Monday 22 August 2022

Big Guns for the T-34

There is a large category of fans of alternative history who like to install large guns into small tanks. These people don't exist only on the internet, but also among popular authors of quasi-historical publications. They sometimes even provide some kind of schematics and make grandiose projections. While modern plans have little to do with reality, tank designers many years ago worked towards very similar goals. Every army wanted to put a larger gun into its tanks. This typically happened as a result of increased requirements for tank guns. This process started very early in the USSR. The MS-1, the first Soviet mass produced tank, was built with a 37 mm Hotchkiss gun. This was far from the only weapon proposed for it. The same gun mount could have been a home for a "high power 37 mm gun" or "37 mm Rheinmetall gun". There were many cases where the proposed gun would simply not have fit into the fighting compartment. For instance, this was the case with the AT-1. The 76 mm PS-3 gun failed to enter production and took down the SPG with it. Other 76 mm guns (for instance the L-10) wouldn't fit.

The 85 mm AA gun was seen as a potential anti-tank weapon and tank gun back in the summer of 1940.

The T-34 was not exempt from this desire for large guns. The story of the 57 mm ZIS-4 comes to mind, but the idea to put an even larger gun into a T-34 tank was born long before a Tiger tank was shot up at Kubinka. The decision to build a tank destroyer on the T-34 chassis was made back in June of 1940. It would be armed with the 85 mm 52-K AA gun. There was no AP shell developed for this gun yet, but Marshal Kulik ordered its development in parallel with the development of an SPG. Work simultaneously began on the F-30 tank gun that would be installed in the KV tank. The story of an 85 mm gun in the KV is a separate tale worth telling, but the resulting T-220 tank was far from the only that would have had a gun that shared ballistics with the 52-K.

Draft of an 85 mm ZIK-1 gun in a T-34 tank, April 1942.

Work on the F-30 died down after the 107 mm F-42 (ZIS-6) gun was given higher priority. Work resumed on this type of gun only in late 1941 when the UZTM design bureau led by F.F. Petrov developed the 85 mm U-12 gun. It was designed for the heavy KV-1 tank and shared the cradle and other components with the U-11 122 mm howitzer. A prototype was scheduled to be built, but was never finished for various reasons. Meanwhile, several factories including factory #8 were evacuated to UZTM's grounds. The factory was tasked with producing the 76 mm ZIS-5 gun for KV-1 tanks built in Chelyabinsk. Stalin signed GKO decree #1077ss "On construction of NKV factory #8" on December 27th 1941. Factory #8's design bureau was factored out of UZTM in February of 1942. Petrov was appointed at its helm. Its products carried the index ZIK, and the first project with this code arose not long after: the ZIK-1 85 mm tank gun.

The barrel was shortened to 40 calibers.

Work on the ZIK-1 began in March of 1942 and reached the finish line in mid-April. Petrov followed the tradition of trying to fit in with existing designs and ended up creating a hybrid using parts of the ZIS-5 gun and 52-K barrel. The barrel was shortened to 3400 mm (40 calibers) so the ZIS-5 mount would withstand the recoil of the more powerful round. Installation of this gun into the KV-1 was the highest priority, but installation into the T-34 was also possible. The weapon fit in the tank, at least on paper. Unfortunately, the ZIK-1 quickly died without even causing too much of a stir within the GAU and GABTU. Petrov never returned to the idea of using the ZIS-5 as a starting point for powerful guns, focusing instead on further development of the U-11. This led to the development of the D-5 gun. The decision to develop the U-11 further turned out to be correct, since by accommodating a gun with the ballistics of the 122 mm M-30 howitzer, Petrov created a mount that could take barrels of the 85 mm 52-K AA gun, several 107 mm guns, 122 mm A-19 corps gun, or the 152 mm M-10 howitzer.

This photo illustrates how well an 85 mm round would fit into the T-34 turret. Consider that the DT magazine racks are not installed.

There was also another reason why work on 85 mm tank guns stalled at the drawings stage. It can clearly be seen in the history of the ZIS-25 tank gun developed under the direction of V.G. Grabin in the fall of 1942. Factory #92's designers led by D.I. Sheffer essentially repeated the ZIK-5, combining the ZIS-5 gun mount and 85 mm barrel. This time, the GAU answered. The verdict was that the rate of fire of this gun would not have exceeded 2 RPM. The turret remained the same size, but the length of the round increased by 336 mm compared to the ZIS-5 to 985 mm. This made the loading process very complicated. Grabin agreed with this decision. Later, the ZIS-25 led to another project, the S-31. This time, the turret was changed along with the gun. The GABTU opposed this idea, and so the S-31 was installed in the stock KV-1S turret. The rate of fire was higher than expected (on the order of 5-6 RPM), but it still paled in comparison to the 10-12 RPM achieved by the Object 239. This was also achieved by a well trained crew. In practice, the loading of the S-31 was not trivial. To demonstrate, refer to the photo of an 85 mm round in a T-34 tank. It is possible to load, but the loader will have a hard time guiding in the round without hitting it against the machine gun magazine rack. In this case, the recoil guard is removed. The process would have been even more interesting with it in place.

T-34 tank with an 85 mm S-53 gun, December 1943

The T-34 was not considered a candidate for installation of an 85 mm gun for a long time. In the fall of 1942, the design bureau of factory #92 was partially reorganized into the Central Artillery Design Bureau (TsAKB) located in Kaliningrad (modern day Korolev). A number of designers from other bureaus moved there too, including Ye.V. Sinilshikov, author of the SG-122 SPG. There were also changes in Sverdlovsk. Factory #9 was refactored out of factory #8. F.F. Petrov became the chief designer. Factory #9 and the TsAKB ended up approaching the same goals from different directions. Petrov immediately stated that a larger turret ring will be required for an 85 mm gun. Meanwhile, the TsAKB was fine with the existing turret ring. The idea of installing a 57 mm gun into T-34 tanks was briefly revived around this time, but the Battle of Kursk showed that it would not be enough. There were two ways to go from here: the 76 mm S-54 gun with a 55 caliber barrel or another weapon with the ballistics of the 85 mm 52-K AA gun. Petrov didn't even try to build 57 or 76 mm guns as their future was bleak. On the other hand, the TsAKB built the S-50 "small triplex" with 57, 76, and 85 mm barrels. There were two additional designs: the 76 mm S-54 and 85 mm S-53. Finally, factory #92 developed its own gun, the LB-1, this time without Grabin.

The mantlet of the S-53 was better than the one of the D-5T and LB-1.

Three 85 mm guns entered trials in December of 1943: the S-50 in a T-34 tank with a 1600 mm turret ring and T-43 turret, LB-1 also in a T-34 tank with a 1600 mm turret ring and T-43 turret, and the S-53 in a stock T-34 turret. The experiments were performed at the Gorohovets ANIOP from December 27th to December 30th. The S-50 dropped out almost immediately. The recoil brake broke after 37 shots an the gun was removed from trials. The competition between the S-53 and LB-1 was the most heated. The S-53 fired 743 shots and the LB-1 fired 484 shots. All three guns had issues during trials, but the LB-1 and S-53 had less. The proving grounds staff favoured the S-53. The gun developed under the direction of the aforementioned Sinilshikov was better than the TsAKB's other weapons. Unlike the LB-1, it had no muzzle brake. The recoil mechanisms were more compact and the mantlet was superior to either the LB-1 or the D-5T. The latter was already put into production on the KV-85, IS-85, and early T-34-85 built at factory #112.

Opinions about the crew conditions at the Gorohovets ANIOP.

The main issue with the S-53 aside from reliability was the tank in which it was installed. Even though the S-53 was very compact, the rate of fire was limited to 5-6 RPM with a trained crew. The issues were the same as shown above. The large round and small turret ring made it uncomfortable to load the gun. Trials showed that a 1600 mm turret ring offers many advantages. All three guns failed trials, but the proving grounds suggested that the best solution would be to take the S-53 and put it in an enlarged turret. That was the end result. The S-53 was accepted into service with the Red Army on January 1st 1944 and factories began installing these guns into T-34-85 tanks in March. Grabin did not settle for this outcome. Follow-up trials took place from January 30th to February 2nd 1944. This time, one gun was installed in a T-34 turret and another in a T-34-85 turret. The results were predictable. The stock turret was the subject of many complaints. The gunner's seat was too high up, as a result of which he had to work while standing. The ammunition racks were uncomfortable. This was the end of the idea to put an 85 mm gun into the regular T-34 tank. Factory #92 also had to improve the S-53 gun afterwards, which is why the mass produced gun is called ZIS-S-53.

Trials of the LB-1 (ZIS-100) in the stock T-34-85 turret.

History often repeats itself, and this story is no exception. By the time the S-53 was accepted into service the 85 mm caliber was no longer considered sufficiently powerful. Soviet 85 mm guns couldn't penetrate the upper front plate of Panther tanks even at point blank range. Work on even more powerful systems began. Initially work started on 85 mm guns with increased muzzle velocities, but for various reasons Soviet "hole punches" didn't take off. It turned out that the optimal solution lay elsewhere, in the 100 mm B-34 naval gun. The TsAKB began working on a tank version of this weapon. The gun indexed S-34 was a triplex, compatible with an 85 mm barrel (with increased muzzle velocity), 100 mm barrel, and 122 mm barrel with the ballistics of the A-19 gun. Factory #9 beat them here again with the D-10T. The gun developed under the leadership of V.N. Sidorenko was superior to the S-34. The latter had reliability problems and required changing the layout of the turret. The D-10 was quickly accepted into service with the Red Army. Initially the weapon was supposed to be installed in a medium SPG (the SU-100) and a heavy tank, but trials showed that the D-25T has its advantages. The IS kept its 122 mm gun. 

The results were similar to what happened with 85 mm guns in the T-34.

The idea of installing this gun into the prospective T-44 tank came up in the second half of 1944. This project was called T-44B and later turned into the T-54. The T-44A tank that went into production (the A was later dropped) still had the ZIS-S-53 gun since it needed too many changes to carry the 100 mm gun. Meanwhile, the idea to install a 100 mm gun into the T-34-85 tank arose in early 1945. Two factories promoted the idea: factory #183 supported the D-10T and factory #92 supported its own ZIS-100 (also called LB-1, a second gun with this name). Work went forward with both. Factory #183 understood that it would not be so simple to install a large gun into the T-34-85 and developed a new turret with an 1800 mm wide turret ring on a new hull. Factory #92 must have been populated with the same optimists that worked at TsAKB. Trials of a T-34-85 tank with a 100 mm LB-1 gun in the stock turret took place between April 12th and April 26th 1945. A tank from factory #112 was taken for installation of a 100 mm gun with a muzzle brake. Due to the large rounds the ammunition capacity of the tank dropped to 30 rounds. Factory #183's T-34-100 had the same ammunition capacity, but the difference was where it was located. The rear ammunition rack could be used more or less well to achieve a rate of fire of 4.6 RPM. This seems fine, until you learn how hard this was to keep up for the loader. Refer to the photo to see how a round from the D-10T gun fits in a T-34-85 turret. Imagine taking out the shell rotating it, and loading it into the gun. The maximum rate of fire in a stationary tank was just 4.6 RPM.

Both the size and weight of the round have an impact.

The loader's work became even more interesting when using other ammunition racks. The rate of fire dropped to 2.5 RPM, and this was the maximum ROF. The practical ROF was estimated to be about 1.5 RPM. In the end, the Gorohovets ANIOP concluded that the gun could be installed in a T-34-85 tank, but also raised the question of whether or not it should. To compare, the T-54 tank had a peak rate of fire of 8.3 RPM and a practical rate of fire of 6.3 RPM. The fate of the T-34-85 tank with a 100 mm gun was predictable. This is a very educational story of what happens when you try to squeeze a large gun into a fighting compartment that was not meant for it.

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