In June of 1940, the Red Army GABTU began working on modernizing the KV-1 heavy tank. Even though production had not yet fully began, the military already had issues with the tank. This is a fairly ordinary scenario, especially considering the fact that tank development sped up with the start of WWII. According to the GABTU, the KV-1 needed more armour and, more importantly, a more powerful gun. It's hard to argue with the latter, since the Red Army's heavy and medium tanks, KV-1 and T-34, ended up with the same gun.
ZIS-5: three guns under one name
Work initiated by Council of Commissars and VKP(b) Central Committee decree #1288-495ss issued on July 17th, 1940, took two directions. In the first case, the aim was a 76 mm gun with ballistics of the 3-K AA gun. This project resulted in the creation of the T-150 heavy tank. The second variant was an 85 mm gun with ballistics of the 52-K AA gun. It was quickly obvious that a gun of this caliber doesn't fit into the KV-1, which resulted in the transformation of this project into the T-220 tank.
Reports from factory #92 made it clear that the F-27 was not just a paper gun.
Both tank guns were designed at factory #92, headed by V.G. Grabin. The F-34 was chosen as the foundation for the new gun with 3-K ballistics. This choice was no accident. Initially, the KV-1 was accepted into service with the F-32 gun, which had the same penetration as the L-11 gun on tanks produced in 1940. For this reason, the more powerful gun F-34 with ballistics of the 76 mm USV divisional gun (another design by factory #92) was designed using the F-32 base. The order for this gun was given in February of 1938, alongside the launch of the F-32 program. This gun was suitable as a stating point for a new system, although the gun mantlet had to be reworked.
The new gun based on the F-34 was indexed F-27 at the factory. Don't be surprised at this "wandering" of indices, this was normal for factory #92. For example, the 85 mm gun launched at the same time was called F-30 and the 107 mm, later pitched as armament for the KV-3, KV-4 and KV-5 tanks, was called F-42. The 57 mm anti-tank gun, known as the ZIS-2, was initially called F-31, even though it appeared after the F-42.
KV-1 with the ZIS-22 gun, February 1941.
A myth was spread about the F-27 gun, alleging that it was designed in early 1939 and work did not move past the design stage. However, volumes of correspondence in the archives prove that this was far from the truth. Design work on the F-27 and F-30 began simultaneously in June of 1940. Regular reports on the status of tank and anti-tank guns coming from factory #92 indicate that the gun did not stay on paper. Even more, work on the F-27 progressed faster than on the F-30. The working blueprints were sent to production by July 23rd. The F-30 ran into many problems, the biggest of which was that it did not fit into the "small turret", the turret of the KV-1.
As of September 21st, the F-27 was completed, and installed in a T-28 tank. It went through five stages of trials in total, firing 122 shots. The results were satisfactory. The F-30 fired 68 shots by then, which revealed drawbacks of its design.
When the F-27 fired 60 shots on September 26th, problems with the recoil system were discovered. The factory worked on various design defects throughout November. As a result, the work was late, and the F-32 gun was installed in the T-150. In total, the F-27 program cost 260,000 rubles.
Gun mantlet for the ZIS-22, designed at the Kirov factory.
This turn of events did not mean that work on the F-22 ceased. By January 15th, 1941, the first gun was improved and prepared for shipment to the proving grounds. A second prototype was also built and installed in a KV-1. After that, it was discovered that the foot trigger didn't work and that the gun was unbalanced.
By that point, work on the F-30 stalled, since factory #92 designed the 107 mm F-42 gun on their own initiative. This gun looked a lot more promising than the F-30. As for the F-27, this gun vanished from was no longer mentioned after the end of the winter of 1941. The reason was simple: it was renamed. Factory #92 introduced a new system of indices that confused many researchers. The F-27 was now called ZIS-5. This index was picked for a good reason, as the full name of the factory was "State Order of Lenin factory #92 named after I.V. Stalin".
On February 19th, 1941, Deputy People's Commissar of Defense, Marshall Kulik, signed an order on the trials of various guns in KV tanks. Item 4 on the list was as follows: "Install the ZIS-5 gun (F-27 with AA ballistics) into the KV tank (experimental prototype with 90 mm armour). The Kirov factory must deliver the turret for this tank by March 1st, 1941"
The "experimental prototype with 90 mm armour" is the T-221 tank, which was still awaiting assembly. As for the turret, it was eventually sent to factory #92. However, by that point, the issue of armament was up in the air. On March 11th, 1941, intelligence passed on information about heavy tanks that entered production in Germany. As a result, the tank development program was adjusted. The T-150, which would enter production as the KV-3, was no longer needed. Work began, first on the 223 heavy tank, which eventually also received the index KV-3, then the even heavier KV-4 and KV-5.
Nevertheless, work on the ZIS-5 continued, albeit with difficulty. Another tank appeared that could be armed with it: the T-44 (A-44) tank designed at factory #183.
Gun mantlet designed by the factory #92 design bureau. It turned out to be more reliable and easier to produce.
The ZIS-5 fell out of favour by May of 1941. As strange as it sounds, its downfall was the 3-K AA gun. The problem was that production of shells for it ceased in June of 1940, when it was replaced by the 85 mm 52-K. The 3-K and F-34 used different shells, which would have complicated supplies of tank units. Another issue was that the penetration of the 3-K and the 57 mm ZIS-4 (tank version of the ZIS-2) were similar. As a result, work on this version of the ZIS-5 ceased by the end of May.
KV-1 with the ZIS-5 gun, July of 1941.
However, that doesn't mean that work in this direction ended. Factory #92 had a refined system with the same caliber and similar barrel length. It was called F-22, and unlike the 3-K, it fired the same ammunition as the F-34 did.
In parallel with work on the ZIS-5, the installation of the F-34 in the KV-1 turret was surrounded with drama. In Kulik's aforementioned order, this was item #1. The F-34 was delivered to factory #92 on February 2nd, 1941. The reworked gun was indexed ZIS-22. It had a direct connection with the F-27: the F-34 barrel was installed in the existing F-27 mount. The trials program was signed on March 3rd, but the itself arrived only in April. After that, the project stalled. The issue was that the gun mantlet was made of structural, not armour, steel.
Kulik added oil to the fire. In the spring of 1941, the KV-3, KV-4, and KV-5 were now the priority, so the letter from the Kirov factory requesting replacement of the gun mantlet with an equivalent made from armour steel was met with a short reply: "Unnecessary, the ZIS-6 gun is on its way."
The Kirov factory did not agree with the design of the gun mantlet, but took its time with its own version. Meanwhile, the Sword of Damocles in the form of the disappearing stockpile of F-32 guns loomed over Kirov and Chelyabinsk factories. The new gun mantlet design was sent to GABTU only on July 17th, 1941. The design of the mantlet was very peculiar.
The same tank on trials, end of August 1941.
The design bureau of factory #92 had to resolve that problem, and redesigned the gun mantle with Kirov factory's permission. Work clearly began before July 17th, since the factory reported that the work was completely on July 20th. There was, however, a twist: the gun installed on the KV-1 had the ballistics of the F-22 divisional gun. As the accompanying note mentioned, the replacement of the F-34's barrel with a 51.5 caliber long one could boost the muzzle velocity to 780 m/s. This speed was possible with an increased propellant load. In other words, Grabin was trying to pitch a second iteration of the F-27.
One advantage of this gun was that it used the same ammunition as the F-34. Factory #92's gun mantlet turned out to be better, although the overall design was similar to the Kirov one. The gun mantlet was composed of two parts, held together with bolts. Unlike the design from Leningrad, all parts of the Gorkiy design were cast. Special slots were added, which made the design more resistant to hits from the side.
The design of the gun was good, overall. The issue with it was that the F-22 had been out of production for two years.
Even though the gun, which inherited the ZIS-5 index from the F-27, was ready by late July, the KV-1 only arrived for trials on August 29th. Two days before that, factory #92 inspected and marked the system. The reason was that the Gorohovets proving grounds didn't have the necessary equipment.
Designer I.M. Lependin represented factory #92 at the trials, and A.S. Schneidman represented ChTZ. Schneidman used to work on KV armament at the Kirov factory, but was moved to Chelyabinsk by August of 1941. The gun had a barrel length of 50.8 calibers (3866) and a muzzle velocity of 687 m/s. 612 shots were fired in total, and the tank drove for 170 km.
The minimum gun depression of -2 degrees did not impress the military.
Overall, the ZIS-5 passed the trials. However, Grabin's claim that the gun could achieve a muzzle velocity of 780 m/s was questioned by the commission. The issue was that the recoil resistance when using an increased charge was twice as high as calculated. Nevertheless, the robustness of the system was satisfactory.
At the same time, the effort required to elevate the gun increased. This was caused by the fact that the gun was slightly unbalanced. The commission also did not like that the gun depression dropped from 5 to 2 degrees. The designers were tasked with resolving these drawbacks.
Third variant of the ZIS-5, the one that entered production.
According to the records of the Artillery Committee, the gun was accepted into service as the "76 mm tank gun mod. 1941", indexed 52-PT-354V by the GAU. However, the ZIS-5 with F-22 ballistics did not enter service. The issue was with production: the F-22 was not produced since 1939, and it would take time, and more importantly, resources, to resume production at factory #92. F-34 and USV guns were needed like air, and production of F-22 barrels was a costly proposition. ChTZ was also in need of guns right now, instead of in the distant future. Only 13 F-32s were available as of September 1st, 1941. These factors killed off the long 76 mm gun.
Production ZIS-5, from the rear.
A somewhat different gun went into production. The stockpile of F-32 guns at ChTZ dried up, and the issue of putting the F-34 into production was very urgent. The issue was solved simply: the F-22's barrel was replaced with the F-34's. The T-34 and KV-1 had equal firepower once more, but there was no other choice.
The issue of the gun mantlet still remained. Since factory #92's design no longer met the requirements, ChTZ's design bureau pitched in. A 90 mm thick cast mantlet was ready by mid-September. The idea of a two-piece design was rejected. A special access door was added to maintenance of the recoil system. This mantlet was put into production. By the end of September, the issue of the KV-1's armament was solved.
ZIS-5 gun mantlet designed at ChTZ.
The first 17 ZIS-5 guns, initially called F-34 in letters, were shipped in September. The name ZIS-5 finally entered use in November. The name ZIS-5 can refer to three guns with a common ancestor.
As for factory #92's gun mantlet, it was later used to re-arm the Matilda III tank, but work did not move past the prototype stage.
This conclusion to the chapter of installing a more powerful 76 mm gun didn't mean that the whole story was over. Recall that, until the fall of 1941, the KV-1 was considered a temporary measure that would be replaced by the KV-3. In the fall, it was clear that this idea would not work. Interestingly, factory #92's design bureau designed a 107 mm ZIS-6 gun mount with a coaxial 45 mm gun. It's unlikely that this was the factory's idea, it's more likely that someone at the top decided to grow a KV-4 out of the KV-3. When the reality that the KV-3 would not enter production at Chelyabinsk set in, another idea appeared: to make a KV-3 out of the KV-1. Of course, the ZIS-6 was not considered as an option, especially since it never entered production. However, an 85 mm gun was once again seen on the horizon.
The Ural Heavy Machinebuilding Factory (UZTM), the new home of evacuated Izhor factory and factory #8, picked up the development of these systems for a time. Due to the relocation to Sverdlovsk, UZTM was renamed to "Izhor factory" for some time, but Stalin signed GKO decree #1107 on January 4th that returned the old name. Earlier, on December 27th, 1941, GKO decree #1077ss "On building NKV factory #8" was signed. However, production of tanks at Sverdlovsk began deploying even before that.
Production of ZIS-5 guns began at Sverdlovsk, which supplied ChTZ (ChKZ after 1942) with tank guns. New faces joined the design bureau, including L.I. Gorlitskiy. The Gorlitskiy-Petrov duo was in charge of designing new guns for the KV-1.
ZIK-1 tank gun. This gun, designed for the T-34 and KV-1, was the first design of factory #8's design bureau at Sverdlovsk.
The factory's design bureau began working on two guns for installation into slightly modified KV turrets in December of 1941. The first one, a 122 mm howitzer with ballistics of the M-30, was indexed U-11. In the context of this article, the second gun, the U-12, looks much more interesting. This was an 85 mm gun with 52-K ballistics. A new recoil system was designed, which reduced the recoil length from 850 to 450 mm. Like the U-11, the U-12 needed slight modifications of the front of the turret and a new gun mantlet.
According to UZTM's post-war report, the gun was designed and even installed in a tank. However, unlike the KV-9 with the U-11 gun, this tank does not appear in any other documents. There are also inconsistencies with the designers. The UZTM report says that it was designed by V.N. Sidorenko, S.Yu. Rykovskiy, A.D. Zaets, and others. In reality, the work was directed by F.F. Petrov, and L.I. Gorlitskiy was his deputy. However, there are often inconsistencies in UZTM reports, especially for the period of 1941-1942.
ZIK-1 barrel. It was somewhat shorter than on the 52-K or U-12, but the penetration characteristics were not that much lower than of those guns.
Alas, no drawings of the U-12 have been found to date. However, there are some drawings of another gun, which was left out of UZTM's historical reports. This gun is the ZIK-1, a design by the factory #8 design bureau. This bureau, led by F.F. Petrov, was created in February of 1942. As for Gorlitskiy, he headed the UZTM's design bureau. This resulted in two design bureaus in direct competition with each other on two different floors of the same building.
The acronym "ZIK" is decoded as "Zavod imeni Kalinina" (Kalinin factory). Factory #8 received this name at its old location. Work on the ZIK-1 began in March of 1942 and was completed in mid-April. This gun was an attempt to fit an 85 mm barrel into the ZIS-5 gun. In order to achieve this, the barrel had to be shortened to 3400 mm (40 calibers). Even in this condition, the gun was significantly more powerful than the ZIS-5. In addition, the ZIK-1 could fit into a T-34 turret. Nevertheless, the gun remained on paper.
85 mm ZIS-25 tank gun. As you can see, the 85 mm gun can fit into the KV-1 turret, but with some nuances.
A conceptually similar gun was developed at factory #92 starting in October of 1942. The gun project, indexed ZIS-25, was led by engineer D.I. Scheffer. Lependin, who previously headed the ZIS-5 project, also worked on this gun. The main idea of this project was the unification of the 85 mm gun with the ZIS-5, which was already in production. According to the project, only 47 new parts would have to be made.
The barrel was also shorter than on the 52-K, which lowered the muzzle velocity to 757 m/s. According to calculations, this was enough to penetrate 75 mm of armour at 30 degrees from a kilometer away. To compare, the ZIS-5 could penetrate 49 mm in these conditions. The mass of the gun grew by 250 kg in comparison with the ZIS-5. As with the ZIK-1, no changes had to be made to the KV-1's turret or gun mantlet for installation.
The same gun from the rear.
The ZIS-25 project was sent for approval on November 5th, 1942. The reply from GABTU was mixed. Admitting the positive qualities of the gun, its authors fairly pointed out that the rate of fire of the KV-1 with this gun would decrease to unacceptable levels, around 2 RPM. The turret didn't get any larger, but the 985 mm 52-K round was 336 mm longer than the ZIS-5's. The loading process became more difficult.
Technically, GABTU was not opposed to producing the ZIS-25, but they demanded that measures be taken to increase the rate of fire to at least 5 RPM.
The gun was never built in metal. On November 5th, 1942, GKO decree #2477ss created the Central Artillery Design Bureau. Work on the ZIS-25 stopped, but the concept was not abandoned. In the spring of 1943, work on this gun served as the foundation for the S-31 gun. However, it was still plagued with the same issues. TsAKB did not learn from past mistakes and wanted to install it in the rather small KV-1S turret.