Saturday 30 May 2020

T-43, Take One

Factory #183 in Kharkov worked on the T-34M medium tank in the first half of 1941. This tank was supposed to replace the T-34 in the second half of 1941. The start of the Great Patriotic War forced the plans to modernize the T-34 to be corrected. Only a handful of components migrated to the production T-34 from the T-34M. The issue of modernization was revisited in the spring of 1942. Unlike the T-34M, the tank called T-43 was built in metal and its development continued for over a year. This article covers the work performed on the T-43 tank in 1942.

A different T-34M

Factory #183 had bigger priorities than the T-34M after the evacuation to Nizhniy Tagil. Late 1941 and early 1942 was spent setting up production of the T-34. Individual elements from the T-34M migrated to the production tank. The modernization left its trace in the tracks, turret, gun mount, transmission access hatch, and several other elements. The factory still performed experimental work, but there was no major modernization planned anymore. This topic disappeared from the experimental plans of factory #183. Nevertheless, the topic of major modernization cropped up at least once more. Correspondence of the GABTU (Main Automotive and Armoured Vehicle Directorate of the Red Army) dated April 12th, 1942, proposes that factory #174 that was being transferred to Omsk should begin production of the T-34M. The T-34M's advantages included a lower mass, torsion bar suspension, wider turret with a commander's cupola, and larger fuel capacity. This proposal was not supported. Factory #174 did not have the capacity to produce the modernized tank.

A T-34M model shown to Stalin at a meeting on June 5th, 1942.

Meanwhile, the situation with the modernization of the T-34 began to develop in a new direction. The capabilities of factory #183 in Nizhniy Tagil were different than those it had back in Kharkov. This difference had an impact on the look of the T-34 (for instance, the hexagonal turret was put into production in late 1941) and on the future work. This changed the course of work on the T-34's successor. The T-34M that nearly made it into production in late 1941 disappeared. Only the idea of a torsion bar suspension remained.

There was little in common between the T-34M designed in 1941 and the one designed in 1942.

It's hard to say when the second take on the T-34M began. Like the KV-13, the start of the program can be approximately traced to the spring of 1942. The reason for this is that factory #183's reports on experimental work in this period are quite sparse. One thing can be said for sure: the "major modernization" of 1941 had little to do with this work. The main goals were maximum increase of armour protection, preservation of the weight at the level of the production T-34, achievement of reliability and simplicity in production, and retention of as many existing components of the T-34 as possible. These requirements had an effect on the look of the vehicle and its mass. The issue was that various design changes increased the mass of the T-34 tank to 28.8 tons. Considering the requirement to increase the armour, one could forget about a 25-26 ton tank.

The T-34M was crewed by only 3 men.

Factory #183's design bureau prepared a draft project titled "Modernization of the T-34 tank" by May 31st, 1942. The attached memo explained that the project was the result of several iterations of the work. Some say that work at KB-520 led by A.A. Morozov was done on their own initiative (Morozov himself wrote that in the fall of 1942). Further developments make it clear that the T-34M was not a grassroots project. The index T-43 that Morozov allegedly used to refer to the new tank was also not present. This designation appeared much later.

The overall view of the tank.

21 components and assemblies were taken from the T-34. The engine, water radiator (without the collector), Cyclone air filters, main clutch, gearbox, final drives, final drive brakes, and brake bands were unchanged. This throws some researchers off, as factory #183 didn't use Cyclone filters yet (the only factory that had already implemented them was STZ). Morozov also contradicts himself, as he later says that the T-34M used a five-speed gearbox, which was only tested on the T-34 in the summer of 1942.

The memo explained that the 5-speed gearbox improved the mobility of the tank. Other components taken from the T-34 included the electric equipment, seats, instruments, ammunition racks, idlers, road wheels, and track links. The torsion bar suspension was taken from another project, the AT-45 artillery tractor that was being developed to replace the Voroshilovets.

Sectional view of the vehicle. The main goals during development were maximum simplicity and reuse of existing components.

The hull was the first major change compared to the 1941 tank. The hull had the same front slope and connecting beam, but the design was different. The sides of the hull weren't sloped, which made it simpler to produce and reduced the size of the tank, helping to make up for the thicker armour. The hull was 296 mm narrower, 78 mm lower, and 176 mm shorter. The turret ring diameter was reduced to 1420 mm, the same as a regular T-34. Bulges were added to fit the turret. The driver was moved to the right and the hull gunner was removed.

The hull machine gun remained, it was to the right of the driver. The large entrance hatch was also removed and replaced with a small observation port. Now the driver had to enter his compartment through the turret. The design of the engine compartment also changed. Air intake "ears" were introduced, the exhaust pipes were moved to the side. The design of the engine deck and the rear plate change significantly. The fenders and mudguards also changed. Large toolboxes were added along the sides. Very little remained from the T-34M designed in 1941.

The driver was supposed to enter the vehicle through the turret.

The turret was also very different from the one used on the 1941 T-34M. The turret now only fit two people and the turret ring diameter was just 1420 mm. The design changed as well. The protruding gun mount was removed and the turret was once against made in one cast piece. The turret became slightly smaller (100 mm lower) like the hull. The turret and hull were simplified and the number of components was reduced. The production T-34 used 8118 parts but the T-34M used only 5985, of which only 1282 were new.

Little remained from the T-34 and T-34M 1941 by May of 1942.

With all measurements totaled up, the T-34M was shorter than the production T-34 by 145 mm, narrower by 250 mm, and lower by 94 mm. The ammunition capacity was decreased to 64 76 mm rounds and 35 DT disk magazines. The tank was 1.8 tons heavier, reaching the 30 ton mark. The thickness of the front and sides was 75 mm, and the turret armour was 90 mm thick. This tank was as well protected as the KV-1. Due to the high slope, the front hull offered complete protection from the 75 mm Pak 40 gun at all ranged. Rolled 8S steel plates were used to assemble the hull. Despite the increase in mass, KB-520 expected the mobility of the tank to remain similar to a production T-34.

T-34M 1942 turret design.

Some publications state the Stalin and the GABTU met the T-34M with scepticism. Indeed, the diary of People's Commissar of Tank Production V.A. Malyshev has an entry dated June 5th, 1942, the day Stalin was shown models of the T-43 and KV-13. According to it, Stalin said:
"Let's not make new tanks for now. Don't distract the designers from the task of improving and modernizing existing tanks. Of course, all designers want to design a new tank, every designer seeks glory. We must wait. Let's return to the new tanks in a month or two when the designers finished their work."
This didn't mean that the T-34M and KV-13 were abandoned. The GABTU was interested in the tanks. In addition, the author considers that these vehicles were developed on GABTU's orders in the first place. It's as though both tanks were designed to the same requirements. However, the T-34M and KV-13 were interesting rather as potential replacements of the KV-1, as indicated by a report to GABTU chief Lieutenant General Fedorenko dated June 1st, 1942. It criticized the KV-1 for its poor reliability and proposed giving factory #183 and ChKZ orders to develop a replacement. Requirements were attached, calling for a 90 mm thick front hull and a 4 man crew with a dedicated commander in the turret. This was the start of work on the KV-13 with a 3-man turret. As for the T-34M, a document was written several days later calling a variant with a 3-man turret "T-44". Some time later, on July 1st, 1942, a draft GKO decree titled "On production of the experimental T-44 tank and modernization of the T-34 tank" was written.

Installation of the gun in the turret.

Prospective tanks fell off the radar in early July of 1942. I.M. Zaltsmann replaced Malyshev as the People's Commissariat of Tank Production. His task was to radically increase T-34 production. Production of the KV-1 and its replacement, the KV-1S, was reduced as a result. The KV-13 vanished from experimental work lists for several months. The T-34M/T-44 disappeared altogether, but another tank replaced them that was a direct continuation of the same ideas under a different index.

Old friend with a new name

The summer of 1942 was spent radically increasing the rate of production at factory #183. This was directly linked to GKO decree #1879ss "On improvements of T-34 tanks" signed by Stalin on June 5th, 1942. That was the result of the meeting between Stalin and Malyshev where the T-34M model was shown. Improvements to the old tank were planned instead of the introduction of a new one. The improvements included replacing the 4-speed gearbox with a 5-speed one and the addition of a commander's cupola. Item 5, personally crossed out by Stalin, is quite interesting. It mentions the very same T-44 tank proposed in early July.

A T-34 tank with a commander's cupola and 3-man turret tested in the summer-fall of 1942. This tank had an effect on the development of the T-34M which turned into the T-43.

Work on the T-44 ended without having begun and the modernization of the T-34 took a different course. The deadlines set by GKO decree #1879 were quite strict. Two new tanks were due by July 15th and had to be tested by August 10th. In practice, there were three new tanks: one with a 5-speed gearbox (tests began on July 22nd), another one with a 5-speed gearbox (tests began on July 31st) and finally one with a commander's cupola that entered trials on August 9th. Trials of the 5-speed gearbox showed that the mobility of tanks improved and so did the reliability. The new gearbox was put into production as a result of these trials. 

Sectional view of the initial design of the T-43 tank. The commander's cupola is still the old style, like the one used on experimental T-34s in the summer-fall of 1942.

The situation with the commander's cupola was not so clear. A new turret was designed and built to house it. Even though it was based on the existing hexagonal design, it had a number of changes. It was more aerodynamic, the gun mount armour was widened to encompass the whole front of the turret, and the air intake was moved forward. Like on the T-34M and T-50, the commander sat behind the gun and used a cast cupola.

The designers tried to free up as much space as possible for the commander, but his position was still uncomfortable. The turret had no hatch, and its dimensions limited the height of the commander to a medium man's height. The commander had to lower the brass catcher and raise it again to get into his seat. His footholds were unstable and the cupola did not protect the commander from bumps. As a result, the commander would be tired after 1.5-2 hours of driving and the visibility was still unsatisfactory due to the mounting of the prisms. The idea of a cupola itself was deemed good, but the design had to be greatly improved. In practice, the idea of a three man turret with a commander was discarded.

Commander's cupola designed in November of 1942. It was used on the T-43 tank.

Nizhniy Tagil and Chelyabinsk returned to the experimental work rejected in June by September of 1942. Factory #100 in Chelyabinsk built a prototype of the KV-13, and an early one at that (with a two man turret). As for factory #183, it took a different approach. Correspondence from September of 1942 shows that the factory design bureau took into account its experience with the T-34 and the tactical-technical requirements for the T-44. The new tank had a different index: T-43. The biggest difference was a three-man turret, similar to the one tested on the T-34 in the summer of 1942. There was also work to increase the amount of ammunition stored on board and change the idler mechanism. The first T-43 designs were presented by Morozov in September of 1942. A call from Stalin followed in October, who instructed that a prototype must be produced quickly.

The first T-43 prototype, late December 1942.

Despite interest at such high levels of government, work on the T-43 was not as fast as on the KV-13. While Chelyabinsk tested a prototype and altered the design in parallel, the T-43 remained on paper. Tactical technical requirements were prepared by the GABTU only by October 23rd and received by factory #183 by November 1st. These requirements caused an argument between Morozov, the GABTU, and the NKTP. They vastly differed from those that Morozov followed when developing his tank. For instance, an F-34 gun mount with two belt fed coaxial machine guns was planned. An optional 50 mm mortar was required. The ammunition capacity was increased to 100 76 mm gun rounds and 3000 machine gun rounds. The turret ring diameter increased from 1420 to 1600 mm.

The same tank next to a T-34S, an experimental tank with a 5-speed gearbox and 3-man turret.

Morozov rebelled against his new requirements. Meanwhile, the designs at factory #183 were completed. In addition to the T-43, the T-44 (later called T-23) with armour reduced to 45 mm (for a total mass of 26.5 tons) was also planned. An exchange of letters followed where Morozov spoke out against changing the requirements. He estimated that an increased turret ring diameter would raise the mass of the tank by 2 tons. His opinion was considered and on November 8th, 1942, senior engineer of the 6th department of the GABTU BTU senior military technician Rozengart, the supervisor of experimental work at factory #183, composed new requirements. The most contended items disappeared, the amount of required ammunition was reduced to 85 76 mm rounds and 1764 machine gun rounds. The correspondence didn't end there, but Morozov celebrated victory as the tank remained in its initial form.

The chassis changed little, the biggest difference was the turret.

The evolution of the T-34 didn't end yet. The T-34S followed the tank with a commander's cupola. It had not only the three-man turret, but a 5-speed gearbox. The conclusions given after trials in the fall of 1942 had similar results. The cupola and the commander's station needed to be improved. As a result, KB-520 developed an improved cupola by late November of 1942. A 465 mm wide hatch was added, so the commander could enter without climbing over the brass catcher. New observation devices were introduced that made it less likely that the commander would be hit. Thirdly, the shape of the cupola changed. Even though it was designed for the T-34, the first tank to receive it was the T-43.

Additional fuel tanks on the back of the hull.

Due to the various alterations and negotiations assembly of the T-43 only began in December of 1942. Assembly at experimental workshop #540 ended on December 16th. Some changes were introduced into the design in the process. An improved cooling system was designed and built. 30 other changes were made to the blueprints. The chassis was still the same T-43 tank designed in the spring of 1942. Some elements had changed in the meantime, but the general concept was the same. The most noticeable addition was the fuel tanks in the back of the hull. These were the same box tanks as on the T-34, but they were moved to the center. Railings on the side of the hull and the engine deck were also added. As before, reusing T-34 components was a main objective. The T-43 borrowed 24 assemblies from it. This had an effect n its mass. The mass of a regular T-34 reached 30.5 tons by early 1943, and the T-43 was 2.2 tons heavier than that. The ground pressure reached 0.87 kg/cm², which was clearly excessive. The T-44 (T-23) was lighter, but it wasn't built. 

The hull changed a little, including the removal of the hull gun

The turret was changed the most. Its overall concept survived since the times of the T-34M/T-44, but the requirement of adding a third crewman resulted in some changes. The turret was longer due to an expanded bustle. This was done as a result of trials of the T-34 with a 3-man turret. A bulge in the bottom allowed the designers to give the commander's space some more headroom. Initially, the T-43 used the same cupola as the T-43, but it was replaced with a new design in November of 1942. An antenna port was added to the left of the cupola. Unlike the T-34M, the turret had pistol ports in the sides.

The turret was a descendant of the T-34M, but there were many changes.

Trials followed the assembly. By January 1st, 1943, the tank covered 247 km. Factory trials continued until February 25th, by which time the tank drove for 1359 km. 18 runs were made in total on snow covered highways and country roads. The tank then travelled for 1667 km, with an overall distance of 3026 km. Trials showed that the average driving speed was 30.7 kph (in good conditions the T-34 reached 34.5 kph). This was due to the heavier weight of the tank. As for the top speed, the top speed of the T-43 was 49.05 kph, while the top speed of a T-34 with the same 5-speed gearbox was 50 kph. The increase in mass had an effect on the tank's ability to negotiate obstacles. Overall, the difference was not great, just 5% from the T-34. The range of the tank was reduced by 60 km. The changes to the cooling system and air intakes resulted in better cooling during the trials.

Engine compartment.

Studies of the crew conditions were performed separately. A medium sized man dressed in a winter coat could comfortably fit in the commander's position. He could enter either through the commander's cupola hatch or the loader's hatch. It was also noted that the commander is not exhausted during driving. There were no complaints about the gunner or loader's positions. The driver's position was not as lucky. He had to climb in through the turret. It was more comfortable for him to do it from the right side, but the loader couldn't be at his station. There were a number of complaints, such as the inability to adjust the height of the seat and difficulty when working with some levers.

5-speed gearbox.

As it often happens with experimental tanks, the T-43 had a number of defects that had to be resolved. However, the reliability of the prototype was much higher than that of the KV-13 or its successors, the IS-1 and IS-2. The list of defects only contained 10 items, none of which required radical changes. For instance, the peeling of road wheel tires was an issue not just on the T-43, but also on the T-34 and SPGs on its chassis (due to the increase in mass). However, these were just conclusions made by factory #183 staff. The first two items in the conclusions are also interesting.

  1. The tactical-technical characteristic of the T-43 tank make it a high speed heavy tank.
  2. An increase in mass of just 1.7 tons in comparison to the T-43 gives a tank that is better protected in most respects than even the KV-1. The maneuverability and mobility of the T-43 tank remain at nearly the level of the T-34.
Nikolai Fedorovich Shashmurin, one of the creators of the IS-1 (IS-85) and IS-2 (IS-122) tanks blamed Kotin for creating a competitor to the T-34 with the KV-13. This is not the case, not when you considered the "classical" T-34. However, the T-34M developed in 1942 and T-43 are a different story. The fact that Morozov classified his tank as a "high speed heavy tank" showed his goals. The problem was that the requirements for heavy tanks were increased in the fall of 1942, and the same IS-1 (KV-13 #2) increased in mass to 40 tons.

Driver's station.

There were other factors that marred the T-43's position. Trials of the tank lagged behind schedule. The tank travelled for 710 km by February 1st, but at the same time the military representative at factory #183 reported that the factory was not working on improvements or correction of defects. There were more complaints made, 24 in all. Most of them had to do with servicing the vehicle, but there were plenty of design flaws. The driver's vision port didn't provide sufficient vision. Opponents of the T-43 also appeared in the GBTU. One of them was P.K. Voroshilov, K.Ye. Voroshilov's adopted son. Petr Klimentyevich was not against the vehicle overall, but reasonably pointed to its flaws. First of all, even the improved cupola was not perfect. Voroshilov considered the solution to be enlarging the turret ring to 1600 mm.

The observation cupola significantly increased the visibility.

A final list of changes was composed by April 5th, 1943. It included the requirement for a 1600 mm wide turret ring and shifting of the commander's cupola to the left. The hull machine gun and driver's hatch returned. 12 changes were requested in total. Work on the T-43 continued to lag behind. This played a key role in the tank's fate, as the development of armoured vehicles (and countermeasures against it) wasn't sitting still. However, that is a story for another time.

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