Work on Soviet SPGs assigned at the plenum of the Artillery Committee held on April 14-15th reached their logical conclusion by the end of 1942. The light SPG concept turned into the SU-12, designed by factory #38's design bureau and S.A. Ginzburg (the future SU-76). The most promising medium SPG was the U-35, designed at UZTM. By the end of December, the first vehicles of the pilot batch were complete.
The heavy SPG was in a more difficult situation. The project that started as the «212» bunker buster radically changed several times. The ZIK-20 SPG was to go into production, but the process dragged on. Even a model of the casemate was not completed on time, to say nothing of the SPG itself. In the end, another vehicle was developed, the KV-14.
An alternative from Chelyabinsk
After the story with the KV-7, the Chelyabinsk Kirov Factory (ChKZ) did not involve themselves in SPG development. The factory had enough to do with putting the T-34 and KV-1S into production. Nevertheless, regardless of who designed the prospective SPG, it was going to be produced at ChKZ.
The replacement of the KV-1 chassis with the KV-1S postponed any existing bunker buster project. The design bureau of factory #8 bit off more than they could chew with the new SPG, tackling several topics at once. The initiator of work on a new heavy SPG at ChKZ can be gleamed from a factory #100 report from September 15th to October 1st, 1942.
The tank with two coaxial cannons was rejected. The GAU proposed the Kirov factory to install one ML-20 system into this hull. The system has arrived at factory #100. Designers are working on blueprints for the mount, after which they will begin building a wooden model to be presented to the GAU.
The report talks about a Chelyabinsk designed SPG, not the ZIK-20. The factory did not display much enthusiasm about this project. The KV-13 just entered trials in late September, the KV-1S was giving them trouble, and much was still to be done to put the T-34 into production. It's not surprising that work on a heavy SPG proceeded quite slowly at first. Here is how N.F. Shashmurin described it in his memoirs:
Regarding the development of the SU-152, it was not irrelevant what chassis this would be done on. L.S. Troyanov was sent to join our team. He created a draft of a platform with 8 pairs of road wheels that used KV-1S components.
1942 was drawing to a close. It was clear that this suggestion was absurd. The only satisfactory solution would be to retain the KV-1S chassis. Kotin came to my department and drew me a picture: a KV-1S with a 152 mm gun, instead of a turret there was a KV-7-esque casemate. Of course, this was the only correct solution. He told me: «By 3:00 am determine the feasibility of this variant." He left me a sketch of the gun that G.N. Rybin brought from F.F. Petrov. We had the layout finished by morning. N.T. Fedorchuk and M.I. Zeltser did the work. The result had overloaded front wheels and excessive overhang of the gun. A meeting of lead engineers revealed no contrary opinions. The hull designers, led by V.I. Tarotko, and artillerymen, led by F.F. Petrov, had the hardest jobs. The KV-1S chassis was preserved. There wasn't much design to be done, and the SU-152 was ready within a month."
As you can see from this excerpt, the initial heavy SPG design was somewhat different from what was eventually built. The work on this topic was expedited no earlier than the very end of 1942. The blueprint index of the future SU-152 speaks volumes. The vehicle received the index 236. #234 was the KV-13 with a U-11 howitzer (work on this tank began in December of 1942). The next number, 235, was assigned to the KV-8S flamethrower tank. As for #236, later named KV-14 (rarely: SU-14), work on it really started towards the end of December. The reason for this was the same as why this project existed in the first place: issues with the ZIK-20.
A demonstration of bunker busters was held on January 13th, 1943. Factory #9's design bureau, the reorganized factory #8 design bureau, proposed a ZIK-20 that used the KV-1S chassis. This allowed the mass of the new SPG to be reduced, but it was still high: 47-48 tons. GAU did not like F.F. Petrov's idea to alter the ML-20, as this would make production difficult. As a result, factory #9's project was rejected, even though the design bureau already completed working blueprints and a casemate model.
ChKZ's SKB-2 presented two variants of L.S. Troyanov's KV-14 project. Unfortunately, only a text description of the first vehicle survives. It was based on a KV-1S chassis that was lengthened by 450 mm. The number of road wheels remained the same, only the distance between them increased. This variant was unsatisfactory for the commission, as production of a hull that long could run into issues, and increased spacing between road wheels would lead to poor mobility on soft soils.
The second KV-14 variant was chosen as the winner. It retained the chassis and gun unchanged. This vehicle was also a lot lighter. Calculations showed that its mass would be only 45.5 tons. This was more than the KV-1S weighed, but less than factory #9's proposal. The fighting compartment was also better laid out. It's not surprising that this variant was chosen, even though its documentation still needed work.
Stalin signed GKO decree #2692 «On production of a prototype of the 152 mm SPG on the KV-1S chasssis» on January 4th, on the day after the commission's meeting. The characteristics of the vehicle were copied from the second KV-14 variant. The decree provided ChKZ and factory #9 with a difficult task. The gun mount was to be delivered by January 23rd, and the prototype had to be ready for trials on the 31st.
On January 5th, Zaltsmann issued order #6ss «On the production of a 152 mm SPG on the KV-1S chassis». According to the order, chief designer Zh.Ya. Kotin would deliver the blueprints by the 10th. Factory #200 would deliver a complete hull by January 18th. Assembly of the KV-14 would be complete by January 25th. Factory trials would be complete by January 29th, and the vehicle would be sent for proving grounds trials by February 1st. Tactical-technical requirements were finalized on January 6th, and were generally the same as those stated in the GKO decree.
Work started at SKB-2 immediately after the order was received. According to GBTU reports, the first blueprints were delivered to production on January 8th, and the last on January 10th. Parts were assigned to each plant on the next day. Work on a model proceeded in parallel. The KV-14 armour model was built by the 14th, and the full model was built and approved on the 17th. Factory #200 completed the casemate plates by the 19th, and installation on a KV-1S hull began immediately. A complete hull was delivered on the next morning. Assembly work began the same day: the engine and gearbox were centered, torsion bars and suspension arms were installed.
Work on producing an SPG variant of the ML-20 gun was underway at factory #172 in parallel. On January 11th, 1943, this variant was given the name ML-20S (ML-20-S and ML-20s were also used). The gun was held on a frame, protected with an armoured cover and massive gun mantlet. The mantlet had an opening in it to allow service of the recoil mechanisms, covered with a cover. A hydraulic pump was used to fill the mechanism with fluid. A special slot for the pump was added to the front of the hull, where it was fitted during service. Since removing the muzzle brake would have introduced too many changes, it was left as is. As per the customer's requirements, the variable recoil length mechanism was removed, and the tail rod was set to short recoil operation. Half-round elevation and traverse mechanisms with worm gears were added. A loading tray was added to the cradle, which doubled as a guard rail for the loader.
The biggest change in the ML-20S compared to the towed gun was the installation of a T-9 (TOD-9) sight, initially designed for the KV-2 tank. The T-9 was a modernized KT-1 (casemate-telescopic) sight for the DOT-4 fortress gun. The prism in its design gave it a characteristic «knee bend». The PG-1 sight with a Hertz panorama was left for indirect fire. The T-9 sight was considered a temporary measure, and later the T-10 sight would be used, which had markings for ML-20 ballistics. In practice, initial production KV-14s were built with T-9 sights.
The design of the vehicle diverged from initial requirements slightly. The KV-14 was supposed to have a crew of six, but the dimensions of the fighting compartment left no room for a radio operator. This issue was resolved by assigning the gun commander to the the radio operator. The dimensions of the fighting compartment also did not allow the use of KV-1S fuel tanks. Instead, new fuel tanks were placed along the right of the casemate, 480 L in total. This placement of fuel tanks made them more vulnerable to being hit with an enemy shell, but there was nowhere else to put them.
The initial designs of the Kirov Factory's design bureau were also altered. According to GBTU's requirements, all tanks and SPGs had to be equipped with handrails for infantry riders. Even though the KV-14 had no handrails initially, they were added to the prototype.
Assembly of the prototype KV-14 was complete by the morning of January 23rd. Only the gun was left, and it arrived in the evening. Installation went on all night, and on the next day the final assembly was finished ahead of schedule. As planned, the KV-14 with serial number 3011 set out to factory trials, which were completed by January 29th. Proving grounds trials followed. The KV-14 would have driven for 200 km and fired 296 shots according to initial plans.
However, the actual distance travelled was less: 85 km to the proving grounds and 88 km back. Driving to the proving grounds was done in very harsh conditions. The highway was covered in snow and the temperature was −42 degrees. Water got into the fuel, which led to frequent stalling of the engine. As a result, it took 13 hours to travel 85 km. Gunnery trials had to be shortened. 234 shots were fired instead of 296, 100 of them with increased propellant. No deformation was found after the trials. Rate of fire trials showed an average result of 2.8 RPM. This was less than required, but acceptable for a gun with of this caliber.
The commission made the following conclusions:
- The experimental prototype of the SPG with a 152 mm mod. 1937 gun-howitzer on the chassis of the KV-1S tank designed by the design bureaus of the Kirov factory, factory #172, and factory #9, and produced by factory #172 and the Kirov factory, satisfies the requirements for this kind of SPG and has passed proving grounds trials.
- This SPG is recommended for service with the Red Army artillery branch and immediate production after the introduction of changes listed in section A of part VI of this report.
- Task the Kirov Factory, factory #172, and factory #9 with the development of an SPG described in section B of part VI, delivering it for review by the Artillery Committee by March 15th of this year.
The Red Army finally had a heavy SPG that was approved for mass production. It was radically different from what the military wanted initially, but it matched the realities of war. The development of this vehicle did not go unseen: Zh.Ya. Kotin, S.N. Makhonin, L.S. Troyanov, and F.F. Petrov were awarded the Stalin Prize «For the development of a new type of artillery armament» in March of 1943.
Evolution without drama
As mentioned above, the KV-14 was the last of the SPG triad to enter production. By the time it got on the conveyor belt, Sverdlovsk and Kirov were already building the SU-35 (SU-122) and SU-12 (SU-76). However, both the SU-12 and SU-122 ended up with a large amount of design flaws. The SU-152 was the only one of the three that was put into production nearly unchanged. Of course, it had its issues. The trials commission came up with a list of more than ten items that should be corrected. The rear of the fighting compartment was to be widened, the ML-20 would receive a sliding breech, and the fuel tanks moved out of the fighting compartment. However, these changes were never made.
Stalin signed GKO decree #2883ss «On production of the SU-14 SPG, KV-1S tanks, and hulls in February and March of 1943» on February 14th. According to this decree, 30 KV-14s were due in February and 75 in March. An agreement was made with the factory to set the cost of one SPG at 265,000 rubles. Due to a shortage of components only 15 KV-14s were produced in February instead of 30. This meant that 90 had to be delivered in March: 75 normal ones and 15 to satisfy the shortfall. The situation was critical: only 23 KV-14s were accepted by March 28th, and production was blocked due to a lack of track links. Truly heroic efforts allowed assembly of the rest of the vehicles to be completed in the last 3 days. This manner of production was typical for ChKZ. Considering the fact that the factory built 3 vehicles at once (T-34, KV-1S, KV-14), this was not unexpected.
There were inescapable deficiencies in various components. The gun mount frames often had tolerances that were off, which meant that they had to be trimmed to fit the armour, which introduced delays. Shortages of toolkits, which came along with ML-20S guns from factory #172, were also common.
As mentioned above, initial KV-14 vehicles were equipped with T-9 sights, later replaced with T-10 sights, which were later renamed to ST-10. There were wishes to replace the ST-10 with a sight that didn't have the «knee», but no work was done past experiments.
The first changes to the KV-14 design was made in March of 1943. Changes from the trials reports were implemented. External changes include a rough aiming indicator for the driver, consisting of a sight post welded in the middle of his observation slit. The simplified handrails are also worth a mention. The handrails on initial SU-152s were connected, but in March they became separate, which made production easier. The cap above the gun mantlet also changed. It used to be rounded, but now became more angled. A holder for a pickaxe was added on the rear right side of the casemate.
Even though only one factory built the SU-152, there was a certain variety in its form. Initially the casemate armour was cut very carefully, but there was no time for cosmetics in March. The rear hatch, initially somewhat rounded, became rougher in shape. The sides of the hull were cut roughly, sometimes sticking up past the roof and blocking the observation periscopes. To enable them to see, the plates had to be trimmed. This phenomenon was not present on all SPGs, plus the height of the protrusions could be different, giving the vehicles a certain individuality.
Two types of suspension arms were used: regular and lightened, which were introduced for the KV-1S in December of 1942. A feature of some SPGs was a counterweight on the gun mantlet. It is not a distinguishing feature of some production batch, as it can be encountered on an SPG made in any timeframe.
Issues with components continued into April of 1943. Assembly of the SU-152, which was the new name of the KV-14 as of this month, was delayed due to a lack of guns and wiring for the Luch («Beam») lighting system. As a result, only 31 vehicles were accepted by April 24th. The April quota of 75 vehicles was achieved, but further issues lay in wait. As of May 25th, 1943, only 5 SU-152s were accepted. The fault lay with factory #200, which supplied only 28 hulls by that point. Supply issues with gearboxes and other components were also common. A number of SPGs awaiting correction of defects after participating in training piled up at the factory.
Early June was no better. Based on reports by military representatives, the factory had assembled 36 SPGs by June 10th, but not a single one was accepted. The issue was poor quality of the delivered engines and gearboxes. These components broke down in droves. The situation was corrected only towards the end of the month, when 84 vehicles were accepted instead of 75. The factory also managed to repair 15 SU-152s that were built earlier.
The quotas for SPG production in the third quarter were corrected. Instead of 75 vehicles, 80 SPGs were due in July, and 84 in August and September. In addition, according to an agreement between the Kirov Factory, the NKTP, and the GAU, the cost of one SU-152 decreased to 250,000 rubles. Despite a number of delays, the factory put out 80 SU-152s. Vehicles produced towards the end of the month had some changes. The rear handrail was attached at three points instead of two. Another change was made to the SU-152 and KV-1S at the same time. The exhausts received shorter and more reliable armour covers. The SU-152 remained unchanged from here on until late September of 1943.
August was a calm period for ChKZ. The SPGs were delivered gradually instead of all at once: 28 by the 10th, 36 by the 15th, and the full 84 by September 1st. However, there were some issues that were only revealed after the SPGs were delivered to their end users. The Military Representative at the Kirov Factory, Sharonov, accepted several dozen SU-152s with gun mantlet defects. The opening for the hydraulic fluid tank cap wrench were drilled incorrectly, which made it impossible to refill the recoil mechanism with fluid. This defect was discovered after the vehicles were sent to the Moscow Self Propelled Artillery Center. The omission had to be corrected on the spot with gas cutters.
The final changes to the SU-152 were made at the end of September. A rim was added around the rear pistol port. In addition, it was discovered that fumes gather inside the fighting compartment during combat, which resulted in carbon monoxide poisoning. This issue bubbled up to not just the GABTU, but to the very top. Stalin personally raised the issue during an inspection of new vehicles in the Kremlin on September 8th, 1943. Starting with September 23rd, two fans were added to the roof of the fighting compartment of the SU-152. 84 vehicles were delivered before the end of the month.
The situation with the SU-152 began to change in October. The IS-152 (ISU-152) went through trials during this month. GKO decree #4504 «On the heavy IS-152 SPG armed with the ML-20S gun-howitzer» accepted the vehicle into service on November 8th. ChKZ began preparing for production of the ISU-152. An order to stop production of the SU-152 was given on the same day. The monthly quota was reduced to 42 units. The last SU-152 were finished by November 20th, and the first 5 ISU-152 were complete by the end of the month.
The last SU-152s were delivered after the official end of production. They aren't listed in the factory's reports, but are recorded in the list of delivery of SPGs that were sent to Stalin, Molotov, and Beria every 5 days. According to them, ChKZ delivered 4 SU-152s in December of 1943, and the last two production vehicles were accepted in late January of 1944. This increases the number of SU-152s produced to 670 units.
Even though the first SU-152s were delivered in February of 1943, they arrived on the front lines significantly later. Overloading of ChKZ with three types of vehicles reflected on the quality of their production. Issues with the SU-152 meant that they were only issued in April of 1943.
On February 14th, 1943, at the same time as the KV-14 was accepted into service, Stalin signed GKO decree #2889 «On formation of heavy SPG regiments of the Supreme Command Reserve». According to the document, 16 heavy SPG regiments (TSAP) would be formed: 1 in February, 5 by March 25th, 5 by April 15th, and 5 more by May 25th. The TSAP had 310 men and 12 SU-152s according to TO&E #010/454, accepted in April of 1943. In addition to the SPGs, the regiment also contained a commander's KV-1S and a BA-64 armoured car. The SPGs were split into 6 batteries of 2 vehicles each.
Initially, these units just discovered defects with their new SPGs. For instance, defects were discovered with 7 of the 1536th SAP's SPGs, same with the 1537th. The 1538th SAP had 10 defective vehicles, and the 1539th SAP found defects with all of its SPGs. Because of this, the SPGs took a while to reach the front lines.
However, out of all the three Soviet SPGs developed after the Artillery Commitee plenum, this was the best. The design had no inherent engine group issues like with the SU-76. The fighting compartment was not as cramped as on the SU-122. The design of the SU-152 turned out to be very good. Of the three SPGs, the SU-152 was the only one with a telescopic sight, which came in handy. Fate had a different plan in store for the SU-152 than what was initially envisioned.
The SU-152 made its combat debut in July of 1943, at the Battle of Kursk. The 1541st SAP was helf in reserve in the north of the salient, commanded by Guards Major A.F. Sankovskiy. It's worth remembering that the SU-152 had no AP rounds designed for it, but that did not make the lives of German tankers any easier. From July 8th to 18th, the SAP reported 7 Tigers destroyed, 39 medium tanks, and 11 SPGs. Some publications change 10 of those SPGs into Ferdinands, but authors of such fiction should hold their horses. Nevertheless, these results were very impressive, especially for a debut. In these battles the SU-152 earned the name of Beast Killer. This was an official title, and bestowed only on the SU-152. The soldiers gave the SU-152 a number of their own nicknames, often very inappropriate ones.
The SU-152 became a tank destroyer by necessity. As mentioned above, it had no AP shell. The design process began in April of 1943, and it was officially indexed BR-450 on June 14th, but in practice it only appeared in August. However, the HE shell was a terrifying weapon. The 43 kg projectile carried enough energy to crumble a medium tank upon impact. Even if it did not penetrate the armour of a heavy tank, it still resulted in significant damage. In most cases, a hit from this SPG meant that the enemy was at least partially disabled. The SU-152 was the only Soviet vehicle in 1943 that could combat any enemy tank or SPG.
Of course, the SU-152 had its drawbacks. Complaints were made about the visibility from the fighting compartment. The design of the observation periscopes, which had large dead zones, was often the cause of losses. Complaints were made about the small amount of ammunition. Many units increased the capacity to 25 rounds by stowing 5 additional shells in wooden pallets underneath the gun. A proposal was made to add proper ammunition racks there, but it was never done. The quality of existing racks was also not without issues.
The presence of a large fuel tank in the fighting compartment led to serious consequences for the crew if it was penetrated. Finally, the turning mechanism turned out to be poor. Until the end of production, the SU-152 was equipped with the ML-20S with the old style of turning mechanism that pressed against the driver's shoulder or back in some positions.
Heavy SPG regiments equipped with the SU-152 played an important role in operations from the summer of 1943 to the spring of 1944. Many of the regiments earned Guards status. Most regiments received superior ISU-152 SPGs by the summer of 1944, but SU-152s survived in some units until the start of 1945. One of these units was the 268th Guards SAP. By the start of the Lvov-Sandomierz Offensive, this unit had a mixed composition: both SU-152s and ISU-152s. One of the SU-152s was commanded by Guards Lieutenant S.A. Stychinskiy, who had a wealth of combat experience by then. On July 15th, 1944, his crew faced off against a group of German tanks, destroying 5 of them. Sergei Alexandrovich thanks the hilly terrain for his success. His tank rolled up to the top of a hill, fired a shot, and immediately retreated. Later, Stychinskiy liberated Lvov, fought in Poland, and made it to the victorious end in May of 1945.
Only three SU-152s survive to this day. Two vehicles can be seen in Poland, one more in Patriot Park. The long road to the heavy SPG was not walked for nothing. It didn't end up being a bunker buster, but it turned into a dangerous opponent for any German tank. In this respect, the SU-152 was the best Soviet vehicle in production in 1943.
Translated by Peter Samsonov. Read more interesting tank articles on his blog Tank Archives.
- Central Archives of the Russian Ministry of Defence
- Russian State Archive of Socio-Political History
- Russian State Archive of Economics
- Russian State Archive of Film and Photo Documents
- Author's photo archive
- Interview with S.A. Stychinsky