armour grew to 90 mm and the rear to 75 mm. The mass estimates were pure fiction. The designers expected the mass to reach 45,342 kg, just 60 kg more than the mass of the production KV-85. Remember how much the T-150 weighed? The modernized KV-85 would have weighed a full 50 tons. The NKTP agreed, but their estimate of the mass was still low. In any case, Zaltsman and Makhonin were told to do their jobs instead of fantasizing. 

The KV-122 was not even seriously considered as the mass of the tank likely reached the NKTP's estimates. Kotin decided to play it safe and confiscated all materials on this tank.

There were still attempts to push the KV-1S and KV-85 through. The KV-122 was one of the last attempts. This tank was not taken seriously. The KV's time was done. Any attempt to improve it inevitably resulted in increased weight with all the resulting drawbacks. The Object 237 accepted into service as the IS-85 (IS-1) was the only possible solution. The KV-1S and KV-85 had no advantages even from a production standpoint. 

Read more about the development of the IS tanks in my book, IS-2: Development, Design, and Production of Stalin's War Hammer


  1. Peter, you hinted that you are working on a book on the KV series on your Youtube channel. Is this so?

    1. Not the KV, no. I was throwing around the idea of a KV book and it would definitely pair nicely with the IS book, but my next three (maybe four) titles are already spoken for. That will take me until the end of 2024 at least, so no sense in making any concrete plans this far out.