Saturday 23 May 2020

Pre-War Potential

As worldwide tank building practice shows, it takes about five years to develop a new tank in peace time from the development of the requirements to the final product. The tank often changes significantly between envisioning and production, as happened with the T-34. The initial requirements for the BT-20 tank composed in mid-October of 1937 described a convertible drive tank weighing 13-14 tons with 20-25 mm of armour and armed with a 45 mm gun or 76 mm L-10 gun. Three years later, the tank that went into production was fully tracked, weighed 25.6 tons, had an L-11 gun and 45 mm thick armour.

The mass grew gradually during development along with the improvement of the tank's characteristics. However, the T-34 was supposed to change significantly by the summer of 1941. This T-34M was the result of changing requirements. The start of the Great Patriotic War got in the way of developing even a prototype, but the T-34M became the starting point for a whole series of tanks and had an effect on the production T-34.

Major modernization

The T-34 tank underwent changes from the very start of production. The turret was widened, instead of a cabin the driver received a hatch. Various additions and improvements were made nearly every month. Someone who is not well versed in these issues might think that the designers delivered an unfinished tank that had to be completed on the go, but that is not the case. Any radically new tank like the T-34 ends up having a settling period such as this.

Work on improving the T-34 was nothing when compared to foreign analogues. The birth of the German Pz.Kpfw.III, the closest analogue and main opponent of the T-34 in 1941-42, was much more painful. Over the first three years of production the Pz.Kpfw.III switched its engine once, the gearbox three times, and the suspension along with the running gear three times. The Pz.Kpfw.III finally settled in the second half of 1940. The Z.W. project had an initial mass of 12 tons, the first production vehicle weighed 15 tons, and the Pz.Kpfw.III Ausf.H already weighed 21.5 tons. 

Torsion bar suspension blueprints for a modernized T-34 tank dated January 17th, 1941.

The example of the Pz.Kpfw.III was not chosen at random. The study of a Pz.Kpfw.III Ausf.G tank purchased in Germany had en effect on the development of the T-34. The armour and armament of the German tank were not interesting to Soviet designers, but the Main Automobile and Armour Directorate of the Red Army (GABTU) and tank design bureaus found it interesting nonetheless. The vehicle had better observation devices, a three-man turret with a commander's cupola, a torsion bar suspension that was better than the T-34's coil spring suspension and a higher top speed. After studying the Pz.Kpfw.III several elements, including the commander's cupola, were developed for Soviet tanks. The requirements for future projects, for instance the T-50, also changed due to this study.

However, the top speed of 70 kph was not all it seemed. The Germans shifted to the production of a Pz.Kpfw.III Ausf.H with a reduced top speed. This was caused by issues with the 10-speed gearbox and rubber road wheel rims, which quickly deteriorated at high speed. The USSR, of course, did not know about these changes, and a letter was sent to the People's Commissar of Medium Machinebuilding I.A. Likhachev with 23 suggested improvements to the T-34 on September 25th, 1940. They included the installation of a commander's cupola, increasing the crew to 5 people, installing a planetary turning mechanism, changing the observation devices, and installing a torsion bar suspension with shock absorbers. Not all improvements were tied to the German tank, but its influence is obvious.

The first variant of modernization with bulges on the sides.

This proposal was actively discussed by the People's Commissariat of Defense and People's Commissariat of Medium Machinebuilding (NKSM). The result was the signing of Committee of Defense decree #428ss "On additions and changes to the tactical-technical requirements of KV, T-34, and T-40 tanks" on November 19th, 1940. The NKSM and NKTM (People's Commissariat of Heavy Machinebuilding) planned a much smaller modernization than the one proposed by the GABTU. The V-2K engine from the KV-1 would be installed, the turret would be widened without expanding the turret ring, and a commander's cupola would be added. The possibility of installing a torsion bar suspension would be considered. This limited transformation can be explained by the desire to obtain perhaps a less perfect, but a more reliable tank, and to do so as soon as possible. The requirements for reliability were also increased. The GABTU considered decree #428ss to be insufficient. It required the widening of not just the turret, but the turret ring (to 1600 mm) and the introduction of a separate commander.

Colonel I.G. Panov, an engineer from the GABTU, arrived at factory #183 and carefully appraised the capabilities of their equipment. According to his report, the factory had sufficient tools to build 1600 mm wide turret rings. He considered the installation of the V-2K engine undesirable. The existing gearbox was designed for a less powerful engine and the lighter A-20 and A-32 tanks. The GABTU also considered the transition to a torsion bar suspension to be very important. Even the BT series had significant pitching, and the coil spring suspension had other drawbacks, including the space taken up inside the hull and cuts that had to be made for the suspension arms in the sides of the tank. Calculations showed that switching to a torsion bar suspension would increase internal space by 20%, lower the mass of the tank by 300-400 kg, improve the fuel capacity from 465 to 750 L, and improve the robustness of the lower side armour. An additional benefit was that factory #183 could already produce torsion bars. The torsion bar suspension was nothing new, the KV-1 and T-40 that were accepted into service on the same day as the T-34 already had it. The T-50 tank was being designed with a torsion bar suspension at that time.

The second variant had the upper side armour split into three sections, two of which were sloped.

A draft Committee of Defense decree titled "On the transition to production of T-34 tanks with a torsion bar suspension" was prepared on January 17th, 1941. It called for two T-34 prototypes with a torsion bar suspension to be built by April 1st, 1941. The turret ring was widened to 1600 mm, the turret crew was increased to 3 people, and a commander's all-around vision cupola was installed. A torsion bar suspension was installed instead of coil springs. Instead of the V-2K, a 600 hp V-5 engine would be installed (a version of this engine supercharged to 700 hp was being tested on the T-150 tank). The top speed of the tank was expected to increase to 65-70 kph. It's impossible to say whether or not this was linked to trials of the Pz.Kpfw.III. 

T-34 modernization variants, seen from above.

The first work on this tank, called T-34-M in correspondence, was ready by mid-February of 1941. Two variants of the hull were being worked on which had little to do with the existing T-34. The front of the hull closer resembled the hull of the KV tank. The driver was moved to the right and the radio operator to the left. The observation devices and DT ball mount remained in the front plate, but the radio operator and driver's hatches were moved to the roof. Observation devices were also added along the sides of the driver's compartment. The rear of the tank changed too and also resembled the KV.

A model of the modernized T-34 tank prepared for March 20th, 1941.

The difference between the two variants was in their approach to widening the turret ring. In the first case, the side was flat and special inserts were welded onto it, similar to how the T-54 was later built. In the second case, the side of the tank was made from two sloped plates that connected in a V shape. Both the fighting compartment and the engine compartment walls were sloped.

This tank is often called A-43 and mistakenly consider it the T-34M that would be put into production.

The turret was the same on both variants. Its shape was similar to the T-50's turret, especially the hatches and the commander's station. Soviet cupolas were conceptually different from those used on German tanks. First of all, the cupola did not have a hatch in it at first. Second, the observation devices were positioned differently. The F-34 gun was still used in this tank, but the mount was different. Instead of a curved front plate with a cutout for the gun, there was now an immobile mantlet made from a complex shaped piece of metal. It was similar ideologically to parts developed in Leningrad, namely the KV-1's gun mount.

General view of the modernized T-34.

Preliminary work on the T-34M was reviewed by the GABTU on February 12th, 1941. Panov was present at the meeting. At that point the running gear was not yet finished, but it was proposed that the tank would shift from using a lantern gear to a star gear.The idea of return rollers was first proposed. As for the drivetrain, a 6-speed gearbox was proposed, giving a top speed of 61 kph. The desire to have a top speed of 65 kph was voiced. There were no complaints about the front, but the rear of the hull had to change. The assessment of the upper hull was mysterious: "the whole variant is the most acceptable of those proposed". The driver and radio operator's hatches were to be made with internal hinges, opening forward. There were no complaints about the turret layout, but Panov demanded that there should be a hatch in the cupola. The design of the pistol port changed, one similar to the Pz.Kpfw.III's pistol port was proposed. As for auxiliary armament, an option for a flamethrower in the hull instead of the machine gun had to be prepared.

The front of the hull was drastically different both from the existing T-34 and the other variants of the T-34M.

GABTU chief Ya.N. Fedorenko signed the tactical-technical requirements for a "T-34 tank with a torsion bar suspension" on March 5th. Interestingly enough, the tank was first called T-60 in the document, and later the designation changed to T-34-T. The running gear should be discussed separately. In addition to the requirement to install shock absorbers on the first and last swing arms, the number of road wheels was increased to 6 per side. They also had internal shock absorption to save rubber. Requirements for a mechanical planetary transmission were developed earlier, on March 3rd. Two variants of the gearbox were being worked on by March 10th, a 5-speed and an 8-speed, both for a top speed of 60 kph. Three types of road wheels, two of which had internal shock absorption, were designed. The diameter of the road wheels was reduced from 830 to 600 mm, the same as on the KV tank (this is why return rollers were needed).

The modernized T-34 was significantly different than the production tank.

A wooden model was finished by March 20th at the design bureau of factory #183. It was inspected on April 10th. In addition to Panov, a number of officers from the GABTU took part in the inspection. It's interesting that the index A-43 is used in the report, the fourth index for the same tank. This index does not appear anywhere else aside from a memo from representative of the Mariupol factory P. Hodos. It seems like this wasn't a real index, but a typo.

The tank had time to change somewhat from when the first drafts were reviewed. The KV-1 type upper front plate was replaced with a design closer to that of an ordinary T-34. The hatches on the roof of the driver's compartment vanished. The old hatch returned for the driver, but this time with two observation devices that could be covered with shutters. Periscopic observation devices for the driver and radio operator were installed in the roof. The observation devices along the sides stayed. The upper sides had a new complex shape, a middle ground between the first and second variants.

The engine compartment roof changed somewhat. Like the KV-1, the exhaust pipes were now on the roof. As for the turret, it changed less noticeably than the hull. Rectangular hatches were replaced with round ones. The commander's cupola changed too and now had a hatch. Pistol ports in the rear of the turret changed to resemble those on the Pz.Kpfw.III and the observation devices in the turret changed too. The turret ring was enlarged to 1700 mm.

View from above. The new engine and 8-speed gearbox can be seen.

The running gear changed the most. As specified in tactical-technical requirements dated March 5th, 1941, the number of road wheels was increased from 5 to 6 per side. The diameter was reduced to 600 mm and they were given internal shock absorption. Return rollers (4 per side) were introduced. The idler and track tension mechanism were changed, the new design was similar to the one used on the KV-1. The tracks changed, they were now only 450 mm wide and had chevrons on their surface. There was also a draft of a 480 mm wide track link driven by a lantern gear. There were plenty of changes to the engine compartment. An 8-speed gearbox was added to work with the 600 hp V_5 engine. The cooling system changed and an inertial starter was added.

Comparison of the silhouettes of the T-34 and T-34M. The hull became lower, but the turret became taller.

The factory presented the modernized T-34 in two variants. The first main variant had a mass of 25.5 tons. The second variant had its hull front and side armour thickened to 60 mm and the turret to 50 mm. The mass increased to 29 tons. According to calculations, the top speed of the first tank was 60.5 kph and the second 55 kph. The commission concluded that the prototypes would follow the second variant with a number of changes that would reduce its weight to 28 tons.

A different T-34M

There are opinions that the A-43 would go into production like this, but they are as erroneous as the index A-43. The commission deemed both variant unfinished and left a large list of desired corrections. The proposed front hull was rejected, and the return to a hull with a connecting beam was requested. The idea of side observation devices for the driver and radio operator was rejected, since they would weaken the armour. There were also complaints about the turret. The commander's cupola would be replaced with a stamped design, the gun mantlet was changed, and the question of a stamped turret would have to be explored.

The commission selected the track with a lantern gear. The idea of a star gear was not fully rejected. The second prototype would be built with this design. They also had to be changed, since the ground pressure would be too high. There were also changes required in other areas. There was no way that the tank represented by the model would be built.

A Pomon-type air filter. Trials showed that it would be used on the modernized T-34.

The improvement of armour was not initiative on the part of factory #183. Improvement of protection was required due to new information becoming available about German tanks. The NKO requested that the armour of KV-1 and KV-2 tanks be improved in mid-March. The T-34 wasn't far behind. Two hulls and turrets were shot up at the shooting range of the Mariupol factory. The trials showed that the only part of the tank immune to the 45 mm gun was the upper front plate. The major modernization became very relevant, as stated in a letter written by Marshal Timoshenko on April 18th, 1941. He required the turret and hull front of the "experimental tank with a torsion bar suspension" to be increased to 60 mm. The mass had to remain at the level of the production T-34, or 27.5 tons.

Installation of new air filters in the T-34M, June 1941.

New components for the T-34M were being designed in parallel with the improved protection. A new type of air filter was one of them. Experimental workshop #540 prepared 8 types of filters with different designs. The Pomon filter was the highest priority, similar to the Vortox type filter that was being designed for KV tanks. The filter showed the best results in trials and was thus selected for the modernized T-34. According to documentation, two air filters were installed and they could be serviced from the fighting compartment.

Cutaway of the T-34M as planned for production, May 1941.

Various decrees changed the look of the T-34M significantly by May of 1941. The hull, turret, engine, transmission, suspension all changed. Instead of a tank that was supposed to be radically different from the existing T-34, this was a hybrid in which the existing vehicle was very noticeable. This transformation was caused by rapidly approaching deadlines while the V-5 and its 8-speed gearbox were still either on paper or still in trials. The more constrained modernized T-34 had a better chance of going into production. This was even more relevant after the signing of NKSM order #193s "On the production of T-34 tanks in 1941" on May 10th, 1941. It required the first prototypes of the modernized tank to be delivered by August 10th, 1941. Production of hulls and turrets was to begin on August 1st. Production was going to be set up before the end of trials. Instead of a wooden model, factory #183 faced full scale production of the tank. The T-34M would be put into production at STZ as of January 1st, 1942.

An upper rear plate of the T-34M's hull with a circular transmission access hatch.

Order #193s became factory #183's driving impulse when it came to the T-34M project. It was no longer just a design project, but blueprints that were gradually being sent to production. Documentation for the production vehicle were being produced as of May, first of all the hull, turret, armament, and engine groups. The hull was more reminiscent of a T-34 hull with features of the draft project as well as new elements. The KV style engine compartment was discarded, but a number of components still changed. One of them was the upper rear plate. Instead of a rectangular transmission access hatch, it was now round. The driver and radio operator remained in the same place as on the production T-34.

Trials of the lower side plate held at the proving grounds of the Mariupol factory, June 1941.

The work performed at the Mariupol factory showed that the T-34M solidly left the realm of theory. The first blueprints arrived in May of 1941 and the factory began to produce components. The factory's proving grounds tested 50 and 60 mm thick plates jointly with representatives from the NII-48 research institute, which dealt with armour. 8 50 mm and 5 60 mm plates were tested. As a result of the trials, the commission concluded that MZ-2 (8S) steel should be used for T-34 production and composed technical requirements for this armour.

The T-34M's commander's cupola.

The hull of the T-34M was closer to that of the T-34, and its turret also underwent changes. The turret ring diameter returned to 1600 mm by May of 1941, but the turret itself looked more like the T-44 heavy tank, which will be discussed later. The commander's seat shifted to the left, which allowed the crew positions to be optimized. The turret roof received a slope and a large ventilation hatch was added to the right of the commander's cupola, also like on the T-44. The number of turret hatches was reduced to two: the loader's hatch and the hatch in the cupola. The cupola had 5 periscopic observation devices located in such a way that they would not let through bullets or shell splinters when penetrated. The large immobile gun mantlet designed in February was preserved, albeit with some changes. The turret would be either welded or cast, and an option for stamping was also explored.

According to plans, 380 out of 500 T-34M tanks produced in 1941 would be equipped with the 57 mm ZIS-4 gun.

The armament of the T-34M deserves a separate telling. The F-34 gun was still a priority, but an alternative appeared in the spring of 1941: the ZIS-4, a tank version of the ZIS-2 57 mm gun. According to order #193s, 380 T-34M tanks out of 500 built in 1941 would have a ZIS-4 gun. 25 would be built in September, 100 in October, 125 in November, 130 in December. The priority is explained by the ZIS-4's higher penetration. Intelligence information suggested that the Germans are building new tanks with thicker armour.

A 34-12-8Sb road wheel with internal shock absorption that was slated for production.

Changes were made to the running gear too. Since the ground pressure was too great, a new type of chevron track was developed. It width increased to 500 mm. Work on the road wheels continued. Road wheel blueprint 34-12-8Sb was ready in May. It looks like this road wheel would go into production. Work on road wheels with external tires also continued. Its blueprint index was 34-12-12Sb and it was approved on June 23rd, 1941.

A road wheel with an external tire. Work on the T-34M ended a week after it was approved.

The start of the Great Patriotic War had a direct negative influence on the T-34M program. According to the first corrections, the production of the modernized tank at factory #183 was delayed until January 1st, 1942. Production at STZ was delayed to July 1st. In reality, work on the T-34M began to die down in late June 1941. Factory #183 has no time for the modernized tank. The front needed existing tanks, the more the better. As a result, the T-34M was only a few months too late to not remain as a paper tank. However, work on the T-34M was not a waste of time. It died to be reborn in the T-34. Factory #183 began to produce T-34 tanks with some elements of the T-34M after its evacuation to Nizhniy Tagil. This includes the round transmission access hatch, gun mount, parts of the turret hatches, and other small parts. The chevron track went into production even earlier. The T-34M was also reborn in 1942, but that was largely a different tank.

A heavy tank in the medium weight class

The story of the T-34M isn't complete without another tank that was being built in parallel and had an impact on its design. This was the T-44 tank, the first one with this index. It is often called A-44, but this index is not used anywhere in the archives and was likely invented alongside the A-43.

The T-44 with a 57 mm ZIS-4 gun, April 1944.

The T-44 first appears in GABTU correspondence dated March of 1941. Unlike the T-34M, this was a heavy tank. It isn't clear who came up with this tank, but it was unlikely to be a grassroots project. It's possible that this was a backup plan in case the KV-3 or the even larger KV-4 and KV-5 hit a dead end. The three KV tanks were ordered in March of 1941 when news about new German tanks arrived. The KV-3, KV-4, and KV-5 weighed 68, 75, and 90 tons respectively. However, even the 63 ton T-220 was already showing issues. The tank suffered from various problems, mostly with the engine and transmission. The first results of trials became known by March, and it's possible that they were the cause for seeking an alternative in Kharkov.

This was the most unusual Soviet tank planned for production in 1941.

This was a much more humble project than the 68-90 ton mastodons. The mass of the tank was 29.5 tons. The armour was 75 mm thick in the front and 60 mm thick on the sides. The main gun was either the 76 mm ZIS-5 (with the ballistics of the 3-K AA gun) or the 57 mm ZIS-4. Auxiliary armament consisted of 3 machine guns. The ammunition capacity was 100 rounds for the main gun and 6000 for the machine guns. The crew was 4-5 men. The tank was planned to have very high mobility for a heavy tank. It would have a 600 hp V-5 engine, which would give it a power to weight ratio of more than 20 hp/ton. The expected top speed was 55-60 kph, not bad for even a medium tank.

The turret of the T-44 tank had a big effect on the design of the T-34M production turret.

The draft project was presented to K.E. Voroshilov, who approved it and gave directions to continue development. In parallel, it was decided that the T-44 would be developed in four variants with different armament, engines, armour, and mass. This is where T-44 projects that are known from the few surviving illustrations and scraps of information come from. Several T-44 variants were prepared in April of 1941. This vehicle, developed under the direction of A.A. Morozov and lead designer I.S. Ber, had several components in common with the T-34M but was arguably the most original Soviet tank of 1941. Since the mass limits were very rigid, an unusual layout had to be used. The fighting compartment was in the rear and the engine was in the middle, shifted to the right. The transmission and drive sprockets were located in the front of the tank.

The driver and radio operator were located in tandem, behind one another. They were housed in a special hump which also held the cooling system. This strange layout meant that the driver and radio operator had to use a hatch in the back of the driver's compartment. The running gear was similar to that of the T-34M, but the drive sprocket and idler were different. A star gear was used rather than a lantern gear.

Overall view of the T-44. It's not impossible that the final configuration would be different.

The armament and turret of the T-44 also look interesting. The creators did not spare machine guns. There were a whopping 6 of them (2 in the hull, 2 coaxial, and 2 in the rear of the turret). The turret was similar to the one that would later go on the production T-34M tank. It could also be either welded, cast, or stamped. One of the biggest changes was the commander's cupola. It had a special blister that would allow the commander to fire two PPSh submachineguns simultaneously. 

Sectional view of a version with the ZIS-2 57 mm gun.

As mentioned above, the tank was planned in three variants. The first would weigh 36 tons and would have the same armour and engine as the proposed project. The armament would consist of a 57 mm ZIS-4 gun with 160 rounds of ammunition. The top speed was estimated at 59 kph. The second variant had a mass of 40 tons, its front armour was thickened to 90 mm, and the turret had the same armour all around. The sides of the hull were 75 mm thick. This tank received a 76 mm ZIS-5 gun with the same 160 rounds. The tank received an 850 hp V-6 engine which gave it a top speed of 65 kph.

Finally, the third variant was a 50 ton tank with a reworked turret and rear hull. The third variant would receive the 107 mm ZIS-6 gun, which meant that the turret and the turret ring would have to increase in size. The thickness of the armour also increased. This tank had a 120 mm thick front hull and turret and 100 mm thick hull sides and rear. The V-6 engine gave it a top speed of 53 kph. This was an analogue of the KV-3, but more mobile, lighter, and with more ammunition (60 rounds for the ZIS-6).

The heaviest version had a larger turret and a 107 mm ZIS-6 gun.

Strangely, the review of the project settled on the first variant with an additional requirement to reduce the mass to 29-29.5 tons. This vehicle is also mentioned in NKSM order #193s given on May 10th, 1941. According to the tactical-technical characteristics presented, the NKSM returned to the initial T-44 variant. Two prototypes were due on October 15th, 1941, to be tested on November 25th. As of May 30th, only one gun was considered for the tank. Production of ammunition for the 3-K AA gun ceased, and the ZIS-5 could be left without ammunition. Instead of the ZIS-5, one of the T-44 tanks would be armed with the F-34. Considering further evolution, the only prospective gun was the ZIS-4.

Work on the T-44 tank did not progress past drafts. Production of armour was discussed at the Mariupol factory and NII-48 and proof plates of the required thickness would be produced. The start of the Great Patriotic War spelled the end of the T-44. Nevertheless, the tank had a chance to be reborn in the summer of 1942, when the creation of the KV-13 was discussed. There was even a draft GKO decree to revive the tank, but it remained just a draft.


  1. This T-44 somewhat gives the impression the designers might have caught a case of the MG bug that long afflicted their US peers (there was a more dramatic outbreak later with the IS-7 too)...

    Though tbf given the assault role envisaged for heavy tanks (and rather larger hulls to work with) piling on that much dakka would have been more conceptually defensible than with something like the M2&3 Lights.

  2. Do you happen to know any existing artwork of the final production T-34M? We added it as a tech option in our HoI4 mod ULTRA, but since according to your work here all artworks we could find would not fit the actual production model.

    1. All existing artwork that I'm aware of is based on the wooden model that would not accurately reflect the final production vehicle.

    2. Thank you very much for the answer! Didn't see it at the time but by now our little project has expanded and some artists have joined us, so we might be able to produce our own artwork for the tank.