On April 15th, 1942, the plenary assembly of the Artillery Committee of the GAU met to discuss further development of self propelled artillery. The decisions worked out in this meeting became key in wartime development of Soviet SPGs. Among others, requirements were confirmed for a heavy SPG that would replace the 212 bunker buster. Work began on this SPG on the KV-7 chassis at UZTM, headed by L.I. Gorlitskiy. By the fall of 1942, the U-18 project was ready, but by that point, a competitor was developed at Sverdlovsk.
Competitor from the Bottom Floor
In February of 1942, artillery production from the Ural Heavy Machinebuilding Factory (UZTM) was transferred to factory #8, which was evacuated in the fall of 1941 from Kaliningrad (modern day Korolev) to Sverdlovsk. The factory director was B.A. Fradkin, same as before the evacuation. F.F. Petrov was appointed chief engineer of the new factory.
New developments of the factory #8 design bureau received the index ZIK (Zavod Imeni Kalinina, Kalinin factory). The first product of the newly minted design bureau was the ZIK-1 85 mm gun for installation in the T-34 and KV-1. Various tank and anti-tank guns bore the ZIK index, as well as howitzers, Supreme Command Reserve artillery, and SPGs. It just so happened that no ZIK project was ever accepted into service, but it would be incorrect to say that Petrov's designers worked for nothing. Factory #8 design bureau's works, including the D-1 howitzer, were later brought to life by the factory #9 design bureau, formed in the fall of 1942.
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Competitor from the Bottom Floor
In February of 1942, artillery production from the Ural Heavy Machinebuilding Factory (UZTM) was transferred to factory #8, which was evacuated in the fall of 1941 from Kaliningrad (modern day Korolev) to Sverdlovsk. The factory director was B.A. Fradkin, same as before the evacuation. F.F. Petrov was appointed chief engineer of the new factory.
New developments of the factory #8 design bureau received the index ZIK (Zavod Imeni Kalinina, Kalinin factory). The first product of the newly minted design bureau was the ZIK-1 85 mm gun for installation in the T-34 and KV-1. Various tank and anti-tank guns bore the ZIK index, as well as howitzers, Supreme Command Reserve artillery, and SPGs. It just so happened that no ZIK project was ever accepted into service, but it would be incorrect to say that Petrov's designers worked for nothing. Factory #8 design bureau's works, including the D-1 howitzer, were later brought to life by the factory #9 design bureau, formed in the fall of 1942.
ZIK-1, the first gun designed by the factory #8 design bureau.
As the summer of 1942 dawned, the design bureaus of the two factories began competing. The fact that Gorlitskiy's UZTM design bureau and Petrov's factory #8 design bureau were located on the 5th and 4th floors respectively of the UZTM factory management building put a spicy twist on the situation. Both UZTM and factory #8 worked on a wide spectrum of self propelled artillery, including light, medium, and heavy SPGs, as well as SPAAGs. UZTM's design bureau worked on orders from the top, while Petrov's collective completed several projects on their own initiative.
The project to install a 152 mm ML-20 into the hull of the KV-7 assault tank made its way to the factory #8 design bureau. According to documents, technical task #5400072 for the "installation of the oscillating part of the 152.4 mm howitzer model 1937 (ML-20) into the KV-7 tank" was issued by the GAU Artillery Committee on June 4th, 1942.
This information doesn't mesh well with a letter from the chief of the Artillery Committee, General-Colonel V.I. Hohlov, addressed to the chairman of the NKV Technical Council, professor E.A. Satel. The letter is also dated June 4th, 1942, and according to the letter, work was already underway. In parallel, the factory #8 design bureau was working on installing the M-30 and U-11 122 mm howitzers into the T-34, ZIK-11 and ZIK-10 respectively. The due dates for these projects were not yet established, and work was moving at its own pace. Due to the importance of this work, the letter proposed establishing a deadline for the draft on June 15th and delivery to Moscow for approval by June 20th. However, these deadlines were not met. In reality, documentation on the ZIK-10 and ZIK-11 was only completed in August.
Sketch of the ZIK-20 from the attached memo.
As for the heavy SPG indexed ZIK-20, work dragged on for even longer. A major cause of this delay was the fact that GAU and GABTU tried to also pawn the development of the equally desired Br-2 armed bunker buster onto the factory #8 design bureau. On June 23rd, 1942, the Deputy People's Commissar of Tank Production, A.A. Goreglyad, wrote a letter to the chief of the GAU, General-Colonel N.D. Yakovlev. The letter proposed tasking the NKV with the production of two prototypes of the 152 mm mod. 1937 gun with a muzzle velocity increased to 750-780 m/s by lengthening the barrel and adding a muzzle brake. Petrov is directly connected to this delay, as his design bureau was responsible for this artillery system.
The initiative, supported from the top, played a cruel trick on the project. As mentioned above, the design bureau of factory #8 was working on various projects in different categories, and ended up overloaded with work. It's not surprising that with this kind of workload, the ZIK-20 was delayed. In addition to all that, 152 mm bunker busters disappeared from the list of GAU and GABTU's experimental work in the summer of 1942, returning only in the middle of August.
In the KV-7's Footsteps
Unlike the U-18 SPG, which was nearly absent from correspondence, the ZIK-20 was actively discussed by GAU and GABTU. Work on the heavy SPG was headed by T.A. Sandler, the chief engineer of factory #8 (head of QC at factory #8 before evacuation). Since the ZIK-20 index was not yet assigned, there was some confusion. Artkom's documents from the second half of 1943 put UZTM and factory #8 projects in one basket, and this position migrated to correspondence and UZTM's reports. As a result, many researchers confused the U-18 for the ZIK-20. Since there were next to no drawings of either vehicle, a big mix-up came about.
ZIK-20 cutaway, September of 1942.
The difference between the ZIK-20 and its competitor from UZTM was the rather arbitrary use of the chassis, which was outlined in the tactical-technical requirements. Only the gun was designed in Sverdlovsk, the chassis was designed by ChKZ. The requirements stated that the KV-7 would serve as the base, and already produced hulls would be used for production. The designers of the U-18 chose this path, but ZIK-20's designers had a different idea.
The explanatory memo attached to the ZIK-20 project, as well as blueprints of the SPG, arrived to the Artillery Committee for review on September 11th, 1942. The explanatory note contains a rather interesting explanation: "The thickness of the sides of the turret is 75 mm. In our understanding, we took the KV-7 as the base, not any specific prototype of it, but we assumed that any KV tank with an immobile turret counts as a KV-7."
The "immobile turret" of the new tank was reminiscent of the KV-7, but no more than that. The new casemate was noticeably longer, completely encompassing the turret ring, and 17 cm taller than that of the KV-7. The fighting compartment and driver's compartment remained joined. Essentially, instead of installing the ML-20 in the KV-7, the factory #8 design bureau proposed an entirely new SPG on the KV-1 platform. The new casemate meant that the hulls already produced by factory #200 were of no use. Also, the ZIK-20's mass was higher than the mass of the KV-2, reaching 53 tons. The explanatory memo mentioned optimistically that it was only 4 tons heavier than the KV-1. It would appear that the factory #8 design bureau was unaware that the KV-1 was being removed from production at the end of August of 1942 in favour of the KV-1S due to its exceptional mass.
The same vehicle from the top. Even though the size of the fighting compartment increased compared to the KV-7, it was still rather cramped for 6 crewmen.
The completely new casemate wasn't the only novelty on the ZIK-20. The gun-howitzer that gave the name to the SPG was presented as minimally changed compared to the ML-20, but still had certain nuances to its design. First of all, the muzzle brake was removed, which was a good decision for an SPG. The vehicle would fight in close quarters with the enemy, and a muzzle brake which raised a cloud of dust when firing was not needed. Its removal caused other changes in the system. The elevation and horizontal traverse mechanisms were changed, and the variable recoil mechanism was removed. The idea of installing an ML-20 gun with minimal changes was also discarded.
Perpendicular cutaway of the ZIK-20. The ammunition rack, positioned on the floor, noticeably reduced the height of the fighting compartment.
On September 15th, the ZIK-20 project was reviewed during a meeting of the NKV Technical Council. The design bureau chief. F.F. Petrov, was presenting the project. His report also included the explanatory memo, blueprints, and calculations. The idea of removing the muzzle brake, which would give away the SPG's position, was approved. Even though Petrov raised the issue of introducing a telescopic sight, his project, unlike the U-18, did not have it. The ML-20 gun was also shifted forward on the ZIK-20 compared to the U-18, which could potentially overload the front road wheels.
The layout of the fighting compartment prompted many questions from the audience. Compared to the KV-7, the angles of the sides were reduced, which reduced the odds of ricochet on impact. Even though the height of the fighting compartment was 1895 mm, the crew had to work in cramped conditions. 395 mm of that height was consumed by the two layer ammunition rack on the floor, which was also uncomfortable to use. In addition, the shells stored along the sides of the fighting compartment increased the chances of detonation if the armour was penetrated. The idea of placing fuel tanks along the sides of the vehicle also caused doubt. A series of questions was asked about the effectiveness of ventilation and protection of the SPG from the rear, where there was not even a pistol port (unlike the U-18, which had a rear DT machinegun).
Gun mantlet design.
Despite all of these drawbacks and the fact that the ZIK-20 had nothing in common with the KV-7, the project was approved. In this case, time was the decisive factor. Even though the U-18 was simpler than its competitor, the project was several days late.
Dreams of Large Guns
In late September of 1942, the assistant to the chief of the 2nd department of the Artkom, Engineer-Major P.F. Solomonov, began working on the support of the ZIK-20 project. This was no easy task, as the ZIK-20 was designed on the KV-1 chassis, and ChKZ began producing KV-1S tanks in September. Solomonov traveled to Chelyabinsk where he had a meeting with Kotin and designers of experimental factory #100. A decision was made at that meeting to reject the idea of using KV-7 hulls completely. Factory #100 and ChKZ agreed to produce a chassis and mount the artillery system and fighting compartment equipment for the Artkom. To improve cohesion, ChKZ sent two designers to factory #8.
This is what the ZIK-20 would have looked like according to the project.
Having arrived in Sverdlovsk, Solomonov reviewed the blueprints and gave the designers necessary directions for changes. On September 25th, tactical-technical requirements were finalized. According to them, the ZIK-20 on the KV-1S chassis would weigh 45.5 tons. Mostly, the characteristics were left the same as on the initial project, but the complaints made during the Technical Council meeting on September 15th.
The factory was tasked with completing the blueprints and building a wooden model of the SPG by October 25th. A brigade of modelers and carpenters was assigned by personal order of factory director B.A. Fradkin. Designer A.G. Usenko was put in charge of the construction. In order to ensure that the project had the required number of designers and draftsmen, factory #8 workers were recalled from agricultural and forestry projects.
It would seem that the 152 mm SPG on the KV chassis was finally getting off the ground after being stalled for half a year. Despite a change of chassis from the KV-1 to the KV-1S, the overall concept did not change, and the project could be finished on time. ChKZ representatives made trips to factory #8 to familiarize themselves with documentation, and work on this subject neared the practical stage. However, the production of the model dragged on, and in late October, an event happened that had a serious effect on the project.
According to decree of the State Committee of Defense (GKO) #2457ss issued on October 30th, 1942, factory #8 was being split into two institutions. One of them, factory #8 would work on AA guns. The other, factory #9, was responsible for howitzers and tank guns. L.R. Gonor was appointed the director of the new factory, with P.I. Maloletov as the factory party organizer. The design bureau of factory #9 was headed by F.F. Petrov.
Wooden model of the ZIK-20, December 1942.
The splitting of the factory into two had a negative impact on building a full sized model of the ZIK-20, but not on other work by the newly formed factory #9. In October, before the split, a large amount of design work on various artillery systems was done under Petrov's supervision. The main idea behind these projects was the use of more powerful barrels on ML-20 and M-30 chassis. At least two of them were built in metal, and one of them was put into production under the index D-1. In the context of this article, the seventh project is the most interesting. Among towed systems, there was a 152 mm Br-2 high power gun and 203 mm U-3 howitzer on the ML-20 mount. Both systems received massive muzzle brakes.
It was logical to transplant the Br-2 into the ZIK-20, since it used the oscillating part of the ML-20 already. According to the design, all that was needed was to chance the cast breech and change the spindle in the recoil brake. according to calculations, equipping the ZIK-20 with the Br-2 increased its mass to 48 tons. However, the design bureau had other ideas about what to put in the ZIK-20:
"Since the 152 mm Br-2 has the same mount, cradle, breech, and recoil brake as the 203 mm howitzer, installing the Br-2 into the cradle of the tank version of the MK-20 opens the possibility of, if necessary, installing the 203 mm B-4 howitzer monobloc barrel and, of course, it will be even easier to install the 203 mm U-3 howitzer."
The biggest hurdle was that the base variant of the ZIK-20 was still the priority. Even with this variant, many issues arose with its production. Due to the reorganization of the factory, design work was delayed. The new factory had no modeling plant, which made things difficult. The wooden full scale model of the ZIK-20 was only finished by December 15th.
The ZIK-20 with a Br-2 gun could have looked like this. The vehicle was designed with the KV-1S as the chassis and a commander's cupola.
GAU chief General-Colonel of Artillery Yakovlev, People's Commissar of Tank Production Zaltsmann, and People's Commissar of Armament Ustinov set the date of review of project documentation on January 3rd, 1943. It occurred on ChKZ territory, and this was not just a conclusion, but a competition with a project provided by the Kirov factory. As a result, the Chelyabinsk vehicle, indexed KV-14, turned out to be better and simpler than the one from Sverdlovsk. Its history deserves a separate article.